2011

Archaeological Evidence for Glassworking Guidelines for Best Practice

1 Contents

1 How to use these guidelines ...... 3 6.2.3 Optic blowing ...... 22 1.1 Structure ...... 3 6.2.4 Casting and slumping...... 22 6.2.5 Pressing glass ...... 22 2 What is glass? ...... 3 6.3 Windows and flat glass ...... 22 2.1 Types of glass ...... 3 6.3.1 Broad and cylinder glass ...... 22 6.3.2 Crown glass ...... 22 3 An introduction to making and working glass ...... 4 6.3.3 Cast glass ...... 23 3.1 Raw materials ...... 4 6.3.4 Plate glass ...... 23 3.1.1 Silica ...... 5 6.3.5 Mechanised drawing ...... 23 3.1.2 Fluxes ...... 5 6.4 Decoration ...... 23 3.1.3 Colourants and decolourisers ...... 6 6.4.1 Applied glass decoration ...... 23 3.2 Fritting ...... 6 6.4.2 Impressed decoration ...... 23 3.3 Recycling and cullet ...... 7 6.4.3 Polishing and grinding ...... 23 3.4 Melting ...... 7 6.4.4 Cutting and engraving ...... 23 3.5 Shaping an object ...... 8 6.4.5 Painting, staining and flashing ...... 24 3.6 Annealing ...... 8 7 Materials mistaken for glassworking waste ...... 24 4 The practicalities of investigating a 7.1 Metalworking waste ...... 24 glassworking site ...... 8 7.2 Other high temperature processes ...... 24 4.1 Project identification: 7.3 Plastic ...... 25 anticipating glassworking remains ...... 8 7.4 Geological materials ...... 25 4.1.1 HERs, research agendas and Step reports ...... 8 4.1.2 Historic archives ...... 9 8 Chronological Overview ...... 25 4.1.3 Field walking and geophysical survey ...... 9 8.1 Bronze Age ...... 25 4.2 Planning the project ...... 9 8.2 Iron Age ...... 25 4.3 Fieldwork ...... 9 8.3 Roman ...... 25 4.3.1 Sampling ...... 9 8.3.1 Jewellery, ornaments, counters and tesserae ...... 25 4.3.2 Lifting and short-term storage of glass ...... 10 8.3.2 Vessels ...... 25 4.3.3 Deciding what to keep ...... 11 8.3.3 Windows ...... 26 4.3.4 Dating methods ...... 11 8.4 Early medieval ...... 26 4.4 Post-excavation analysis ...... 11 8.4.1 Jewellery and linen smoothers ...... 26 4.4.1 Typological study ...... 11 8.4.2 Vessels ...... 26 4.4.2 Conservation ...... 11 8.4.3 Windows ...... 26 4.4.3 Scientific analysis ...... 12 8.5 Medieval ...... 26 4.4.4 Treatises and historic archives ...... 13 8.5.1 Vessels ...... 26 4.4.5 Experimental archaeology and 8.5.2 Windows ...... 27 ethnographic evidence ...... 13 8.6 Post-medieval ...... 27 8.6.1 Fine vessels ...... 27 5 What you may find: general indications 8.6.2 Bottles ...... 27 of glassmaking and working ...... 14 8.6.3 Windows ...... 27 5.1 Furnaces ...... 14 8.6.4 Specialised glass ...... 27 5.2 Annealing structures ...... 15 5.3 Fuel waste ...... 16 9 Summary table ...... 20 5.4 Crucibles ...... 17 5.5 Frit ...... 18 10 Where to go for help ...... 30 5.6 Cullet ...... 18 10.1 Further reading ...... 30 5.7 Raw glass ...... 19 10.2 Specialist advice ...... 30 5.8 Waste glass ...... 19 10.3 Useful organisations ...... 30 5.9 Tools ...... 20 Case Studies 6 Interpreting finds: the evidence from 1 Sampling for evidence of glass working ...... 11 different glassworking methods ...... 20 2 Determining the date of glass: windows ...... 13 6.1 Beads, bangles and counters ...... 20 3 Provenancing glass: 1st millennium AD 6.1.1 Hot shaping ...... 20 production and trade ...... 14 6.1.2 Core forming ...... 20 6.2 Vessels and bottles...... 20 11 Glossary ...... 31 6.2.1 Free blowing ...... 20 6.2.2 Mould blowing...... 21 12 References ...... 32

2 1 How to use these guidelines 1.1 Structure 2 What is glass? This document is divided into 12 sections: The aim of these guidelines is to help ‘Who, when he saw the first sand or ashes, archaeologists to recover, identify and Essential information by a casual intenseness of heat, melted into interpret waste from the production and 1 Includes a summary of the most a metalline form, rugged with excrescences, working of glass in Britain, from the Bronze important actions recommended in and clouded with impurities, would have Age to the early 20th century. these guidelines and a description of imagined, that in this shapeless lump lay Surviving glassworking remains how this document is structured. concealed so many conveniences of life, as are likely to be regionally or nationally would in time constitute a great part of the important, as archaeological evidence Background happiness of the world,’ Samuel Johnson in of glassworking is relatively rare. These 2 Describes the main types of glass made 1750 (Johnson 1816). guidelines provide advice on how to in the past and how they diff er from Glass is a versatile and beautiful approach, investigate and interpret one another. material that fi nds a wide range of uses, glassworking sites in order to maximise 3 Provides a brief overview of how glass now as in the past. Products include their archaeological potential. The most was made and shaped, detailing the tableware, storage vessels, window panes, important points are: most common raw materials used to mirrors, jewellery and lenses, and it was make glass and introducing processes also used to decorate other objects. It can 1 Seek expert advice early on in order to such as fritting, melting, annealing and be made transparent or opaque, and in a best anticipate, locate, identify, recover, glass blowing. variety of colours. When hot, glass becomes conserve and interpret glassworking a viscous fl uid, which can be shaped using evidence. Advice and resources many methods, including blowing and 4 Provides advice for investigating a casting (Fig 1). When cool, the amorphous 2 Sample extensively, including from cut potential glassworking site, covering glass hardens into a brittle material, with a features, layers, working fl oors and preparation and planning, fi eldwork and smooth, glossy surface. around and within fi red features; tiny post-excavation analysis. The technology for making glass glass threads discovered in samples may probably originated in the Near East in provide the only conclusive evidence of Evidence of glassworking the second half of the 3rd millennium BC glassworking. 5 Describes and illustrates the most and became widespread from the mid-2nd common types of glassworking evidence millennium BC. A little glass is known in 3 Retain all evidence from small sites, encountered on archaeological sites, Britain in Bronze Age contexts, but it is rare which will include most early ones. At such as furnaces, crucibles, waste glass before the late Iron Age. larger sites, for example post-medieval and raw glass. A glass is formed when a melt cools and historic glassworks, there may be 6 Lists common methods of shaping too quickly to crystallise and so keeps a in excess of 50kg of glass and 500kg glass and the types of diagnostic waste disordered, non-crystalline structure. of crucibles. If retaining everything is produced. This enables evidence of Glass can be made from many diff erent impractical, record approximately how particular processes to be recognised, for materials and with widely varying chemical much of each type of material is present example glass blowing. compositions (see sections 2.1 and 3.1). overall and ensure that a representative 7 Describes materials that might Glassy materials are found in nature, proportion of each is kept from the full be misinterpreted as evidence of obsidian volcanic glass being a well known range of phases, contexts and material glassworking. example, and are also common waste types. products from high temperature events, Reference sections such as fi res or metallurgical processes. 4 Consider ways of dating the glassworking 8 Provides a chronological overview, However, the main focus of these guidelines activity, such as archaeomagnetic or highlighting the diff erent types of glass is glass that has been made intentionally. radiocarbon dating. used, and products made, by period. Some other manufactured materials, such 9 Comprises a table summarising raw as Egyptian blue and faience, which are part 5 Plan for specialist study of assemblages materials, processes, products and the glassy and part crystalline, are described and scientifi c analysis of glassworking state of current knowledge by period. in the glossary, but are otherwise not waste. 10 Suggests where to obtain additional discussed. help. The approximate date ranges for the time 11 Contains a glossary. 2.1 Types of glass periods used in the text are as follows: 12 Is the reference list. In the past glass was made from silica, which was combined with a range of Case studies other raw materials to make glass with Bronze Age 2500 BC–700 BC Three case studies demonstrating the widely varying properties (see section 3.1). Iron Age 700 BC–AD 43 potential of sampling strategies and Archaeological glass can be transparent scientifi c analysis occur at intervals through or opaque, strongly coloured, pale blue- Roman AD 43–410 the text. These are: green or colourless. Fragments of vessels or Early medieval AD 410–1066 windows can be extremely thin, while other 1 Sampling for evidence of glassworking types of vessel, or working waste, may be Medieval AD 1066–1485 2 Determining the date of glass: windows thick and chunky. Post-medieval AD 1485–present 3 Provenancing glass: 1st millennium AD The survival of glass diff ers greatly production and trade depending on its type and burial conditions

3 (see section 4.2). If it has survived well, the 2 Potassium-rich ‘potash’ glass – shaping the glass into an object (secondary glass retains a smooth surface and is hard sometimes known as ‘forest glass’ working). In the medieval and post- but brittle; it breaks with a characteristic – is common in the medieval period. medieval periods, these processes took conchoidal fracture. The original colours Sometimes it survives only poorly but, place together at a single site using the are likely to be bright, although there when well preserved, it is transparent same structures. Previously, however, maybe a thin, iridescent altered surface with a greenish colour (Fig 6). the glass was made in one place and then layer. This weathering layer tends to fl ake 3 Lime-rich glass – often called HLLA transported, sometimes vast distances, off (Fig 2). (high-lime low-alkali) glass – is common to other sites, where it was remelted and Some types of glass, from the medieval from the post-medieval period and often shaped into fi nished objects. period especially, are particularly susceptible survives well. It is generally transparent to weathering. When recovered, this glass and greenish in colour (see Fig 2). 3.1 Raw materials can be diffi cult to recognise, as it is fragile 4 Lead glass appears more brilliant than Through the past two millennia a wide and soft, with a crumbly texture. It has an the other types described, owing to a range of materials have been used for making extremely altered appearance – transparent higher refractive index; and it is far glass. Materials varied, depending on the glass may become opaque, and brightly denser. There are some lead-rich early date and location of glass production, and coloured glass may appear dull grey or medieval examples in amber, deep on the product being made (see section 8), brown (Figs 3 and 6). green, red and black. Lead glass vessels but at times the glass industry consumed Other symptoms of unstable glass are were made in Germany and possibly large quantities of resources. Plant ashes the development of a network of fi ne cracks elsewhere in Europe in the medieval were an important raw material from the (crizzling) and a greasy feel owing to period, so rare imports may be found. 10th century, but plants generally produce changes to its surface (Fig 4). Lead glass becomes more common in little ash when burned; for example the In broad terms, there are four main Britain in the post-medieval period, amount of ash produced from oak is less types of glass that have been made or when it is generally colourless (see than 1wt% of the wood burned. Therefore worked in Britain (see section 9). Figs 7, 60 and 61). Some types of to fi ll six pots with plant ash glass in a post-medieval lead glass are susceptible 1 Soda-lime-silica glass (including ‘soda- to problems such as crizzling (see ash’ and ‘natron’ glass) is typical of the Fig 4), and weathered surfaces may Iron Age, the Roman period and much occasionally appear blackened. of the early medieval period, and also more recently from the 19th century. 3 An introduction to making This type of glass often survives burial and working glass well. Soda-lime-silica glass was made in a wide range of colours, but commonest Making a glass object usually involves two Fig 2 (above) Excavated post-medieval bottle glass from are colourless glass, or glass with a pale main stages: making the glass by heating Shinrone glasshouse, Ireland, with a thin, iridescent weathered surface layer; largest fragment 40mm wide. blue-green hue, especially in the Roman and reacting together the raw materials and post-medieval periods (Fig 5). (primary production or founding), and

Fig 3 (above) Roman opaque orange glass vessel from Chichester, West Sussex, weathered to greenish/grey except for the core, c 22mm wide.

Fig 4 (above) Crizzling in a post-medieval lead glass vessel Fig 1 (above) A glassworker reheating a glass object in a replica Roman furnace by Mark Taylor and David Hill. from Wells, Somerset (photo by Colin Brain).

4 3.1.2 Fluxes Silica melts at a temperature above 1700°C, so fl uxes were added to make the silica melt at an achievable temperature. The types of fl uxes used vary over time and depended on the sort of object being made. However, there are two main types of fl ux that result in a glass that is workable at temperatures of c 1000°C or less: alkalis and lead oxide.

Alkali fl uxes

The alkali fl uxes are sodium oxide (Na2O)

and potassium oxide (K2O). They are often found together in ancient glass, so-called ‘mixed-alkali glass’, although generally one or the other will dominate, giving rise to the terms ‘soda glass’ and ‘potash glass’. One source of alkali fl uxes was the mineral trona, formed by evaporation, for example at the lakes of the Wadi Natrun in Egypt (see Case Study 3) (Shortland et al Fig 5 (above) Lumps of waste Roman glass excavated at Basinghall Street, London; that probably fell into the furnace ash pit. 2006). These deposits are commonly The width of the largest piece is 95mm (photo by Andy Chopping/MOLA). known as natron and are a fairly pure source of soda. ‘Natron glass’ was made on a massive scale for more than a millennium, spanning the Roman period. Glass found in Britain from the Iron Age, Roman and much of the early medieval periods is likely to be natron glass. Another source of alkalis was the ashes of certain plants. Plant ashes have complex, variable compositions, depending on the type of plant, the part of the plant burned, the geology where the plant grew, the time of year it was collected and the temperature used for burning. The ashes of plants growing in desert or marine areas, for example the Salicornia species and kelp or seaweed, are often soda-rich. Purifi ed soda-rich plant ashes were used to make the fi nest-quality medieval and post-medieval vessel glass. Large quantities of high-quality ashes, known as

Fig 6 (above) Medieval potassium-rich ‘forest’ glass products barilla, were exported from Spain in the 18th made at English furnaces, excavated at Plantation Place, and 19th centuries for glass production. Ash London. This type of glass is often poorly preserved and from seaweed or kelp was used as a cheaper would originally have been transparent green: top, severely weathered (left) and partially weathered (right) glass Fig 7 (above) A mid-17th-century lead glass vessel with alternative from the 18th century in Britain, fragments, each c 20mm wide; bottom, uroscopy base and patches of black weathering, which is sometimes found on for example for window glass. excavated lead glass (photo by Colin Brain). rim fragments (left) and hanging lamp base, each c 30mm The ashes of fern or bracken species are wide (right) (photo by Rachel Tyson). more potash-rich. Such ashes were probably 3.1.1 Silica used in the production of medieval forest 16th-century glass furnace would have The glass-forming material in ancient glass glass. Plant ashes also contain many other required ash from 50 tonnes or more of was silica (SiO2), which was obtained from components, in particular lime (CaO) and wood as a raw material alone. sand, fl int or quartz pebbles. The silica magnesia (MgO). Although these were often Before use, the raw materials for making source used aff ects the composition and unintentional additions to the glass, they the glass would have been prepared in some properties – colour, melting temperature aff ected its properties, such as durability, way; this is especially the case for colourless and stability – of the glass made. Quartz and acted as fl uxes at temperatures of about glass. Raw materials were sometimes pebbles and fl int are fairly pure silica, but 1300°C or more. Ashes from woody species washed, ground up and sieved to remove sand often contains shell, made of calcium are dominated by lime with less potash. the large lumps. Documents from the 15th carbonate, and varying proportions of other These lime-rich ashes from trees such as century describe glassmakers extracting minerals. The source of silica was particularly beech and oak were probably used to make alkalis, an important glassmaking material, important when making colourless glass, as post-medieval, lime-rich HLLA glass. from plant ash by repeatedly dissolving and even small amounts of iron-rich minerals From the 1830s, synthetic sodium recrystallising the alkalis. would impart a strong colour. sulphate or ‘salt cake’ was used to make

5 translucent colour, including copper oxide (CuO) for turquoise, or green and cobalt oxide (CoO) for dark blue. Deliberate additions of iron gave a range of blue, green or brown colours, depending on whether the conditions were oxidising or reducing, and in large amounts could appear black. Manganese could produce pink or purple colours when present in quantity. Additives that remained as particles in the glass also made it opaque; common examples are lead

antimonate (Pb2Sb2O7) and lead stannate

(PbSnO3) for yellow, calcium antimonate

(Ca2Sb2O7) or tin oxide (SnO2) for white

and cupric oxide (Cu2O) for red. Colourants and opacifi ers were sometimes used in combination with each other; for example, copper oxide blue and lead antimonate yellow together make an opaque green glass. More rarely glass was coloured by nano-particles, making it dichroic, ie it appears one colour in refl ected light and another colour in transmitted light. An example is ruby glass, which was coloured with tiny particles of gold.

3.2 Fritting There is documentary evidence that before melting the glass completely, glassmakers Fig 8 A 16th-century depiction of fritting from Agricola (Hoover and Hoover 1950); the batch was fritted in the upper section often roasted the batch of raw materials of the furnace, then broken up and melted. for up to a day or more, while stirring the sodium carbonate for use in glassmaking. This amounts can give glass a strong colour, mixture. This ‘fritting’ stage may have been very pure alkali fl ux (Muspratt 1860) was which was also infl uenced by the furnace common when plant ashes were used in made from common salt by reaction with atmosphere, whether oxidising or reducing. glass production, ie from the medieval sulphuric acid – known as the Leblanc process. Such glass, coloured by iron oxide impurities period until the early 19th century in Saltpetre (potassium nitrate or nitre, in the raw materials rather than by added Britain (Smedley et al 1998). Fritting helped

KNO3) is another potassium-rich fl ux that colourants, is sometimes called ‘self- to mix and bind the raw materials together, was imported and used to make high-quality coloured’, ‘naturally-coloured’ or ‘blue-green’. eliminated unwanted gases and made lead crystal (Muspratt 1860). The addition In the past, manganese (MnO) or the fi nal melting stage easier and quicker of saltpetre helped to prevent any metallic antimony oxides (Sb2O5) were widely (Paynter and Dungworth forthcoming). lead precipitating and spoiling the glass. added to glass to decolourise it. The resulting frit was broken up and stored Over time, a wide range of methods in a dry place for remelting. Lead oxide to colour glass was discovered. Colorants Some records describe how fritting took Many of the colourants added to ancient that dissolved in the glass produced a place in a cooler part of the same furnace soda-lime-silica glass contain lead, in particular those for opaque red and yellow, and also green if this is made from a mixture of yellow and blue colourants. Lead oxide (PbO) is also a very eff ective fl ux and gives a glass with a low melting temperature that is easy to work. Lead-rich glass was used in the 10th century for beads, trinkets and linen smoothers (see Figs 60 and 61). In the post-medieval period and later, lead oxide was used for making ‘lead glass’ or ‘lead crystal’. Lead-rich glass was prized for its optical properties, as it has a high refractive index and thus looks glossy.

3.1.3 Colorants and decolourisers Much archaeological glass has a blue or green colour caused by iron oxide from impurities in the raw materials; even small Fig 9 A cullet dump from Roman London; the width of the pile is c 0.4m (photo by Andy Chopping/MOLA)

6 that has been collected for recycling is known as ‘cullet’. Cullet dumps often comprise broken vessels and windows, and scraps of glassworking waste (Fig 9). There are descriptions of cullet being collected and traded from as early as the 1st century AD (Shepherd and Wardle 2009), and analyses of Iron Age glass artefacts indicates that this was recycled material from the Roman world (Henderson 1991). Glassmakers added cullet to a batch of raw materials or frit to help these dissolve and speed up the melting process. When freshly made raw glass was in short supply, cullet may have been the main source of glass for working. The glass would have been carefully sorted by type, for example to avoid contaminating colourless glass with coloured cullet.

3.4 Melting Both the making and shaping of glass require considerable heat, which was generated by a furnace. Furnaces were built from refractory materials, such as stone, clay, bricks and tile. Furnace designs changed over time, but there were basically two types: tank furnaces and pot furnaces. Tank furnaces were built with an integral tank to contain the molten glass. There is scarce evidence for these being used in Britain in the Roman period, but there are a number of good examples from the late 19th century (see section 5.1). Most furnaces were pot furnaces, constructed with platforms or shelves to support a number of ceramic containers, known as pots or crucibles, which held the melted glass. Some pot furnaces had a central fi re and ash pit; these were commonly circular in plan but were also sometimes rectangular (Fig 10). Other pot furnaces had an elongated fi re trench and parallel platforms, known as ‘sieges’, on each side for the pots (Fig 11). While the furnace superstructures almost never survive archaeologically, there are a number of depictions of glassworkers and their furnaces, which give us an idea of how they looked in their entirety (Fig 10). These illustrations show glassworkers gathering glass on the end of a long metal

Fig 10 A 16th-century depiction of a glass furnace and workers from Agricola, showing glassblowers and moulds on the fl oor pipe, the gathering or blowing iron, in the foreground (Hoover and Hoover 1950). through holes in the furnace walls. In England, glass furnaces were wood- used for glassmaking, for example on a from fritting is also unlikely to survive; any fuelled until the early 17th century (see shelf within the upper parts of the furnace partially reacted material would dissolve section 5.3). Whereas metalworkers used (Fig 8). Other evidence shows that fritting in the post-burial environment, leaving an charcoal in their furnaces or hearths to took place in a separate structure, known as unremarkable sandy residue. obtain a reducing atmosphere, this was not a ‘calcar’ or oven. Such structures are necessary for glass production or working. diffi cult to identify archaeologically, 3.3 Recycling and cullet Coal-fi red furnaces were introduced from however, as they are unlikely to have reached Recycling glass has been common practice the early 17th century. Gas-fi red furnaces very high temperatures. Diagnostic waste for as long as glass has been in use. Glass were introduced in the mid-19th century.

7 There are also many ways of 4.1 Anticipating glassworking remains decorating cold glass, for example by Before fi eldwork, there is often little to grinding, engraving or cutting (see indicate the presence of early glassworks, section 6.4). but evidence is more likely to be encountered at certain types of site, for 3.6 Annealing example Roman towns and early medieval Glass objects have to be cooled down monastic sites. However, in some periods in a controlled way, or the glass will the industry is concentrated largely shatter. To do this, the hot glass objects in particular regions and it is often possible were ‘annealed’: held at an intermediate to anticipate the presence of glassworking temperature for many hours. This remains. For example, in Britain the temperature is much lower than that Weald and Staff ordshire were focal points needed to melt the glass. However, the for the industry from the 13th to the holding temperature must be hot enough, 17th centuries (Kenyon 1967; Welch 1997). and the subsequent cooling rate slow Similarly, the approximate location of later, enough, to guard against the permanent post-medieval furnaces is often known stresses that would otherwise be created in from maps and records. In addition, the the glass if it were cooled too quickly. following resources and practices can be Sometimes annealing took place in a helpful for assessing the potential of a cooler part of the main glass furnace, in particular site for providing evidence of an annealing compartment. The winged glassworking: extensions on some post-medieval furnaces Fig 11 A rectangular-plan, 17th-century glasshouse at in Britain have also been interpreted as 4.1.1 HERs, research agendas and Shinrone, Ireland, with surviving vaulted sandstone super- possible annealing ovens (Fig 13). Step reports structure. The small holes in the vault are for smoke to escape; there was no chimney. The fi re trench runs through the arched In other cases, a separate structure, Current knowledge can be reviewed in the openings at each end with low sieges on either side. Gases called an annealing oven or ‘lehr’, was used Historic Environment Record (HER), which from the wood fuel have reacted with the stone furnace walls (see section 5.2). The glass was loaded is maintained by local authorities at county, to make a blue glaze-like surface over the inside surfaces. The side walls, which originally would have had gathering holes in into the heated oven, which was sealed district or unitary level, and in many cases them, have not survived (photo by Chris Welch). and allowed to cool. Documentary sources is accessible through the Heritage Gateway imply that ovens remained in use until the website at http://www.heritagegateway.org. 3.5 Shaping an object mid-19th century. Continuous lehrs were uk), and in regional research frameworks Within a temperature range determined used from the 19th century. where these are available (see the website by its composition, glass has the right for the Association of Local Government consistency for shaping by moulding, 4 The practicalities of Archaeological Offi cers (ALGAO) at http:// drawing, cutting, pinching, blowing or investigating a glassworking site www.algao.org.uk/Association/England/ casting. These techniques leave diagnostic Regions/ResFwks.htm). Also an overview marks on the object made, and can also Archaeological work may originate as a of the glass industry is provided in the produce characteristic types of waste response to proposed land development, Monuments Protection Programme Industry (described in more detail in section 6). as a project funded by national agencies Step 1 report and a list of assessed sites An object can be built up in stages using such as English Heritage, or as a part of a with recommendations for their future hot-forming techniques, by applying trails university department or community-led management in the Step 3 report, available of molten glass as decoration and to form archaeology venture (English Heritage for consultation at the National Monuments bases, rims or handles (Fig 12). 2010; Lee 2006). Record (Swindon), the Council for British

Fig 12 Glassworker Mark Taylor, applying a handle to a vessel; Fig 13 Remains of a 17th-century coal-fi red glass furnace at Kimmeridge, Dorset, showing the below-ground fl ue or fi re the red-hot glass has a toffee-like consistency. trench running left to right (photo by David Crossley).

8 Fig 14 Top: an 1897/98 OS map (1:2500) of Lemington glassworks, Newcastle-upon-Tyne, showing the circular footprint of the cones. (This map is based upon Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationery Offi ce. © Crown Copyright). Right: a photograph of the glassworks c 1900 (reproduced by permission of English Heritage.NMR) .

Archaeology (York), Leicester University • Contacting specialists in glassworking fuel was used and is there evidence of and the Institute for Industrial Archaeology evidence and conservation, who can woodland management? Were (Ironbridge). A summary of what to expect advise on the types of evidence likely to materials such as sand, plant ashes at sites of diff erent dates is provided in be encountered (see sections 5 and 6), and clay obtained locally or transported sections 8 and 9 and further reading is sampling, recovery and immediate to the site? suggested in section 10. treatment of glass fi nds (see section 4). 5 Was the glass made at the site; if not, In the WSI the scope of work should be where was the raw glass obtained? 4.1.2 Historic archives outlined and funds allocated for specialist What products were made, where was Documentary records, including accounts, analysis, for example typological study, the intended market and how were maps (Fig 14) and place names can help to scientifi c analysis, conservation and so on. products transported and sold? How locate glassworking sites, in particular for was the glass used? later periods (Crossley 1994; Dungworth • Outlining glassworking research and Paynter 2006). questions, because glassworking evidence 4.3 Fieldwork is rare for many periods, and gaining a It may be necessary to undertake fieldwork 4.1.3 Field walking and geophysical survey better understanding of the glassworking to characterise, understand and record a Field walking may reveal a scatter of activity is likely to be a major aim for any historic resource. At glassworking sites the crucible or furnace fragments and glass site where glassworking has taken place. furnaces and flues are often the initial focus waste in the area of a glassworks. Some research questions that could be of the investigation, extending to ancillary Geophysical survey techniques are likely addressed by the glassworking evidence structures such as annealing furnaces, to be successful in locating some furnaces. for a particular period are highlighted stores, gas ovens and cutting workshops. For example 13th- to 17th-century furnaces in section 9, and examples are also At earlier sites, geophysical survey (see reached high temperatures and are well fi red given below: section 4.1) can guide the positioning of and robustly built. These were also wood-fi red trenches, as can the site topography. For and are often located in rural, or sometimes 1 Particularly for historic glassworking example, mounds can indicate waste tips in urban, areas and may be relatively sites – as this was a period of rapid, (Fig 15). At later sites it can be possible undisturbed. The fi re trench of these furnaces although often secretive, innovation to position trenches making use of is often detectable by geophysical survey in glassworking – is there evidence for contemporary accounts and historic maps (Welch and Linford 2005). the remodelling of structures such as in order to establish the location and furnaces and fl ues, changes to processes preservation of features. 4.2 Planning the project or production of specialised products? Glassworking remains are rare, Having decided that a site requires 2 What evidence is there for ancillary particularly upstanding structures. If archaeological investigation, the historic industrial activity in the surrounding features are well preserved, then this environment planning officer may produce area; for example, were there shelters strengthens the case for preservation in situ; a brief. The developer selects a contractor for the furnace and workers, where guidance on conservation planning and to undertake the archaeological project, were the raw materials stored, where recording is provided by Gould (2008). The and this contractor responds to the brief were the crucibles made and were appointed specialist should be consulted for with a written scheme of investigation activities seasonal? more detailed advice on each case. (WSI) (Association of County 3 What labour force was involved in the Archaeological Officers (ACAO) 1993; glassworking, how were they organised 4.3.1 Sampling Institute for Archaeologists (IFA) 2001 and trained, what conditions did they Detailed and often small-scale examination and 2008). The quantity and quality of work and live in, and is there evidence is particularly important for glassworking information provided by the glassworking of domestic activity? sites. Sometimes the only surviving evidence evidence from a site can be maximised by: 4 How were resources managed? What of glassworking are the small glass threads,

9 Fig 15 The view from the west of Little Birches, Wolseley, Staffordshire, a 14th- to 16th-century glassworking site, showing the waste tips (quartered or sectioned black mounds) and furnaces (orange-fi red areas) (photo by Chris Welch). trails and droplets recovered from soil relatively good condition. Glass is often has a tendency to fl ake off . Conservation deposits (Fig 16). The most efficient way physically and chemically altered, or treatment can prevent the loss of this of recovering this small-scale glassworking weathered, during burial (see section integral weathering crust and safeguard evidence is to take soil samples and process 4.4.2). However, when weathered glass the information that it can contain, in them by flotation and sieving; glassworking is damp it can appear unaff ected, with a particular surface detail and painted waste is found among the residues (see Case translucent and shiny surface, because decoration. Study 1 and English Heritage 2011). It is there is water in between the weathering It may be necessary to lift glass within advisable to sample from layers, including layers and the glass. When the glass dries the surrounding matrix of earth. Glass occupation layers if these survive, and out the weathering layers collapse and should also be well supported during from within cut features, such as pits form a fragile weathering crust, which storage or it is likely to break. and ditches. If fired features are located, samples should be taken from outside (around the perimeter) as well as from inside, because material from inside is more likely to be chemically altered, and so less representative (see section 4.4).

4.3.2 Lifting and short-term storage of glass First Aid for Finds (Watkinson and Neal 2001) provides advice for the recovery and storage of glass on site. The condition of glass is dependent upon the burial environment and the composition of the glass; the latter varies depending on the type of object and when it was made. Water is the main factor causing deterioration of glass and in damp atmospheres potash (forest) glass is more liable to decay than soda-lime-silica glass (Pollard and Heron 1996). It is important for the condition of the glass to be assessed upon excavation, for example by a fi nds specialist or conservator, and to seek advice if necessary (see section Fig 16 Concentrations of glass waste on the working fl oor below the gathering hole of the reproduction Roman glassworking 10), even if the glass initially appears in furnace by Mark Taylor and David Hill. The larger fragments could be recycled.

10 Case Study 1 identified, stratified contexts containing Sampling for evidence of glassworking waste were discovered, glass working which could be dated using a combination of documentary references and clay Glassworking furnaces, particularly pipes. Soil samples were taken from these early ones, rarely survive well and can be contexts, which were sieved and the difficult to identify as most large pieces of >2mm fraction was sorted. Large numbers glass were recycled. Sometimes the only of tiny glass threads were recovered and evidence for glassworking comes in the a proportion were analysed. This enabled form of small glass threads recovered from archaeologists to establish what types of samples taken during excavation glass were made at Silkstone and when (Fig CS1.1). (Dungworth and Cromwell 2006).

Medieval Whitby, North Yorkshire Whitby Abbey is the site of the monastery of Streaneahalch, founded in AD 656–7, and a later Benedictine monastery. During an English Heritage evaluation at the site, small fragments of glassworking waste were recovered from a posthole, which turned out to be part of an 8th- to 9th-century building (Jennings 2005). The sampling strategy for the subsequent Fig CS1.1 Processing samples on site at Whitby. excavation targeted the other features associated with this building, sampling during earlier excavations near the ruined 100% of posthole- and pit-fills and medieval Abbey, and the new evidence processing the samples on site using suggests that the plaques were made at flotation (English Heritage 2011) (Fig the site. CS1.2). Training was also provided in how to recognise glassworking evidence. Post-medieval Silkstone, South Yorkshire The glass recovered included reticella A coal-fired glasshouse was established rods made up of different colours of glass at Silkstone, South Yorkshire in the twisted together, small chunks of raw middle of the 17th century. Two trenches glass for melting, and assorted drips and were excavated in advance of works to lumps, none much bigger than 20mm. a building possibly associated with the A small glass plaque, decorated with glasshouse, one inside and one outside. Fig CS1.2 Pieces of raw glass (bottom), a 9.5mm long similar patterned glass rods, was found Although no glassworking structures were reticella rod (middle) and a glass plaque (top) from Whitby.

4.3.3 Deciding what to keep 4.3.4 Dating methods 4.4.1 Typological study Deciding what to retain from archaeological Archaeomagnetic dating has been used Specialists in archaeological glass can contexts is a complex issue, particularly successfully to date the last fi ring of provide information from examining on large-scale sites. The most important furnaces, where the fi red surface is fragments of excavated glass. Familiarity factors are the research questions specifi c undisturbed (Welch 1997; Welch and with a wide range of glass enables them to to the site being excavated; it is best to Linford 2005). This technique is at its use typological information to determine select material that helps to address these most precise for the post-medieval period date, original form and function, and questions. As a general guide, all evidence (Linford 2006). source of manufacture. The glass can from earlier, smaller sites, generally those Radiocarbon measurments can be provide further information about life on pre-dating the 15th century, should be obtained from single entity organic samples the site, such as who would have used the retained. Post-medieval and historic sites, (eg short-lived furnace fuel) (Ashmore glass and in what situations, the status of however, may be on such a large scale 1999; Bowman 1990; Waterbolk 1971). its owner, and the rarity and significance that this becomes impractical (see Figs 14 In addition, information on date can of the glass, both on the site and in a wider and 15 for example). If it is not possible to be obtained from documentary sources, context. Specialists will also advise whether retain all of the evidence, it is good practice by typological study of the glass and by scientific analysis of the glass would be to retrieve examples of the full range of scientifi c analysis of the glass or crucibles beneficial to address further questions. materials present and to estimate and (see sections 4.4 and 5.4, and Case Study 2). Many are independent researchers and can record the quantity at the site overall. Make be found by contacting the organisations sure that all types of artefact (crucibles, 4.4 Post-excavation analysis listed in section 10. wasters), deposit (raw materials, fuel Further scientific or typological waste, glass waste, cullet dumps, working investigation of the glass is usually 4.4.2 Conservation fl oors), context types and phases are warranted to help with the interpretation Much has been written on the condition represented in this sampling. and achieve the project aims. and deterioration processes of glass

11 (Newton and Davison 1996; Knight 1996; glass or to study weathering phenomena. Pollard and Heron 1996) and it is only SEM machine time can cost from £200 to summarised here (see also section 2.1). £800 per day (at the date of publication), The deterioration of buried archaeological depending on the analytical facilities (see glass can take different forms, such as below), but multiple glass specimens can weathering, lamination, pitting and probably be processed in that time. opaqueness; post-excavation deterioration If an energy dispersive spectrometer includes the formation of weathering crusts (EDS) is attached to an SEM, the glass can and, in the case of historical glass objects, be analysed for chemical composition at the ‘weeping’ or ‘crizzling’. same time. Only a small piece, a millimetre or more in size, is required. Using an EDS is 1 When glass weathers, the soluble one of the standard techniques for detecting components – such as sodium and the major constituents of glass, present potassium – are leached out, creating in amounts greater than 0.1wt%, but is physical stresses in the glass. The glass not suitable for detecting trace amounts contracts and splits into a series of silica- of elements. EDS facilities are likely to be rich weathering layers (lamellae) that included with the daily charge for the SEM. refl ect light unequally and appear as an iridescent weathering crust (see Fig 2). ICP 2 Corrosion and pitting can occur where There are several variations on the leached alkali becomes concentrated Fig 17 An X-ray (top) of a fragment of late 13th- to early inductively coupled plasma (ICP) on the surface in cracks or surface 14th-century, decorated, potash ‘forest’ glass, c 40mm wide, spectrometry method. ICP atomic from the evaluation at Chesterton Manor, Warwickshire, by scratches. The pH in the pit increases English Heritage. The X-ray reveals the decoration otherwise emission spectroscopy (ICP-AES) is a and the corrosion continues downwards. obscured by weathering and that the core of the fragment cheap (at the date of publication, £12 to White deposits – consisting, for example, is denser and better preserved than the edges (photo £20 per specimen) method of obtaining by David Adams and John Burnham of the Warwickshire of hydrated silica and sulphate salts – Archaeological Research Trust). compositional information for large might have formed in the pit (see Fig 6). numbers of specimens. For this procedure, 3 Weeping or crizzling glass is a 0.1g to 0.2g of glass is required per analysis, phenomenon of historic glass that shows (or worked) at a specific site. However, which is ground up and dissolved during as a network of fi ne cracks and/or an some glassworking waste is accidentally the process. The technique can detect oily fi lm or small aqueous droplets. It chemically changed by reacting with trace amounts (parts per million) of many is attributed to the chemical instability other materials, so it may not provide elements, usually about 20 at a time. This of certain types of post-medieval glass an accurate picture of the original glass information can help to answer questions (Kunicki-Goldfi nger 2008) (see Fig 4). composition. This is particularly true of of provenance and recycling, and to 4 As glass decays, any iron or manganese waste from within the furnace itself, and of differentiate between glass batches (see for present can oxidise in situ, making the glass adhering to fragments of crucible or example Jackson 2005). The preparation glass brown or black, and contributing furnace. Therefore moils, off-cuts and raw method used for ICP results in the loss towards its opacity (Knight 1996) (Fig 17). glass are generally the most useful types of silica, the main component of glass. of waste for establishing the type of glass However, the amount originally present The conservation of glass should be made and how this might have changed can be calculated, providing that all of the undertaken by an appropriately qualified from one batch to another. Glass waste other elements in the glass have been sought conservator (see section 10 on where to recovered from soil samples is likely to be and measured accurately; so including get help) following the principles outlined dominated by tiny fragments, but these can known standards is particularly important in the English Heritage Investigative still be used for analysis (Dungworth and for ICP work. ICP can also be used with a Conservation guidelines (English Heritage Cromwell 2006; Dungworth and Paynter mass spectrometer (ICP-MS), which is more 2008) and in texts such as Newton and 2006) (see Case Study 1). expensive but can measure even lower levels Davison (1996) and Tennent (1999). Diff erent analytical methods are used to of elements. Laser ablation (LA-ICP) can Conservation can include investigative investigate glass because they give varying be used to analyse very small fragments of conservation, cleaning, consolidation, types and levels of information, have wide- objects (a fraction of a millimetre) or even to reconstruction and repacking for long term ranging costs and need diff erent amounts obtain a result from the surface of a display storage. The level of conservation, and of material. With all analytical work, it is object with virtually no visible damage. how much of the assemblage is included, advisable to include standards of known depends on whether the glass is classed composition, to check the accuracy and TIMS as a bulk or as a small find, its condition precision of the analyses. Also, a large Mass spectrometry techniques, such as and the research questions posed. For number of glass specimens are more likely transmission mass spectroscopy (TIMS), example investigative conservation may to provide a statistically signifi cant answer are used for isotope analysis. Isotope include the use of X-radiography to record than only a few specimens would. measurements can help to indicate what the condition and any applied painted types of raw materials were exploited; decoration (Fig 17). SEM and EDS for example, the use of seaweed ash, sea Scanning electron microscopy (SEM) is shells and limestone have all been deduced 4.4.3 Scientifi c analysis used to look at objects at magnifications from strontium isotope data (see Case Scientific analysis often focuses on the of tens of thousands of times, for example Study 2). Neodymium isotopes have been composition of the glass manufactured to identify the tiny particles colouring increasingly used for provenance work

12 Case Study 2 in Britain over the past 700 years (Fig Determining the date of glass: CS2.1). windows The earliest window glass included in the project is 14th-century potash- The composition of glass depends on rich ‘forest’ glass, which contains high when it was manufactured, because the concentrations of potassium, magnesium ingredients used changed over time. A and phosphorus. The window glass of the recent English Heritage project has made later 16th and 17th centuries is usually a use of these chronological changes to high-lime low-alkali (HLLA) glass. From work out the probable date of window c 1700 until the fi rst few decades of the glass. Information from documentary 19th century almost all windows were sources about raw materials and recipes made from a mixed alkali glass with for window glass has been supplemented distinctively high levels of strontium oxide, with chemical analyses of historic window probably derived from the use of ash from Fig CS2.2 Portable XRF being used to analyse historic in-situ glass. This has established the distinct kelp (seaweed). The widespread use of window glass (undertaken adhering to safety protocols for using ionising radiation). glass compositions that have been in use kelp in the glass industry at this time is corroborated by documentary evidence. At the end of the 18th century, Nicholas LeBlanc developed a technique for converting common salt (sodium chloride) into sodium carbonate, and this cheaper, purer fl ux was used in British window glass from the 1820s. As a result, windows made after c 1830 are almost always soda-lime-silica glass with much lower levels of impurities, such as phosphorus, relative to earlier glass. The mechanisation of the window glass industry in the 20th century can also be traced in the chemical composition of the glass. Window glass can also be analysed in situ, using a portable X-ray fl uorescence (XRF) spectrometer (Fig CS2.2). The chemical analyses indicate the date of manufacture of individual historic Fig CS2.1 Chart showing how the concentrations of magnesium oxide in historic window glass vary over time, shown in years (AD) on the horizontal axis. Each diamond represents a window fragment and the error bars show the uncertainty in windows, better informing decisions on the date of that window. their conservation.

(see Case Study 3). Such analyses are more however, which aff ects how the results for are others, for example Neri, which date to expensive, at the date of publication from archaeological specimens are interpreted. the 17th century (Cable 2001) but which £150 to £250 for each glass specimen, and still describe processes that were widely can be complex to interpret, so projects 4.4.4 Treatises and historic archives used in earlier centuries. There are also some are best undertaken in collaboration with Technical treatises and historic archives references to glassworking in Roman texts an archaeological scientist specialising in can provide information for those aspects of (Freestone 2008; Price 2002, 81). that field. About 30mg to 50mg of glass are glassworking that leave little archaeological For more recent sites, technical textbooks, required for each analysis. evidence. For example our knowledge of such as Cable (2008), Muspratt (1860) and raw material collection and preparation, Pellat (1849), are good sources of detailed XRF and of the fritting process derives mainly information. In addition, paintings, X-ray fl uorescence spectrometry (XRF) is a from contemporary accounts (see section illustrations, engravings and photographs rapid and fairly cheap technique that can 3.2). Illustrations and photographs contain can be useful resources. Sometimes be used to determine the composition of information on the scale and deployment catalogues of wares produced by glass glass. A disadvantage of XRF is that it is less of the labour force and on working companies still survive (eg Miller 2007). sensitive for light elements, such as sodium conditions, as well as on details of A fuller summary of the types of records and magnesium, which are important equipment and processes. that are useful in investigating historic for characterising glass. However, a great Several early technical treatises on sites is given by Crossley in Dungworth and advantage is that portable XRF machines are contemporary glassworking traditions Paynter (2006). available (see Case Study 2), which can be have survived. The best known are those of used to analyse the surface of glass objects Theophilus, who wrote in the 12th century 4.4.5 Experimental archaeology and without damaging or moving them, for (Hawthorne and Smith 1979), and of ethnographic evidence example window glass or display objects. Agricola, who was active in the mid-16th Practicing glassworkers are able to comment Glass surfaces are often altered after burial, century (Hoover and Hoover 1950). There on archaeological glassworking waste; for

13 example, how particular types of glass Case Study 3 waste, or tool marks on artefacts, were made. Provenancing glass: Some glassworkers have experimented 1st millennium AD by using replica furnaces and with glass production and trade compositions similar to those of ancient glass (Taylor and Hill 2008). These The results from scientific analysis have experiments greatly aid the interpretation transformed our understanding of glass of archaeological glassworking features production in the 1st millennium AD. (Paynter 2008; Shepherd and Wardle Natron glass, made by heating natron 2009). Photographs from these experiments with sand, dominates during this period and online video clips are wonderfully (see section 3.1). Natron is a sodium- Fig CS3.2 A slab of failed glass made in a tank furnace informative (http://www.cmog.org/ rich crystalline material formed by from Bet She’arim, Israel. The slab is c 2m wide and weighs then go to ‘Glass Resources’, ‘Videos’ and evaporation of mineral-rich lakes like c 9 tonnes. Analysis suggests that it dates to around the ‘Glassworking Video Clips’). 9th century (photo by Jenny Price). those of Wadi Natrun in Egypt (Fig A variety of glassworking practices from CS3.1). It has been established that only shipwrecks; evidence of trade in raw glass around the world have also been documented. a small number of distinctive compositions during earlier centuries. As well as publications (Küçükerman 1988; of natron glass were in use across much of Large assemblages of natron glass Sode and Kock 2001), videos and photographs Europe and the Middle East during vessels and glassworking waste have now of glassworkers are increasingly available the Roman, and later, periods (for been analysed, focusing initially on on the internet. Ethnographic studies example Brill 1999; Freestone 2005; colourless and weakly coloured glass, include observations on attitudes, practices Jackson 2005). using techniques such as ICP-AES, and materials, including division of labour, This evidence means that there were ICP-MS and TIMS (see section 4.4). These seasonality and glassworking tools and probably only a small number of centres techniques can detect even trace amounts techniques, which can complement the making glass, in each case with a slightly of elements and the information has interpretation of archaeological fi nds and diff erent composition due to the make-up enabled archaeologists to determine documentary records. of the sand available there. The glass was where the raw glass came from. For made on a massive scale, then broken up example Freestone and co-authors 5 What you may fi nd: general and transported as lumps to workshops (Freestone 2005; Freestone et al 2008) indications of glassmaking across the Roman world, where the raw demonstrated that the greenish HIMT and working glass was shaped into objects. There is glass, commonly found in Britain from archaeological evidence to support this the mid-4th century, originates in Egypt. This section describes characteristic types model: large tank furnaces dated from the Analyses can also suggest how much of evidence indicating that glass production 6th to the 11th centuries AD have been recycling has taken place. The 7th-century and/or working took place at a site, the found in Israel and Lebanon, which could glass from Jarrow, Northumbria, is most common being: produce many tonnes of glass in each thought to have originated in the Levant, fi ring (Fig CS3.2). Chunks of raw glass although the levels of impurities suggest • furnace structures and fragments have also been recovered from Roman that it had been recycled many times. • crucible fragments • cullet dumps • raw glass • glass waste

Detailed examples of the waste produced by specifi c working methods are provided in section 6 to help with the interpretation of these fi nds.

5.1 Furnaces Only furnace types found in Britain are discussed here. There is no evidence from the Bronze Age or from the Iron Age for furnaces (see sections 8.1 and 8.2). Roman archaeological remains in Britain suggest the use of two furnace types. An early Roman furnace in London contained a built-in, tile-lined tank for holding the molten glass (Shepherd and Wardle 2009). The size and shape of the furnace is unknown, but it is likely to have had an ash pit and at least one stokehole for adding wood fuel to the fi re. In the later Roman period, however, it Fig CS3.1 Barnuj, one of the mineral-rich Egyptian lakes, with salts crystallising around the edge (photo by Ian Freestone). appears that the glass was held in ceramic crucibles or pots. The crucibles were seated

14 on a shelf or platform within a furnace (Cool et al 1999). This type of furnace continued in use into the early medieval period (Bayley 2000b). A replica furnace of this type is shown in Fig 18. Typical remains are an oval or circular, orange-fi red feature about 1m in diameter, sometimes tile-lined, which is the remains of the ash pit. Fragments of vitrifi ed or fi red furnace superstructure are also sometimes found. These generally have a glassy surface on the inside owing to reactions with the corrosive furnace gases or spills of glass. Similar pot furnaces, round or oval in plan, were used in the early medieval period. Furnace remains at Glastonbury, Somerset – of Middle Saxon date – consisted of ash pits, 0.9m to 1.2m in diameter, incorporating reused pieces of Roman tile, with partial remains of clay walls along the edges (Bayley 2000a). Stone was used around the furnace base and at the stokehole entrance. The furnaces might have had a domed superstructure and had been rebuilt several times. Fig 18 Reproduction Roman glassworking furnace made by Mark Taylor and David Hill, c 1.5m external diameter, showing the Medieval and post-medieval furnaces domed superstructure with two of the three gathering holes (one open), the marver (raised block on the right), blowing irons had a diff erent type of design. They are with ends heating (centre front) and fuel pile at the rear. typically rectangular in plan – 3m wide and between 4m and 5m long. There are two parallel platforms known as sieges on either side of a central ground-level fi re trench, all of which often survive archaeologically (Figs 19 and 11). A fi re was set at the end of the trench and the crucibles sat on the sieges. Late medieval furnaces are generally stone built, whereas post-medieval ones make more use of refractory brick, which was not available earlier. A coal-fi red furnace for melting glass was developed in the second decade of the 17th century. A patent for manufacturing glass using coal was granted to Sir Robert Mansell and a royal proclamation issued, which banned (in England) the use of wood fuel in glass furnaces. This had implications for the location and design of glass furnaces (Crossley 1990, 2003). The earliest coal-fi red furnaces retained the two parallel sieges with a central fi re trench, but the base of the trench was made c 1m below ground level, so is sometimes referred to as a fl ue. The fi re was typically supported above the trench on iron bars placed mid-way along it (eg Pellatt 1849, 57). The changes were necessary because coal requires a greater draught to burn eff ectively, produces a shorter fl ame than wood and leaves much more ash. The subterranean fl ue ensured that suffi cient air reached the fi re and allowed the ash (and clinker) to collect where it would not restrict the fl ow of air. Partial remains Fig 19 The remains of a 16th-century glass furnace at Little Birches, Wolseley, Staffordshire, looking along the fi re trench with of the underground fl ues often survive glass coated sieges on each side, where circular impressions from the bases of the crucibles remain (photo by Chris Welch).

15 Hot gases exited the furnace through prevented any unreacted batch from small fl ues positioned over the crucibles, passing into the working end. passing into the cone. There were up to 10 gathering holes in the furnace walls, one 5.2 Annealing structures for each pot. Annealing is described in section 3.6. This The coal-fi red glass industry thrived in process sometimes took place in a dedicated the areas of Lancashire, Tyneside and the part of the main furnace (see Fig 13), and so West Midlands. Later an important industry little specific evidence is likely to survive. became established in Manchester, with Some examples of stand-alone more than 25 glassworks in operation by annealing structures have been proposed, the 1870s (Miller 2007). such as at the 16th-century glassworking The furnaces were accompanied by site at Knightons (Wood 1982), where many ancillary buildings, such as annealing quantities of large window glass fragments sheds, cutting and engraving workshops, were found associated with a fi red feature offi ces and warehouses (Miller 2007). A near to the glass furnace. This was thought number of cones have been excavated (eg to be an oven for annealing window Ashurst 1970) and the fl ues and evidence glass crowns (see section 6.3). However, of the sieges often survive. Sometimes fl ue as annealing did not require very high Fig 20 The 18th-century cone at Catcliffe, Yorkshire. entrances can be seen in the walls of temperatures, such structures are rarely nearby canals. identifi able archaeologically. archaeologically (Crossley 1990; Tyler and Regenerative glass furnaces were Continuous lehrs, used from the 19th Willmott 2005) (see Fig 13). developed in the 1860s. These were still pot century, are more substantial; there can be The characteristic conical furnace furnaces, but achieved higher temperatures archaeological evidence of a brick structure cover building appears to be a late 17th- and used gas fuel. The gas was normally and, if the fl oor survives, perhaps rails or century to early 18th-century development produced in gas ovens at the glassworking grooves remaining from the system used (Crossley 1990; 2003). The earliest site itself, and the remains of these structures to move the glass through the lehr (Cable surviving cone, dating to 1740, is at can be expected (Fig 22). The regenerators 2008; Miller 2007) (Fig 24). Catcliff e, Yorkshire, and is 18m high (Fig comprised brick-fi lled chambers, connected 20), but some were taller. They are typically by valves to the incoming and outgoing 5.3 Fuel waste between 12m and 15m diameter at the furnace gases (Fig 23). The hot furnace Wood was the principal fuel used to heat base. The cone was essentially a chimney, exhaust gases passed heat to the glass furnaces until the 17th century, so covering the furnace and working area. The regenerators, which then preheated ashy or charcoal-rich deposits are often fi re was set in a fi rebox at ground level, with incoming combustion gases, making the found at glasshouse sites. In such furnaces air supplied through subterranean fl ues furnaces much more effi cient (Crossley corrosive gases from the wood fuel reacts (Fig 21). The tall cone helped to induce a 2003; Krupa and Heawood 2002). with the furnace walls to make a glassy strong draught to feed the furnace fi res, and In the 1870s, continuous tank furnaces layer on the inside surfaces (see Fig 11). also to remove the fumes generated. were introduced that produced better- Droplets of this bluish glassy material The fl ames and heat entered the furnace quality glass more cheaply. The furnace was are found at furnace sites and are easily through a hole, or ‘eye’, in the centre of the charged with raw materials at the ‘melt end’ confused with intentionally made glass. fl oor and were drawn towards the crucibles, and the molten glass was drawn off at the From the early 17th century, furnaces which were set in a circle around the eye. ‘working end’. Floating bridges in between were coal-fi red. The vitrifi ed coal ash

Fig 22 One of a bank of 19th-century gas producers Fig 21 An 18th- to 19th-century glass cone under excavation at Dudley Flint Glassworks, Stone Street Square, West Midlands excavated at the Powell and Ricketts glassworks in Bristol (Birmingham Archaeology and Dudley MBC). (photo by Ian Miller).

16 formed clinker, amorphous lumps of which can be found in large quantities on glasshouse sites. Clinker is formed wherever coal is burned, so is not restricted to glasshouses. It is dark coloured, light in weight and vesicular (Fig 25). Gas-fi red furnaces were used from the 1860s (see section 5.1).

5.4 Crucibles Crucibles, also known as ‘pots’, are the ceramic containers used to hold molten glass. Crucibles were used for most glassworking before the late 19th century. Many crucibles, especially late medieval and post-medieval ones, are extremely robust and so crucible fragments are common field-walking finds. They are usually fragmentary and the inside surfaces sometimes have a glassy layer on them. Lead-rich glass layers usually survive Fig 23 (above) The remains of an early regenerative furnace excavated at the Powell and Ricketts glassworks in Bristol well but other types of glass tend to spall (photo by Ian Miller). off in chunks, leaving a pitted, and often bleached, inner surface to the crucible. If only a thin layer of glass survives on a crucible, its composition will have been significantly affected by the dissolved ceramic, and this fact must be taken into account when undertaking or interpreting analyses. Crucibles were also used for metalworking, but it is possible to tell them apart (see section 7). Crucible size, shape and fabric vary over time, and these characteristics can indicate the date of glassworking activity (Fig 26). Roman and early medieval crucibles tend to be of contemporary pottery forms (Fig 27), and can be identifi ed by the coating of glass surviving on the inside surface. The Roman and early medieval examples recovered mostly contain pale blue or green natron glass, although some crucibles used for Fig 24 (above) The entrance to the lehr at Red House Cone, Stourbridge, West Midlands; the stoke holes are at the bottom of melting yellow and white glass have been the image and the trays of glassware on the upper level, in the tunnel. found from 3rd- to 6th-century contexts (Bayley 2000a, 2000b; Cool et al 1999). Medieval crucibles used for melting lead glass are known from Gloucester, Lincoln and York, dating from the 10th and later centuries (Bayley and Doonan 1999; Bayley 2000b). Contemporary Stamford Ware bowls were used in York (Fig 28), but custom-made vessels were used in Lincoln and Gloucester. After the 10th century, when plant ash glasses came to dominate, higher temperatures were needed to melt the glass. Medieval and post-medieval crucibles were made especially for the purpose, from clays that were known to be temperature resistant. Examples from the 13th to the 16th centuries have sandy fabrics and are greyish in colour, becoming paler towards the surface. They often have glassy coatings on Fig 25 Clinker from the 17th-century coal-fi red glasshouse at Silkstone, South Yorkshire; the pile is 180mm wide.

17 Fig 26 Crucibles through the ages: 1 Roman crucibles from York, 2 middle Saxon crucibles from Glastonbury, 3 late 10th- to early 11th-century crucibles for lead glass from Flaxengate, Lincoln, 4 mid-14th-century crucibles from Blunden’s Wood Surrey, 5 early 17th-century crucibles from Kimmeridge, Dorset (illustration by John Vallender). both the inner and outer surfaces, due partly outer surface, diff erent from the blue- 5.5 Frit to the glass they contained and also caused green, glassy outer surfaces typical of Although fritting is known to have taken by reactions with the corrosive furnace crucibles from wood-fi red furnaces. place (see section 3.2), frit is rarely found atmosphere. These crucibles tend to be By the 19th century most crucibles archaeologically. This is not surprising, as bucket- or barrel-shaped and are c 0.3m were made using refractory Stourbridge such a friable, partially reacted material to c 0.5m tall. Examples are known from clay and were massive, standing 1.4m would be unlikely to survive (Paynter and Staff ordshire (Crossley 1967; Welch 1997) tall. Crucibles used to melt lead glass in Dungworth forthcoming). Crystalline, and from the Weald (Kenyon 1967) (Fig 29). coal-fi red furnaces were made with lids or amorphous lumps of waste from By the end of the 16th century white- integral covers to prevent fumes from the glassworking sites are common, but these fi ring, chemically resistant clays were fuel spoiling the glass (Fig 30). are often lumps of chemically altered glass, specifi cally sought for glass crucibles. Sometimes atypical crucibles are found which cannot therefore be recycled and so Previously used crucibles were also ground that are smaller than most others from the were discarded (section 5.8). At Vauxhall up to make ‘grog’, which was added to same site. These generally contain residues glasshouse, London, however, some the clay used for new ones (Paynter of brightly coloured glass (Kenyon 1967), partially reacted glassy material survived forthcoming). These grog particles can be which was required in smaller amounts. (Tyler and Willmott 2005). seen in broken sections using a low-power These pots, sometimes known as ‘piling microscope. Crucibles from coal-fi red pots’, were set on top of larger crucibles in 5.6 Cullet furnaces have a more matt brown to purple the furnace. Cullet dumps (see section 3.3), made up of glass for recycling, are one of the most useful resources for understanding a glassworks, as they can contain large amounts of diagnostic glass waste, including fragments of broken products. Cullet assemblages need to be interpreted with caution, however, as not all the glass was necessarily made at the site; in most periods glass for recycling was traded across large distances. Chemical analysis can help to establish the type of glass made

Fig 27 (top) Saxon crucible fragments from Glastonbury Abbey, Somerset, used to melt pale blue-green natron glass; the rim fragment is c 65mm wide. Fig 28 (above) A 10th- to11th-century crucible from Coppergate, York, c 150mm in diameter, containing traces of lead glass. Fig 29 (right) A large crucible fragment from an early 16th-century wood-fi red furnace at Bagot’s Park, Staffordshire Fig 30 (above)19th-century closed crucibles, which (photo by David Crossley). were c 1.4m tall (from Muspratt 1860).

18 at the site, by identifying a common glass composition among waste and fi nished items (Dungworth and Cromwell 2006).

5.7 Raw glass In earlier periods, chunks and lumps of raw glass were imported and brought to glasshouses for melting, and these are also sometimes found. They are of variable size, but have fracture surfaces where they have been broken from larger masses when cold (Fig 31). Very rarely, large fl ows or blocks of glass that have cooled in the furnace or ash pit are found.

5.8 Waste glass Much of the glass recovered from glassworking sites is an assortment of lumps and trails (see Fig 2); very small, fi ne trails are often described as threads. There may Fig 31 Fragments of raw Roman soda-lime-silica ‘natron’ glass excavated at Basinghall Street, London; the width of the top be tool marks at one end. This glass waste fragment is 128mm (photo by Andy Chopping/MOLA). is helpful in indicating that glassworking took place and can be useful for scientifi c analysis, to help establish the composition of glass being made at the site (Dungworth and Cromwell 2006). However, lumps and trails are not often diagnostic of the type of glassworking that was undertaken. Glass lumps, trails and threads are dropped around the furnace during glassworking (Fig 32). Experimental work (Taylor and Hill 2008) suggests that the highest concentrations are likely to be found near the gathering holes (see Fig 16). While larger trails were recycled, Fig 33 smaller ones were trampled into the (above) Roman glassworking waste from London, formed when inclusions were removed from the glass; working surface. Tiny threads of glass are the length of the top fragment is 58mm (photo by Andy thus often present in fl oor layers and in Fig 32 Trails of glass from Belmont Row, Birmingham, Chopping/MOLA). dumps at glassworking sites, but, because excavated by North Pennines Archaeology; the longest pieces Fig 34 (below) Late 17th- to early 18th-century glass bottle are c 30mm. Waste from the production of colourless lead waster from Lime Kiln Lane, Bristol (7.5mm wide). Originally of their size, are only recovered from glass is often pale green due to contamination, and may transparent green, this HLLA glass has turned opaque processed soil samples (Dungworth and contain tiny visible droplets of metallic lead. cream/blue after prolonged heating and exhibits dichroism. Cromwell 2006) (see Case Study 1). Sometimes the glassworker would been chemically changed by reacting with spot an inclusion in the gather of glass the fuel ashes and furnace gases, or with and would hook it out with a tool, so an the materials used to construct the furnace inclusion can be seen at one end of some or crucibles. This is sometimes apparent by glass trails (Fig 33). the diff erent colour or opacity of this glass Occasionally ‘wasters’ (products that relative to the majority of the assemblage, have gone wrong) survive at glassworking and by the presence of bubbles or crystals. sites, although these are generally Because of its strange appearance, this type fragmentary, distorted and discoloured of material is sometimes misidentifi ed as by heat. Even though these wasters are specifi c types of production waste, such not chemically changed, the appearance as frit (see sections 3.2 and 5.5). The fi nal of the glass can be drastically altered. In appearance of the altered glass depends on particular, the transparent green, lime-rich its original type and what has happened (HLLA) glass typical of the post-medieval to it. Altered HLLA glass often turns from period sometimes becomes opaque and transparent green to an opaque blue or dichroic, as in Fig 34. cream colour, and is sometimes dichroic Glass that has fallen into the ash pit, (Fig 35). Altered lead glass may turn from fi re trench or fl ue of a furnace also tends to colourless to pale green and, although it have an altered appearance, either because generally remains transparent, small silvery of the temperatures and atmosphere to droplets of metallic lead often form which it has been exposed, or because it has (see Fig 32).

19 Altered glass waste was not suitable for 5.9 Tools with the aid of a central former, such as a recycling as it would contaminate the batch. As with other crafts, glassworking tools (Fig wooden or metal rod, which could be used Altered glass is not suitable for analytical 36) are rarely found on archaeological sites. to perforate, and then enlarge, a hole in a work where the aim is to establish the Valuable metal tools are unlikely to have blob of glass. Alternatively, softened glass original composition of the glass. been discarded and wooden tools would was wound around the wooden or metal not survive. There are occasional examples, rod and the glass ends joined (Hawthorne however, such as the post-medieval blowing and Smith 1979, 73–4). iron found at Bagot’s Park (Crossley 1967). 6.1.2 Core forming 6 Interpreting fi nds: the evidence Core forming was an early method of from different glassworking methods shaping glass vessels and objects, for example making beads in the Bronze Age The basic principles of glassworking and and in the Iron Age. Softened glass was some general forms of archaeological shaped around a core, for example of evidence have been described in sections 3 tempered clay, which was later broken-up and 5. This section describes in more detail and removed to leave the inside hollow. diff erent methods of forming glass objects, with particular emphasis on the types of 6.2 Vessels and bottles

Fig 35 Opaque cream-blue waste from the 17th-century waste produced by each method and any 6.2.1 Free blowing glassworks at Silkstone, South Yorkshire; each fragment is characteristic evidence left on the glass The fi rst evidence of glass blowing in Britain 10 to 15mm wide. object itself. dates to the 1st century AD, and the technique has been widely used since (Price and Cottam 6.1 Beads, bangles and counters 1998; Shepherd and Wardle 2009). 6.1.1 Hot shaping A blob or gather of hot glass was Simple objects like gaming counters collected on the end of a long metal pipe could be formed by heating small blobs known as a blowing iron. The glassworker of glass, or sections from glass canes, on a blew down the pipe to infl ate a bubble in fl at surface until the top surface rounded the glass (Fig 37). The bubble of glass, naturally. The base could be fi nished by known as a ‘paraison’, was shaped further grinding. Rings and bangles were made using tools (see Fig 36) to constrict some areas, or by blowing to expand others. While shaping an object, glassworkers often roll it over the fl at surface of a stone block, known as a ‘marver’ (Fig 37), or rotate it in a hollow wooden former. When blowing certain types of vessel, like wineglasses, the glassworker needed to pinch the end of the gather to form the bottom of the wineglass bowl (Fig 38). This Fig 36 19th century glassworking tools (from Pellat 1849). formed a small protrusion, known as the paraison end, which was cut off . These look Fig 38 A glassworker removes the paraison end: the rounded knob to the left of the pincers. like a marble with a pinch on one side. The part of the vessel attached to the blowing iron becomes the neck or rim of the vessel, while the infl ated glass bubble generally becomes the body of the vessel. It could be left with a rounded base, as on a fl ask or palm cup, or the base could be pushed in to make a more stable ‘kicked’ base (Fig 39) or a foot-ring. All the while, the object remains attached to the blowing iron, so that it can be repeatedly returned to the furnace and reheated. Glass could be added to the semi-formed object while it was still on the blowing iron, for example decoration in the form of trails of glass, or ‘prunts’ (cone- shaped protrusions of glass). Sometimes glass was applied to the vessel base to form a foot-ring or base-ring to make it more Fig 37 Glassworker William Gudenrath infl ating a glass bubble stable or for decoration. with the experimental furnace (by Mark Taylor and David Hill) Fig 39 A blown vessel, still attached to the blowing iron, with to the right and the marver in the foreground. The bubble has a kicked base, from the experiments by Mark Taylor The glassworker removed the blowing ribbed decoration that was obtained using an optic mould. and David Hill. iron by weakening the glass at the point

20 Fig 40 A Roman moil from London, showing a stepped profi le, c 13mm diameter (photo by Andy Chopping/MOLA).

Fig 42 Glassworker Mark Taylor detaches the neck-end of a vessel from the blowing iron. The vessel is supported by the pontil iron attached to the base. The furnace is at the rear and the marver to the right.

Fig 41 A long moil from Basinghall, London, with black specks and streaks caused by iron scale from the blowing iron, c 36mm tall (photo by Andy Chopping/MOLA). where it was attached to the iron, for example by fi ling a groove in the glass or by dropping a spot of cold water there. A sharp tap then broke the object from the iron. The collar or cylinder of glass left on the Fig 44 (above) Reproduction wavy ribbons of glass; the blowing iron is generally known as a ‘moil’, longest is 130mm. Fig 45 (below) The base of a small post-medieval jug from although other terms, such as ‘knock off ’ or Shinrone, Ireland, made of green HLLA glass with a pontil ‘rod end cullet’, are sometimes also used. scar in the centre and iridescent weathering of the surface Moils are a useful indicator of glassblowing. (45mm diameter). Moils are ideally suited for analysis in order to determine the glass composition. Some of the Roman moils from London have small crizzled areas that indicate the use of water to weaken the glass there (Shepherd and Wardle 2009), and have a stepped profi le on the opposite side (Fig 40). Moils have diff erent lengths and shapes, in part depending on the type of object Fig 43 Formation of wavy ribbons in a mid-18th-century being made. Distinctive lid moils are from illustration of goblet production by Diderot (from Gillispie the production of particular vessel types, (ed) 1959). where the moil was cracked off when the vessel was cool and the rim cold-fi nished If the object was going to need more Handles were applied last, to an by grinding (Shepherd and Wardle 2009). hot working, then before it was removed otherwise completed vessel (see Fig 12), Alternatively, the moil could be removed from the blowing iron another iron called usually while it was on a pontil. When by dunking it into cold water. Surviving the ‘pontil iron’ or ‘punty’ was attached to working was fi nished, the pontil was moils of this type are usually crazed – the object at the base, using a small blob of detached leaving a diagnostic round completely covered in a network of fi ne glass to secure it (Fig 42). scar on the base (Fig 45), although on cracks from being cooled quickly – and Once attached to the pontil, glass could post-medieval fi newares such scars were others are fragmented beyond recognition. be trimmed from the rim of the vessel using removed by grinding. Sometimes moils have black fl akes of iron shears, for example to level the edge of a oxide on the inside surface, which is scale wineglass bowl. These strips of glass have a 6.2.2 Mould blowing that has detached from the blowing iron. wavy appearance (Figs 43 and 44). Vessels and objects could be blown into Occasionally, longer moils were produced, The object was reheated by re-inserting a reusable mould, transferring the shape for example if there was an impurity or it into the furnace through a gathering hole, and decoration of the mould to the glass bubble in the glass near the blowing iron, so that the rim softened and could be shaped paraison when it was infl ated within the the glassblower could detach the vessel at further (see Fig 1); reheated rims became moud. Moulds are known from the Roman a more distant point so that the blemish smooth and ‘fi re rounded’. Other types of rim period, most often made of clay, but remained in the moil rather than being in were made by folding; spouts could be shaped sometimes of stone, wood or metal (Foy the fi nished object (Fig 41). and handles attached to the rim. and Nenna 2001; Price 1991). Moulds of

21 several pieces were used for vessel forms 6.2.4 Casting and slumping Cylinder glass was made in Britain from that could not be removed intact from a Experimental work by Mark Taylor and the 19th century, using a variation of the single-piece mould. Use of a multi-piece David Hill has shown that forms such broad-glass method. Longer cylinders, and mould resulted in an object with seam as Roman ‘cast’ bowls might have been therefore larger sheets, of glass were made lines where the mould pieces joined. The made by slumping the glass over a convex by swinging the cylinder during blowing vessel could be fi nished in a similar way mould. A gather of glass was pressed on so that it further elongated under its own to free blown vessels (above). Mould a fl at surface to form a disc, which was weight, for example by standing on steps or blowing was used to create decorative then placed over a hemispherical mould alongside a swing pit. At Pilkington’s 19th- fi ns on medieval goblets (Tyson 2000) and reheated so that it sagged into shape. century glassworks, swing pits c 2.5m deep and to make decorative stems for goblets Thin slices from preformed multi-coloured, survived at the working end of the furnace. (Willmott 2002). patterned glass canes could also be fused The cylinder was allowed to cool before In later periods, more complex and robust together to form the initial disc, but with being scored or cut and then was reheated in moulds were developed, made from an elaborate pattern in the style known as order to open it out; cylinder glass retained iron or copper alloys and hinged. Initially, millefi ori ‘a thousand fl owers’. a better fi nish on the bottom surface than the moulds were for shaping the base of post- broad glass because of this process. medieval bottles, but in the 19th century 6.2.5 Pressing glass glassmakers developed a series of multi-piece Pressed glass was manufactured by placing 6.3.2 Crown glass moulds, used for mass production, which an appropriate-sized lump of molten glass Crown glass was produced by blowing a shaped the complete bottle. The most famous in a hinged cast-iron mould (Cable 2008; spherical bubble of glass, transferring this of these was the cast iron three-part mould Pellatt 1849). This process was used to to a pontil and then spinning it until the patented by Ricketts in 1821, which enabled produce a wide range of simple vessel forms centrifugal forces caused the glass to fl are the production of the body and neck, as well – which could nevertheless have complex out and expand into a large disc (Fig 48). as decoration, from the one mould. decoration – and objects such as cathode Crown glass did not need fl attening and However, the glass was still infl ated by a ray tubes (Fig 46). Pressing was introduced so tended to have a superior surface fi nish glassworker blowing down a blowing iron; in the early 19th century and was used to compared to broad glass. Crown glass could the mechanised production of bottles, using produce vessels in imitation of cut glass. also be produced thinner than broad glass, compressed air, did not become widely which helped to improve its transparency. adopted until the 20th century. 6.3 Windows and fl at glass However, crown glass had two draw backs: 6.3.1 Broad and cylinder glass the central portion where the pontil was 6.2.3 Optic blowing Broad glass (also known as ‘muff glass’) attached, called the ‘bull’s eye’, was thick A gather of glass could be partially infl ated was made by blowing a bubble of glass, and so discarded; and the general shape of in a mould to transfer a pattern onto the elongating this into a cylinder shape, crown glass meant that only small panes of gather. Stone moulds are known but other removing both ends and then cutting the glass, known as ‘quarries’, could be cut from materials, such as metal, would also be cylinder along its length while it was hot the disc. Like broad glass, crown glass had suitable (see Figs 10 and 37). The vessel was (Fig 47). The cut cylinder of glass was then subtle imperfections, such as a slight curve completed by free blowing, so that the fi nal fl attened on a stone or metal surface to or wave, which tended to distort the view pattern had a fl owing, distorted appearance. produce a rectangle or square of glass. This through the fi nished glass. This technique was used in the Roman took place while the glass was hot so the There is unlikely to be much evidence period, and was also used to produce fl uting bottom surface tends to be slightly rough, at a glassworks to indicate crown glass (vertical ribs) and other designs on early although this could be improved by grinding production, as the crowns were cut to size medieval and post-medieval vessels (Evison and polishing (see section 6.4.3). Broad glass by a glazier at the point of use. However, the 2008; Tyson 2000; Willmott 2002). windows were made from the 3rd century. remains of broken crowns have been reported

Fig 46 (above) Removing the glass cone for a cathode ray tube from a hand press, comprising a plunger and mould, at Osram glassworks, Newcastle upon Tyne, mid-20th century (reproduced by permission of English Heritage.NMR). Fig 47 (right) Broad glass production shown in a mid-18th- century illustration by Diderot (from Gillispie (ed) 1959).

22 commonplace from the 1930s (Cable 2004; 6.4.4 Cutting and engraving Krupa and Heawood 2002; McGrath and Wheel engraving made use of a rotating Frost 1937). wheel, made of stone, copper, wood or iron, with an applied abrasive, such as pumice, 6.4 Decoration emery, corundum or diamond, to engrave 6.4.1 Applied glass decoration the glass. Diff erent wheel profi les were Additional glass, often in diff erent colours, used to create diff erent eff ects, for example could be applied as decoration. Hot glass fl at, curved or v-shaped cuts. Wheel-cut was trailed onto the surface of vessels (Fig glass was decorated by patterns of linear 51) or used to make prunts. Beads and other cuts or abrasions or with deeper circular or

Fig 48 Spinning a crown of glass in a mid-18th-century objects were also decorated in this way. illustration by Diderot (from Gillispie (ed) 1959). A glass gather could be rolled into blobs or chips of glass, frequently of from some sites. These might be identifi ed diff erent colours, which were then often by bull’s eyes and disc rims (Fig 49). The size ‘marvered’ into the surface (see section of the glass discs increased over time, from 6.2.1). Preformed canes or rods of glass in medieval examples of about 0.7m diameter contrasting colours could be applied to the up to 1.4m by the mid-19th century. The glass surface to make a design. These canes edge might be slightly thickened, and there were sometimes patterned, made from might be discernable concentric markings or diff erent colours of glass twisted together bubbles on the glass (Crossley 1990). or from a rod with contrasting colours trailed onto it (reticella) (see Case Study 1, Fig 49 Bull’s eyes used decoratively in glazing. 6.3.3 Cast glass Fig CS1.2) (Willmott 2002). Some Roman window glass was made by Thin trails of glass or patterned rods pouring molten glass onto a surface and have been found at glassworking sites then using tools to manipulate it into an (Bayley 2000a; Jennings 2005), but approximate square. The resulting pane such fi nds are often very small, and so often has an irregular thickness, with are frequently only recovered during the a rough, matt underside and a smooth processing of environmental samples. Rods upper side (see section 8.3.3). Casting was are sometimes distorted at one end with a again used for window glass from the 18th straight-edged impression from where the century, for making cast plate (see below). glass was gripped with pincers.

6.3.4 Plate glass 6.4.2 Impressed decoration Plate glass usually refers to large panes of fl at Various techniques were used to impress glass with a good quality polished surface. patterns onto glass. Stamps were sometimes Blown plate glass was produced from the applied to blobs or prunts of glass while early 17th century, and was made by making it was hot, for example on jug handles. thicker than normal broad glass and then Tools, such as rasps, fi les, toothed wheels or polishing it. It was expensive and used rarely. pincers were used to impress patterns into Cast plate glass was made in Britain applied trails or rings of glass on medieval from the later 18th century. Molten glass vessels (Tyson 2000). was ladled from the furnace onto an iron casting table and then rolled into large fl at 6.4.3 Polishing and grinding sheets, which were subsequently ground Many glass objects were fi nished by some and polished in a number of stages on form of polishing and grinding, for example both sides (see section 6.4.3) (Krupa and to remove tool marks or to fi nish the surfaces

Heawood 2002) (Fig 50). The initial sheet of moulded or cast objects. Evidence of Fig 50 Transparent, fi nished cast plate glass (top) compared to of glass was made considerably thicker than this is sometimes visible on objects and is partially ground cast glass, which appears matt, from excavations usual to allow for losses during the grinding mentioned in some documentary sources, at the site of the Thames Plate Glass Company, London. process (Louw 1991). but is diffi cult to identify in an archaeological In the late 1830s an improved polishing context. Fine, hard materials, such as sand, technique was developed, in which large ground glass, emery or pumice, were used thin sheets of glass made by the cylinder as abrasives. Iron oxide powder was used to process could be polished without breaking obtain a polish in the 19th century. by supporting them on a thick bed of wet The term ‘plate’ glass usually refers to leather. The product, called ‘patent plate’, was polished fl at glass, which was used when much cheaper to produce than cast plate. larger panes with a good surface fi nish were required, for example mirrors, coach 6.3.5 Mechanised drawing windows and, later, lighthouse windows and In the early 20th century glassmakers shop fronts (see section 6.3.4). This polishing Fig 51 Applying hot glass from a gathering iron to a vessel developed a mechanised method of was initially done by hand, but steam power surface, forming a decorative trail, from the experiments by drawing of glass, which became was used increasingly from the 19th century. Mark Taylor and David Hill.

23 quality colourless English glass from the Blast-furnace slag is also easily mistaken late 16th century to the early 18th century for intentionally-made glass. In terms of its (Charleston 1984). Stippled glass engraving composition it is similar to post-medieval lime- was developed in the 18th century. rich (HLLA) glass, so has a similar range of blue-green colours and density, but is opaque 6.4.5 Painting, staining, fl ashing (Fig 56). Blast-furnace slag can also exhibit and enamelling the unusual creamy opacity and dichroism

Fig 52 Fragment of a colourless Roman glass tray or plate from The best known application of painted, seen in post-medieval glass (see section 5.8). Binchester, County Durham, with cut facets, c 80mm wide. stained and fl ashed glass is for decorative In addition, blast-furnace slag tends to be windows, from the medieval period richer in iron than deliberately-made glass and onwards. The study of stained glass is a sometimes contains small metallic droplets. It large subject area, only briefl y described is often more bubbly than typical glass waste here, but further information can be and is most likely to be found as large angular obtained from some of the organisations chunks (Bayley et al 2001). listed in section 10. The production of medieval stained glass 7.2 Other high temperature processes panels began with a full size drawing of the Glassy materials are common accidental design. This template guided the selection, by-products of many high temperature cutting and decoration of diff erently processes. Accidentally produced glass can coloured pieces of glass. Pigment was Fig 53 Sections through two types of medieval red fl ashed painted onto the glass to create dark lines. glass from York Minster: top, Chapter House; bottom, Great East Window, in each case magnifi ed c 10x with the Silver stains were used to produce diff erent colourless base window glass at the bottom (photo by Jerzy shades of yellow (see Fig 17). The glass Kunicki-Goldfi nger). pieces were then heated to fuse the pigment in place and develop the colour of the stain. Red glass had an intense colour, so a sheet of red glass would be too dark. To obtain a less intense shade, a thin layer of red glass was ‘fl ashed’ onto a sheet of colourless glass (Fig 53). Further decorative eff ects could be created by selectively abrading or etching away the coloured glass, revealing colourless glass beneath, which was most commonly oval facet cuts (Fig 52). Wheel-cutting was done in the 19th century. also used for intaglio engraving, in which Examples of enamelled glass vessels a design was cut into the glass; for relief are known from the Roman, medieval engraving, in which heavy cutting resulted and post-medieval periods, although such in a design that protruded from the surface; pieces are rare. Fig 54 A Roman metalworking crucible from Dorchester, and for cameo glass, in which the design Dorset, 120mm high. The glassy material is more likely to be concentrated on the rims and outer surfaces of a metalworking was in relief in a contrasting glass colour 7 Materials mistaken for crucible. Crucibles used for metal melting are always to the base glass. Heavier wheels, such as glassworking waste reduction-fi red. stone, and coarser abrasives were used for cut glass, particularly the initial rough 7.1 Metalworking waste cutting (Dreiser and Matcham 2006). Ashes from charcoal fuel used in metal- In the Roman period wheel cutting was working react with any siliceous material common and sometimes elaborate, although to make an accidental glass, as happens on relief-, intaglio- and cameo-cut designs were glass furnaces and crucibles. Glassy layers rare. Cut decoration was again popular are often found on metalworking crucibles during the 18th century. Initially, wheel- (Fig 54), and these can be particularly cutting was used for inscriptions, scenes misleading , as traces of the metal often give and portraits, in a similar way to point the glassy layer a striking colour; for example engraving (see below). Geometric patterns the presence of copper oxide produces red Fig 55 Roman crucible containing red glassy silver-refi ning became popular in the later 18th and early or blue-green (Bayley et al 2001). waste from Chichester, West Sussex, 30mm wide. 19th centuries, but heavily cut glass declined Lead-fl uxed glasses were formed as by- in popularity from the mid 19th century, products of processes such as silver refi ning coinciding with the increased production of or lead smelting (Fig 55). These by-products pressed glass (section 6.2.5). could be discarded or re-cycled, but in some Point engraving used a tool with a fi ne instances the glass was used. For example hard tip, such as a diamond, fl int or steel to waste slag from silver refi ning was used for make linear or stippled designs, the latter red enamel in the Iron Age (Bimson and producing a shaded eff ect using dots. Linear Freestone 2000), and waste slag from lead engraving was known, although rare, in the smelting was used to make early medieval Roman period, but became popular on high- linen smoothers (Gratuze et al 2003). Fig 56 Blast furnace slag.

24 be misinterpreted as evidence of intentional same general type (soda-lime-silica natron glass production or glassworking. Some glass) as the glass artefacts from Iron types of plants, when burned, produce ashes Age sites, and contains many of the same with just the right proportions of silica and colourants and decolourisers. alkali fl uxes to make a glass. The ashes of Archaeological evidence for secondary wood or charcoal fuel can react with the glassworking (ie making glass objects), is silica in clay to produce a glass. This often hard to identify, but there is nonetheless a happens with clay that is part of a ground signifi cant body of evidence from London c surface, a structure or ceramic. The resulting Fig 57 Large ( 45mm diameter) late Iron Age beads from (Shepherd and Wardle 2009), and from Stanway, near Colchester, Essex. The dark blue glass is glassy material is blue, green or grey, bubbly cobalt-coloured and decoration in different colours has been a number of other urban and military and light weight. It is sometimes called ‘fuel marvered into the surface. settlements (Allen 1998; Price 2002). ash slag’. Fuel ash ‘glazes’ can also be found The commonest fi nds are collections of on stones or ceramic lumps, and these can cullet and working waste, including moils be misidentifi ed as debris from glassworking from blowing, plus vessel and window (see Fig 11). fragments. Crucibles have occasionally been found, more commonly attributed to 7.3 Plastic the later Roman periods (Cool et al 1999). Drops of molten plastic or thin plastic In Roman Britain, glass was used for many fragments can appear superfi cially similar more applications than before. to glass, having a range of colours, varying transparency and a smooth surface. Fig 58 Fragments of Roman glass: a rounded blue cake of 8.3.1 Jewellery, ornaments, counters raw glass and a tessera (10mm cubed), chipped from a cake, However, plastic is less dense than glass from West Clacton, Essex (excavated by CAT). and tesserae and is often pliable or easily dented with Glass featured often in jewellery, as beads, a fi ngernail. It also melts in contact with found in Britain was probably imported bangles and brooch settings, and also something hot, like a heated needle. from the Roman world; it is the same type as enamel on brooches. In Britain, glass (soda-lime-silica natron glass) and contains tesserae were only used very occasionally for 7.4 Geological materials many of the same colourants, opacifi ers or mosaics, and so those found may have been Many naturally occurring materials have decolourisers as glass found at continental traded as a source of coloured glass for other colours, transparency, density and lustre Roman sites. Ultimately a wide range of applications, such as enamelling (Bayley reminiscent of glass, but scientifi c analysis colours came to be used; very dark blue 2005). Glass counters were made for board can distinguish them. Obsidian is a black glass was common. games. Strongly coloured opaque glass was volcanic glass formed naturally – although However, there is some archaeological used for many of these applications, and none occurs in Britain – when lava cools evidence in Britain for glassworking – may have been traded large distances in the rapidly. Crystalline gemstones tend to break shaping and colouring glass – in this period. form of cakes and strips of glass or prepared along cleavage planes and so may have a Finds from probable glassworking sites tesserae (Fig 58). distinctive faceted shape or exhibit a pattern such as Meare Lake Village in Somerset of cracks. Glass tends to produce a fl owing, (Henderson 1987) consist of lumps of 8.3.2 Vessels curved break (called a conchoidal fracture), raw glass, misshapen glass objects and In the Roman period blown vessels (free but was often cut to resemble a gemstone. concentrations of scrap glass and glass blown and mould blown) are found in large artefacts. Although hearths are sometimes quantities for the fi rst time in Britain. Much 8 Chronological Overview found, it is diffi cult to prove their of this was tableware, as well as items for association with glassworking. Also some transportation or storage, such as bottles 8.1 Bronze Age (2500 BC–700 BC) of the yellow, or more rarely white, glass and jars (Price and Cottam 1998). As yet, there is no archaeological evidence from about the 2nd century BC contains Colourless or weakly tinted glass was for the primary production of glass (see colourants (tin-based) that are diff erent very popular, and was used mainly for section 3) during the Bronze Age in from typical Roman glass (Tite et al 2008). tableware. Pale blue-green, naturally Britain, and indications of Bronze Age Glass artefacts from Iron Age Britain coloured glass was most commonly used glass production in Europe are extremely include beads (Fig 57), and the decoration for vessels in the 1st to 3rd centuries AD, rare. In Western Europe, glass artefacts on glass artefacts tends to be more including tableware, bottles and household have been found at sites in Britain, Ireland, elaborate on examples from the later Iron containers. Strongly coloured glass was Switzerland, Italy and Germany (Angelini et Age, for example with blobs or cords of only used for certain types of vessels, such al 2004; Hartmann et al 1997), dating from glass in contrasting colours marvered into as mosaic bowls, particularly in the 1st and as early as the 13th century BC. The glass the surface. In the Late Iron Age there are 2nd centuries, and there is no evidence for is generally transparent blue or turquoise, also some vessels, gaming counters, brooch the production of such vessels in Britain. although rare objects of colourless glass settings and enamels. From the 4th to the 5th centuries AD, an are known, and it was probably made using olive green glass with more noticeable fl aws plant ashes. In Britain, glass was used only 8.3 Roman (AD 43–410) dominates in Roman glass assemblages, for simply formed objects such as beads. Again, there is no conclusive archaeological known as HIMT glass (see Case Study 3). evidence for the primary production of Various decorative techniques were also 8.2 Iron Age (700 BC–43 BC) glass in Roman Britain. The glass was used, including pinched ribs and applied As yet, there is no archaeological evidence probably imported from a small number of decoration, sometimes in strong colours. for the primary production of glass during large-scale production centres elsewhere in Wares were also cut or engraved with the Iron Age in Britain either. Iron Age glass the Roman world (Freestone 2005); it is the bands, facets, scenes or inscriptions.

25 8.3.3 Windows mould blowing, mainly earlier in this Roman window glass is typically c 3mm period. By the end of the early medieval thick and between 0.3 and 0.4m square, period lighter tints again predominated although larger panes are known. It was (Hunter and Heyworth 1999). generally made by casting, resulting in one matt and one glossy surface. The 8.4.3 Windows broad glass method was used from the Small amounts of window glass are found 3rd century onwards (Fig 59) (see section from the end of the 7th century (Cramp 6.3.1), and a small number of small 2000), with increased use in the 9th to 10th (0.2m diameter) circular panes have been Fig 59 Partially melted Roman window glass intended for centuries in churches and cathedrals. There recorded in Britain. recycling, from a glassworking site in London, width 94mm, are documentary sources (Harden 1961) each fragment on average 4mm thick (photo by Andy Chopping/MOLA) that describe workmen being brought from 8.4 Early medieval (AD 410–1066) Gaul to glaze monastery buildings. As before, there is no good evidence of primary glass production in Britain from 8.5 Medieval (AD 1060–1485) this period. Until the 9th to 10th centuries There is, once again, virtually no evidence most of the glass used is similar to earlier for the manufacture of glass in Britain in the Roman glass (soda-lime-silica ‘natron’ 11th and 12th centuries, although greenish glass). Recent research suggests that glass potash window glass has been excavated, for continued to be imported from established example in York. There are historical records sources for some time after the end of the Fig 60 Emerald green and amber 10th- to 11th-century for the Wealden glass industry from the 13th Roman occupation. Subsequently, perhaps lead glass beads from York, c 10mm diameter. to 17th centuries (Godfrey 1975; Kenyon when these trade routes were interrupted, 1967), and for the Staff ordshire industry there was considerable recycling of earlier from the early 14th to the 17th centuries. glass; in some cases the glass may have At this time, the glass was both made and been diluted with other glassy materials shaped using the same furnace, and the (Freestone et al 2008; Henderson 1993). glass was made from the ashes of plants such However, there is evidence for as bracken (Dungworth and Clark 2004; secondary glassworking in post-Roman Jackson et al 2005), together with sand. Britain. Crucibles of probable 6th-century In the Weald, 48 archaeological sites date were found at Buckden, Cambridgeshire, have been identifi ed (Crossley 1994), containing opaque yellow and white two of which have been thoroughly glass (Bayley 2000b). Unusual quantities investigated: mid-14th-century Blunden’s Fig 61 Early medieval linen smoothers from Coppergate, of glassworking waste were found at York, with some weathered potash ‘forest’ glass ones (top Wood and mid-16th-century Knightons Glastonbury Abbey, Somerset, including the right) and some lead slag ones (bottom left) (YAT). (Wood 1965 and 1982). In Staff ordshire remains of furnaces used for glassworking, glass was produced around Bagot’s Park but not glass manufacture, probably by copper and iron respectively (Fig 60). near Abbots Bromley (Crossley 1967; Welch dating from the 7th to 8th centuries AD Linen smoothers, or slick stones, and Linford 2005) and at Wolseley on the and evidence for the production of trail- were used for fi nishing cloth. A few early edge of Cannock Chase (Welch 1997) from decorated, blown vessels (Bayley 2000a). examples were made from a black, lead- the early 14th to the early 17th centuries Evidence of later working, from sites such rich glass now known to be waste slag (see Fig 15), and near Eccleshall from the as Whitby Abbey (Jennings 2005) and from lead smelting (Gratuze et al 2003), late 16th century. The furnaces used, and Barking Abbey, Essex, is less substantial, which was probably imported. Most linen the glass produced, were similar to those consisting of fi nished and waste glass smoothers dating from the 10th century of the Wealden industry. Other glasshouses fragments, small glass blobs and reticella and later are made from dark green or are likely to have existed, although physical rods (MacGowan 1996; Heyworth 1992). brown potash glass (Fig 61); this type of evidence is elusive. Brief documentary ‘forest’ glass became the norm in later references include a glasshouse in Inglewood 8.4.1 Jewellery and linen smoothers centuries (eg Henderson 1993). Forest in Cumbria, and imply glassmaking Glass was used to make beads, often in Colchester and at Salisbury cathedral brightly coloured and opaque (Brugmann 8.4.2 Vessels (Tyson 2000, 8). 2004; Guido 1999; Hirst 2000). Some are Vessels were mainly cups and beakers, tooled, for example, melon beads. Glass such as claw and cone beakers, and, later, 8.5.1 Vessels was also used as an inlay on fi ne metalwork globular beakers and palm cups. Glass The extent of medieval vessel manufacture (Bimson and Freestone 2000). in green and blue shades dominates; in Britain is unclear. Excavations have Evidence for the working of high-lead although some nearly colourless glass was revealed a few fragments of green potash glass – including crucibles, lumps of cullet used earlier in this period and a larger glass vessels such as fl asks, hanging lamps and objects – has been found from the 10th proportion of slightly later vessels are and urinals at the same glasshouses that century onwards (see section 2.1), but little in strong hues of blue or green to black made window glass. These were generally evidence of manufacture of this glass from (Evison 2008). Vessels were decorated undecorated, although some fl asks had raw materials has yet been identifi ed in using prunts and trails or blobs of applied optic-blown ribbing. It is possible that Britain. This type of lead glass was used glass that were pulled downwards to make slightly more decorative fl asks or jugs, to make rings and beads, and is generally the characteristic decoration seen on claw and beakers were made on these sites. translucent amber or green to black, coloured beakers. Ribbed vessels were made using Documentary references imply that distilling

26 vessels were also made at English furnaces. in the mid-19th century, regenerative 8.6.3 Windows More decorative glass tablewares were furnaces, which used gas, but the glass was Various types of glass of diff ering used on high-status sites in Britain in this still held in pots. Continuous tank furnaces appearance were used to make window period, but they were imported mainly from were used in Britain from the 1870s. glass (Fig 62) – for details see Case Study 2. Europe, and even included a few vessels From 1745 taxation based on the from the Islamic eastern Mediterranean 8.6.1 Fine vessels weight of glass rather than on the window (Tyson 2000). Imported vessels were made Early post-medieval vessel glass is described area favoured crown glass, which was in potash glass from Europe, soda glass from by Willmott (2002). Fine drinking glasses thinner, so broad glass production went Europe and the eastern Mediterranean, were made from virtually colourless glass. into decline in Britain until the mid-19th with a smaller number of yellow, bright Examples include the renowned ‘cristallo’ century, and crown glass dominated. green and opaque red high-lead glass (crystal glass), imported from Venice, which However, broad glass was used for tablewares produced in the 13th and early was made using the purifi ed ashes from some applications, for example for coach 14th centuries in Germany. specially selected plants. Colourless alkali windows and mirrors, where large panes glass in the Venetian style (crystal or ‘Façon of fl at glass with an excellent surface fi nish 8.5.2 Windows de Venise’) was also produced by immigrant were required. These expensive sheets of The major products of both the Wealden Italian glassmakers based in London glass were made thicker than usual and and Staff ordshire industries were plain (Godfrey 1975, 17). Similar glass continued then polished (blown plate) (see section colourless (‘white’) window glass. to be made throughout the 17th century, 6.3.1) (Louw 1991). From the later 18th Documentary sources list specifi c orders, even after the development of colourless century larger panes were made in Britain for example from the Weald for the royal lead glass in the 1670s, which was also used by polishing cast sheets of glass (cast plate); chapels of St Stephen’s, Westminster, and for fi ne vessels (Charleston 1984, 97). in the previous century it had been imported for St George’s Windsor. Excavated fragments The production of colourless lead from France (see sections 6.3.4 and 6.4.3). show that window glass was made using glass was famously patented by George In the 1830s, ‘patent plate’ was developed, either the crown or broad glass methods. Ravenscroft in 1674 (Dungworth and Brain in which thinly blown cylinder glass could 2009). Lead glass was initially made using be polished. Cylinder window glass grew 8.6 Post-medieval (AD 1485–present) fl int as a source of low-impurity silica. in popularity in the 19th century. From the There were dramatic changes to the English Lead glass, also known as lead crystal or early 20th century, sheet glass was drawn glass industry in the late 16th century ‘fl int glass’, even when white sand was from continuous tank furnaces (Krupa and following the arrival of glassmakers from used instead, was quickly adopted by other Heawood 2002) (see section 6.3.5). continental Europe (Godfrey 1975). One English glassmakers (Dungworth and of these glassmakers, Jean Carré, obtained Cromwell 2006) and helped establish Britain 8.6.4 Specialised glass monopoly rights to glass production in as a leading glass manufacturing nation. The In the 19th and 20th centuries the market England and Ireland in 1567. He established import of Venetian and Venetian style vessels for specialised glass became increasingly a glasshouse in London for making virtually ceased (Crossley 2003). important to glassmakers in Britain. In the colourless soda-lime-silica plant ash ‘crystal’ 19th century, lenses for lighthouses and glass and a number of other glasshouses in 8.6.2 Bottles observatory telescopes were developed with the Weald (Kenyon 1967) making greenish The earliest post-medieval bottles were technical expertise obtained from French lime-rich (HLLA) glass from the ashes made from greenish HLLA glass, and were glassworkers. New types of glass with of hardwood species like oak and beech. generally small and thin-walled. From the particular properties were formulated, such Other immigrant glassworkers followed, mid-17th century the dark green, thick- as borosilicate glass, which had increased established glasshouses elsewhere, walled ‘English bottle’ made its appearance. durability, and resistance to chemicals and including Wiltshire, Gloucestershire (Vince Bottlemakers were unconcerned about heat, and glass that would protect against 1977), Herefordshire (Bridgewater 1963), impurities in their raw materials, as they UV radiation. Glass was used for syringes, Shropshire (Pape 1934), and Yorkshire did not want a colourless glass. Excise rules microscope slides, camera lenses, tubing (Crossley and Aberg 1972). The traditional introduced in 1745 only allowed them to and reagent bottles. In the 20th century, potash glass of previous centuries was use the cheapest ingredients, but these glass began to be used in cathode ray tubes, abandoned (Dungworth and Clark 2004). restrictions were removed in 1845 and initially for radar systems (see Fig 46). Initially, the furnaces from this period some bottles were then made in colourless are similar to earlier ones – see section 5.1 soda-lime-silica glass (Wills 1974, 52). for details. When wood fuel was banned for The earliest post-medieval bottles glassworking in England in the early 17th were free-blown (Van den Bossche 2001). century, the last of the Wealden glasshouses Mould-blown cylindrical bottles became closed down by 1619. Instead glasshouses increasingly popular from the mid-17th were established in areas with easy access century. Piece moulds, which enabled letters to coal, in particular Newcastle (Godfrey and designs to be embossed on the exterior 1975), Stourbridge (Guttery 1956), Bristol of the bottle, were developed in the 19th (Witt et al 1984) and Yorkshire (Ashurst century (Wills 1974). At the beginning of the 1992; Crossley 2003). Glass furnace design 20th century fully automatic bottle-making also changed slightly to accommodate coal machines could both gather the glass and fi ring (see Fig 13). blow it into suitable moulds (Cable 2002). In the late 17th to early 18th centuries Soda-lime-silica glass performed better in Fig 62 The characteristic colours of post-medieval window cone-shaped cover buildings were developed these machines, so HLLA glass was fi nally glass, from green (HLLA), to pale blue (kelp) to colourless (see Figs 20 and 21; and section 5.1), and abandoned (see section 6.2.2). (synthetic soda).

27 9 Summary table

Bronze Age 2500 BC–700 BC Iron Age 700 BC–AD 43 Roman AD 43–AD 410

Glass type Mixed-alkali or soda-lime silica Soda-lime-silica ‘natron’ glass. 1 Mainly soda-lime-silica ‘natron’ glass. plant ash glass. 2 Plant ash component in some strongly coloured glass (red and green).

Raw materials Alkali -rich ashes of halophytic Natron and sand. Sand with: plants and sand. 1 Natron. 2 Rarely, with plant ashes.

Glass Unknown, possibly imported. Unknown, probably imported. No conclusive evidence of manufacture yet known manufacture from Britain (primary 1 Natron glass probably imported 2 production) Made in large tank furnaces at a small number of sites and transported as chunks of raw glass 3 Coloured glass traded in form of cakes, strips or tesserae.

Glass shaping No evidence of glassworking Rare evidence in Britain. Substantial evidence of glassworking in Britain, (secondary in Britain. including moils (from glassblowing), scraps of production) Includes malformed beads, chunks of glass, vessels, glass fragments, trails and dribbles. scrap glass and moulds. Furnace remains rare – small tank furnaces and pot furnaces c 1m diameter.

Crucibles often contemporary pottery types about 100mm diameter.

Glassworking Shaping. Shaping, core forming, applied glass decoration Shaping, blowing, mould-blowing, optic blowing, methods (trails, etc). casting or slumping over moulds, wheel-cutting, engraving, applied glass decoration (trails, etc).

Colours Mainly transparent turquoise Dominated by dark blue (cobalt oxide) and also Mainly colourless glass or glass with a blue-green (copper oxide). red (cuprous oxide); other colours were purple tint (decolourised with manganese oxide or (manganese oxide), yellow and white (the antimony oxide). Some strongly coloured, often tin-based colourants lead stannate and tin opaque, glass in the 1st to 2nd centuries includes oxide respectively). These were later replaced dark blue, red, yellow and white (as before), by the antimony-based colourants: yellow lead turquoise (copper oxide), green (iron oxide, antimonate and white calcium antimonate. copper oxide or a mixture of yellow and blue colourants), brown (iron and sulphur) and purple (manganese oxide).

Artefacts Beads Jewellery (beads). Jewellery (beads, bangles, brooch enamels and Later: vessels, brooch settings and gaming settings), gaming counters. counters. Tableware (cups, beakers and bowls), flasks, prismatic bottles, unguent bottles. Windows, tesserae.

Research Artefacts and evidence of Artefacts and evidence of glassworking rare; Glassworking evidence fairly rare. status glassworking very rare. All aspects would existing typologies for beads; technological Existing typologies for artefacts. benefit from study. studies of red enamel. Some comprehensive studies of glassworking Potential for further study of glass sources, waste, particularly in London, plus technology and technology, trade and use; possibility of refining source. Potential for further study of particular date. topics such as use of glass, industry organisation, trade and furnace technology.

28 Early medieval AD 410–AD 1066 Medieval AD 1066–AD 1485 Post-medieval AD 1485–Present

1 Soda-lime-silica ‘natron’ glass. 1 Mainly potash-rich plant ash glass (‘forest’ glass). As medieval, then from late 16th century: Rarely, from the 10th century: 2 Some soda-lime-silica glass (mostly ‘natron’ glass, 1 HLLA (high-lime low-alkali) plant ash glass. 2 Potash-rich plant ash glass (‘forest’ glass). rarely plant ash glass). 2 Soda-lime-silica or mixed alkali plant ash glass 3 Lead glass. 3 Rarely, lead glass. (‘Façon de Venise’, ‘crystal’ or ‘white’ glass). 4 Black lead slag. 3 Lead crystal or flint glass. 4 In the 18th and 19th centuries:mixed-alkali kelp glass. 5 From c 1830 soda-lime-silica synthetic soda glass.

Sand with: Sand with: Sand (or ground flint) with: 1 Natron. 1 Potassium-rich plant ash, such as from bracken. 1 Plant ashes from woody species, such as beech or oak. 2 Plant ash, such as from bracken. 2 Mainly natron or rarely sodium-rich plant ashes. 2 Purified alkali-rich plant ashes. 3 Lead oxide. 3 Lead oxide. 3 Lead oxide and potassium salts (saltpetre). or 4 Kelp (seaweed ash). 4 Lead smelting slag. 5 Synthetic soda (sodium carbonate made from salt cake). Sometimes other materials also, eg borax, barytes, soap boilers waste and blast furnace slag.

No evidence yet from Britain. 1 Some potash-rich plant ash glass imported, but Glass manufacturing concentrated in the Weald and 1 Natron glass probably made in large tank evidence of manufacture in Britain from 13th Staffordshire, as before, then: furnaces and imported but recycling also. or 14th century onwards, focused in Weald and 1 From mid-16th century: also London. 2 Origins of plant ash glass unknown. Staffordshire. 2 From early 17th century: change to coal fuel, industry 3 Origins of lead glass unknown. 2 Natron glass probably imported. spreads to Gloucestershire, Lancashire, 4 Black lead slag probably imported. 3 Lead glass may originate in Germany. Nottinghamshire, Staffordshire, Tyneside, Worcestershire and Yorkshire.

Some evidence of glassworking in Britain. Glassworking at primary production sites (see above). Glassworking at primary production sites (see above); furnaces as medieval, then: Furnaces roundish in plan, c 1m diameter. Furnaces rectangular, 3m by 4m to 5m, with parallel 1 From mid-16th century: more refractory bricks used. sieges. 2 From early 17th century: below-ground fire trench Crucibles sometimes contemporary pottery or flue. types c 100mm diameter. Crucibles custom-made, sandy fabric, c 0.3m tall. 3 From late 17th or early 18th century: cones over furnace from 18m high; extensive subterranean flues; many large associated structures (eg annealing sheds, workshops); crucibles custom-made from grogged, refractory clays; 19th-century crucibles c 1.4m deep; closed crucibles used for ‘lead crystal’ or ‘flint’ glass.

Shaping, blowing, optic blowing, mould blowing, Shaping, blowing, optic blowing, mould blowing, Shaping, blowing, casting, engraving, mould blowing, applied glass decoration (trails, prunts, reticella, etc). applied glass decoration, painting, flashing. optic blowing, mechanised mould blowing, applied glass decoration, cutting, grinding and polishing, automated grinding and polishing, pressing, painting, flashing, enamelling.

Mainly shades of blue or green. Some colourless 1 Potash-rich plant ash glass – green. 1 Plant ash HLLA glass – green. and brown earlier vessels; more strongly coloured 2 Soda-lime-silica ‘natron’ glass – colourless and 2 Soda-lime-silica or mixed alkali ‘Façon de Venise’, ‘crystal’ vessels later. coloured (colourants as early medieval). or ‘white’ glass – colourless. Colourants as Roman except return to lead 3 Lead glass – mainly yellow, some green or red. 3 Lead crystal or flint glass – colourless. stannate for yellow glass and tin oxide for white. 4 Kelp glass – very pale blue-green. 5 Soda-lime-silica synthetic soda glass – colourless. Colourants as before with range increasing over time to include eg uranium, nickel, chromium and gold; bone ash (calcium phosphate) for opalescent glass; arsenic trioxide for decolourising/refining.

Jewellery (beads, rings), linen smoothers. Jewellery (beads, gems). Jewellery. Vessels (cups, beakers, horns, flasks). Vessels (beakers, goblets, bowls, flasks, jugs, bottles). Vessels. Windows. Windows, mirrors. Windows, mirrors. Lamps, lenses. Lamps, lenses. Distilling apparatus, uroscopy flasks. Scientific apparatus.

Artefacts and evidence of glass working rare. Artefacts rare. Glassworking evidence regionally localised: generally rare. Potential to refine typologies. Glassworking evidence regionally localised: Potential for further study: There is evidence of different glass types being generally rare. 1 To clarify the distribution of the industry, the type of fuel used, but further study required to establish glass Potential to refine typologies. used and the type of glass produced sources, technologies, trade and use, and industry Potential for further study of: 2 Of resources consumption and management organisation. 1 Trade and use of English and imported glass. 3 Of technical innovations (often implemented secretly) 2 Industry resource consumption and landscape 4 Of specialisation, for example industrial glass, management. photographic glass, optical glass, architectural glass, 3 Influences on glass deterioration. scientific equipment and so on.

29 10 Where to go for help Advisors are based in the regional offi ces periods; organise meetings and publish a and are available to provide independent, newsletter 10.1 Further reading non-commercial advice on all aspects of Prehistoric and Roman beads are described archaeological science. For contact details Corpus Vitrearum Medii Aevi by Guido (1978) and compositional data visit the English Heritage website at http:// http://cvma.ac.uk are provided in papers by Henderson. www.english-heritage.org.uk/, select the A resource for medieval stained glass in Shepherd and Wardle (2009) provide ‘Professionals’ tab, then the ‘Advice’ menu, England, including a digital archive of a well-illustrated summary of the Roman ‘Advice by Topic’ and fi nally ‘Heritage painted and stained window glass, plus glassworking waste found in London. The Science’. conservation guidelines various Roman vessel forms and colours The English Heritage Archaeological are described by Price and Cottam (1998). Conservation and Technology team, based Institute of Conservation Compositional data for Roman glass from at Fort Cumberland in Portsmouth, can http://www.icon.org.uk/ Britain from the 1st to 3rd centuries AD are advise on the identifi cation, scientifi c ICON represents those concerned with the discussed in papers by Jackson (2005). The analysis, interpretation and conservation of conservation of cultural heritage in the UK. results and implications of scientifi c analyses archaeological remains from glassworking. The site includes the Conservation Register of glass are discussed by Freestone and They can also provide contact details for of accredited conservators / restorers and a co-authors, and summarised by Freestone individuals and institutions undertaking range of guidance material. (2005). commercial investigations and analysis of Evison (2008) covers the diff erent glassworking assemblages. Institute for Archaeologists forms of early Anglo Saxon glass, and the E-mail: david.dungworth@english- http://www.archaeologists.net/ appendix by Freestone et al (2008) gives an heritage.org.uk; or for conservation advice For general information, including up to date summary of scientifi c discoveries e-mail [email protected]. standards, on the practice of archaeology on this subject. For further information uk, tel: 02392 856700 and allied disciplines on glass from the later end of this period, Most scientifi c analysis of glass takes including compositional data, see Hunter place within the archaeological science or Roman Glass Research Project and Heyworth (1999). Whitehouse (2010) archaeology departments of universities, http://www.mymuseumofl ondon.org.uk/ includes colour images of vessels, plus for example Bournemouth, Bristol, blogs/romanglass/ contemporary artwork showing vessels in use. Cardiff , Cranfi eld, Nottingham, Sheffi eld, An informative account of the recording Tyson (2000) describes glass vessel Royal Holloway University of London and and interpretation of the large Roman forms from 1200 to 1500. The medieval University College London, plus the British glassworking assemblage from Basinghall, Wealden glass industry is discussed in great Geological Survey in Nottingham. The London, by Angela Wardle of Museum of detail by Kenyon (1967) and reviewed by material may be used for student projects. London Archaeology (MOLA), including Crossley (1994), with detailed examples Some information is available through photographs published by Wood (1965 and 1982). The the websites for these organisations. 1997 article by Welch on Wolseley and the The English Heritage Archaeological Roman Glassmakers 1967 article by Crossley on Bagot’s Park Conservation and Technology team http://www.romanglassmakers.co.uk/ provide comprehensive descriptions of the can provide contact details for other A website focusing on the glassworking late medieval industry in Staff ordshire. practitioners. methods used to make diff erent types of The post-medieval glass industry is Currently there is no one source for Roman vessel, including information on concisely summarised in Crossley’s Post- fi nding active glass specialists. However, the experimental Roman furnace projects. Medieval Archaeology in Britain (1990) contact details of consultants are available Now also working on 13th to 17th century and in Crossley (2003). Willmott (2002) from the IFA and from AHG, and from glassworking techniques. summarises glassmaking 1500–1670 and the English Heritage Archaeological classifi es glass vessels found in England. Conservation and Technology team (see The British Society of Master Glass Examples of the application of sampling details above). Painters strategies and scientifi c analysis to English The Conservation Register of the http://www.bsmgp.org.uk/ glassworking waste feature in Dungworth Institute of Conservation (ICON) is a A website exclusively for historic and and Cromwell (2006), Dungworth and register of privately practising conservators contemporary stained glass. Resources Paynter (2006) and also Bayley et al and conservation laboratories that are include a journal, newsletter and reference (2008). Brill (1999) contains a vast accredited by ICON and are required to library. compilation of compositional data on glass work to professional standards set out from many locations and periods. by ICON. The register is free to use and The Corning Museum of Glass, New York For information on treatises and records it is possible to search for a conservator http://www.cmog.org/ about glass, see Hoover and Hoover (1950) by location and specialism: www. Information and images for ancient through and Cable (2001). Examples of the use of conservationregister.com, e-mail: info@ to contemporary glass in the museum other types of documentary evidence are conservationregister.org.uk collection; the site has on-line demonstrations included by Crossley (1972), Dungworth of glassworking techniques for glass of all and Paynter (2006) and Godfrey (1975) in 10.3 Useful organisations periods under ‘Glass Resources’, then ‘Videos’ their discussions of the medieval and post- and ‘Glassworking video clips’. medieval glass industry. Association for the History of Glass http://www.historyofglass.org.uk/ The Glass Association 10.2 Specialist advice All aspects of glass, with strengths in http://www.glassassociation.org.uk/ The English Heritage Regional Science archaeology and archaeometry of all Based at the Broadfi eld House Glass

30 Museum, with strengths in post-medieval cone a conical chimney covering the but the inside is pale and opaque and contemporary glass and glassmaking working area and furnace from the late because it contains numerous quartz 17th / early 18th centuries (see section grains. Faience predates glass and was The Glass Circle 5.1) commonly used for beads. http://www.glasscircle.org/ cristallo colourless, high quality glass fl ashing a thin layer of coloured glass An emphasis on glass collections, with lists imported from Venice, which was made applied to the surface of colourless glass of dealers, auction houses and museums. using purifi ed plant ashes (see section (see section 6.4) Publishes the newsletter Glass Circle News. 8.6) fl int glass originally the name given to crown a disc of window glass made post-medieval lead glass made with fl int The Guild of Glass Engravers by blowing a gather of glass, then pebbles as the source of silica, but later http://www.gge.org.uk/ transferring this to a pontil iron and a general term used for all lead crystal A professional body for glass engravers spinning it until it opened up (see section glass (see sections 2.1 and 8.6) with descriptions and examples of diff erent 6.3) fl oat glass from the mid-20th century, engraving techniques crucible the ceramic container used to hold a method for making sheet glass of the melted glass in pot furnaces (see also uniform thickness with smooth surfaces The Society of Glass Technology pot and section 5.4) by fl oating glass on a bed of molten tin http://www.sgt.org crizzling a network of fi ne cracks that forest glass a greenish coloured, potash- A resource for all aspects of glass, but forms in unstable glass, particularly rich glass made from plant ashes, strengths in scientifi c studies and post- post-medieval lead glass (see Fig 4) common in the medieval period and medieval glass; organise meetings and cullet glass collected for recycling, which prone to weathering (see section 2.1) publish a journal is likely to be a mixture of glass made at fritting the process of roasting the glass the site and glass made elsewhere (see batch prior to melting Vidimus section 3.3) gather a mass of glass collected on a http://www.vidimus.org/ cylinder glass see broad glass blowing iron or punty, for subsequent Free access to a monthly on-line magazine decolouriser compounds such as antimony working on medieval stained glass or manganese oxides, which were added glass a non-crystalline solid to glass to make it appear colourless by HIMT glass a type of soda-lime-silica counteracting the colour produced by ‘natron’ glass, characterised by high iron, 11 Glossary impurities in the raw materials, such as manganese and titanium (HIMT) levels. iron oxide It is common from the 4th century AD annealing the process of gradually cooling dichroic glass that appears one colour and is olive green, often with bubbles worked glass, which would otherwise in refl ected light and another in and fl aws (see Case Study 3). shatter if cooled quickly transmitted light HLLA glass a green-coloured, high-lime annealing oven the structure in which drawing refers to mechanised methods of low-alkali glass, common from the annealing took place (see also lehr, extracting a cylinder or, more commonly, second half of the 16th century, made annealing and sections 3.6 and 5.2) a sheet of glass from a melt. Sheets from plant ashes (see section 2.1) barilla a term for the ashes of halophytic were drawn from tank furnaces using inlay a solid piece of material set into, (salt tolerant) plants, which provided a equipment that gripped a layer of glass and usually level with, the surface of fairly pure source of sodium oxide fl ux. as it started to solidify. an object Prized for making high quality glass Egyptian blue This pigment predates glass kelp is a term for a type of seaweed, and (see section 3.1), large amounts were and is a striking bright blue. In Britain also ash from burning the seaweed, imported from Spain in the 18th and it is more common from Roman sites. which was used as a source of sodium 19th centuries It is made from crushed quartz or sand, oxide fl ux in glassmaking in the 18th batch the raw materials for making glass mixed with alkali fl uxes and a copper and early 19th centuries (see sections 8.6 blowing iron a long iron tube that was colourant, which is then fi red. It is not and 3.1 and Case Study 2) dipped into the molten glass to collect completely glassy and contains many lehr or leer a structure used for annealing. a gather for subsequent infl ating and cuprorivaite crystals that cause the From the 19th century these were shaping (see section 6.2) colour. constructed as tunnels, heated at one broad glass window glass made by blowing enamel coloured glass fused onto the end. The glass passed slowly through a gather of glass, elongating it into a surface of another material, such as the lehr on a system of carriers (see also cylinder, removing the ends, slitting the metal, glass or glazed pottery annealing oven and sections 3.6 glass tube along its length and opening eye the hole in the centre of the furnace and 5.2). it up (see section 6.3) fl oor in coal-fi red furnaces through marver a fl at surface, of stone or metal, on cane a multicoloured glass rod, made by which the fl ames and heat entered (see which the glassworker rolls or presses heating, perhaps twisting and extending section 5.1) the glass to help shape it (see section 6.4) together a number of individual rods of Façon de Venise colourless alkali glass in marvered decoration glass decoration, diff erent colours the Venetian style, also referred to as such as trails or blobs in diff erent cast plate a method introduced in the 18th crystal glass, produced from the mid- colours, that are fl ush with the surface of century to make large sheets of fl at glass 16th century (see section 8.6) the glass. The decoration is pushed into with a good surface fi nish. Molten glass faience made by shaping a moist paste the glass while hot using the surface of was cast onto a metal table and rolled of crushed quartz or sand, mixed with the marver. into a fl at sheet, then polished fl uxes and a colourant, followed by metal a term sometimes used for molten (see section 6.3). fi ring. Faience has a glassy surface, glass

31 mixed-alkali glass glass containing rod end cullet sometimes used for Ashurst, D 1992 The History of South signifi cant amounts of both the alkali describing glass moils that were directly Yorkshire Glass. Sheffi eld: Collis fl uxes sodium oxide (Na2O) and in contact with the blowing iron during potassium oxide (K2O) glass blowing, and were later recycled. Bayley, J 2000a ‘Saxon glass working at moil the leftover top of a blown object Some have oxidised iron scale attached. Glastonbury Abbey’, in Price, J (ed) Glass in where it was joined to the blowing iron, More commonly referred to as moils Britain and Ireland AD350–1100. Brit Mus generally in the form of a cylindrical (see above). Occas Pap 127. London: Brit Mus P, 161–88 collar or tube of glass. This waste is saltcake a high purity, synthetic sodium diagnostic of glass blowing (see section sulphate made from sea salt, used in Bayley, J 2000b ‘Glassworking in early 6.2) and is sometimes referred to as rod glass production from the 1930s medieval England’, in Price, J (ed) Glass in end cullet (see below). saltpetre potassium nitrate, a potassium- Britain and Ireland AD 350–1100. Brit Mus natron sodium-rich salts formed by rich fl ux used in the production of post- Occas Pap 127. London: Brit Mus P, 137–42 evaporation at mineral-rich lakes, for medieval lead glass (see section 3.1) example at the Wadi Natrun in Egypt. siege the two low, parallel platforms in Bayley, J 2005 ‘Roman enamel and Natron was the alkali fl ux used to make medieval and post-medieval furnaces enamelling: new fi nds from Castleford, late Iron Age, Roman and early medieval on which the crucibles of glass sat (see Yorkshire’. Annales du 16e Congrès de glass (see section 3.1). section 5.1) l’Association Internationale pour l’Histoire obsidian is a black, volcanic glass that soda ash sodium carbonate, an alkali fl ux du Verre London 2003. Nottingham: AIHV, occurs naturally, although not in Britain (see section 3.1) 72–4 opacifi er small particles of a substance in a soda-lime-glass includes ‘soda-ash’ and glass that scatter light, making the glass ‘natron’ glass. Soda-lime-glass is typical Bayley, J and Doonan, R 1999 ‘High-lead opaque of the Iron Age, Roman and much of the glassworking and alkali glass bead making optic blowing A gather of glass is blown early medieval periods, and also from at 16–22 Coppergate and 22 Piccadilly, into a mould with a pattern on the around the 19th century (see section York’. Ancient Mon Lab Rep 74/1999. inner surface, which transfers to the 2.1) London: English Heritage glass. Continued free blowing results in tank furnace a furnace in which the movement and distortion of the pattern molten glass is held in an integral tank, Bayley, J, Dungworth, D and Paynter, (see section 6.2). rather than pots. In Britain, small tank S 2001 Archaeometallurgy. Centre for overblow a by-product of mould blowing, furnaces may have been used in the Archaeology Guidelines 2001/01. referring to the glass that remains Roman period. Large tank furnaces were Swindon: English Heritage outside the mould, which is removed introduced in the late 19th century (see and recycled section 5.1). Bayley, J Dungworth, D and Paynter, S paraison the partially infl ated gather of uroscopy diagnosing medical conditions by 2008 ‘Science for historic industries – glass at the end of the blowing iron the visual examination of urine glass and glassworking’, in Horning, A paraison end a marble-shaped blob of weathering physical and chemical J and Palmer, M (eds) Crossing Paths or glass pinched from the end of the gather alteration of glass, particularly the Sharing Tracks? Future Directions in the during the blowing of particular forms, surface, varying with the type of glass Archaeological Study of Post-1550 Britain such as the bowls of goblets (see section and the environmental conditions and Ireland. Woodbridge, Suff olk: Boydell 6.2 and Fig 43) and Brewer Ltd, 117–32 pontil or punty a solid iron rod onto which a blown article is transferred for further References Bimson, M and Freestone, I C 2000 hot working (see section 6.2) ‘Analysis of some glass from Anglo-Saxon pontil scar the circular protrusion of glass ACAO (Association of County jewellery’, in Price, J (ed) Glass in Britain left on a glass object after removal of the Archaeological Offi cers) 1993 Model and Ireland, AD 350–1100. Brit Mus Occas pontil iron, although it was ground away Briefs and Specifi cations for Archaeological Pap 127. London: Brit Mus P, 131–6 on fi ner vessels Assessments and Field Evaluations. pot see crucible Haddington: Connolly Bowman, S 1990 Radiocarbon Dating. pot furnace In furnaces from the Roman London: British Museum period onwards, the glass was held in Allen, D 1998 Roman Glass in Britain. ceramic pots or crucibles (see section 5.1) Princes Risborough: Shire Publications Bridgewater, N P 1963 ‘Glasshouse Farm, St potash potassium carbonate, an alkali fl ux Weonards: a small glassworking site’. Trans used in glassmaking, obtained from Angelini, I, Artioli , G Bellintanib, P, Woolhope Naturalists’ Field Club 37, 300–15 plant ashes Diellac,V, Gemmia, M, Polla, A and Rossi, potash glass potassium-rich glass, made A 2004 ‘Chemical analyses of Bronze Age Brill, R 1999 Chemical Analyses of Early from plant ashes and dominating from glasses from Frattesina di Rovigo, Northern Glasses. Vol. 1, The Catalogue and Vol. 2, The the 10th to the late 16th century (see Italy’. J Archaeol Sci 31, 1175–84 Tables. Corning, NY: The Corning Museum sections 2.1 and 8.5) of Glass prunt decoration in the form of cone- Ashmore, P 1999 ‘Radiocarbon dating: shaped protrusions of applied glass, for avoiding errors by avoiding mixed samples’. Brugmann, B 2004 Glass Beads from example on early medieval vessels (see Antiquity 73, 124–30 Early Anglo-Saxon Graves: a Study of the sections 6.4 and 8.4) Provenance and Chronology of Glass Beads quarry a diamond or square shaped pane of Ashurst, D 1970 ‘Excavations at Gawber from Early Anglo-Saxon Graves, Based on glass cut for glazing windows glass house’. J Post-Med Archaeol 4, 92–140 Visual Examination. Oxford: Oxbow.

32 Cable, M (ed) 2001 The World’s Most Dungworth, D B and Clark, C 2004 ‘SEM- Gould, S 2008 Understanding Historic Famous Book on Glassmaking. The Art EDS analysis of Wealden glass’. Centre Buildings: policy and guidance for local of Glass, by Antonio Neri, Translated into Archaeol Rep 54/2004. Portsmouth: planning authorities. Swindon: English English by Christopher Merrett. Sheffi eld: English Heritage Heritage Society of Glass Technology Dungworth, D and Cromwell, T 2006 ‘Glass Gratuze, B, Foy, D, Lancelot, J and Cable, M 2002 ‘The mechanisation of glass and pottery production at Silkstone, South Tereygeol, F 2003 ‘Les “lissoirs” container production’. Trans Newcomen Soc Yorkshire’. J Post-Med Archaeol 40, 160–90 carolingiens en verre au plomb: mise en 73, 1–31 évidence de la valorisation des scories Dungworth, D and Paynter, S 2006 Science issues du traitment des galènes argentifères Cable, M 2004 ‘The development of fl at for Historic Industries. Guidelines for the de Melle (Deux Sevres)’, in Foy, D and glass manufacturing processes’. Trans Investigation of 17th- to 19th-century Nenna, M-D (eds) Echanges et Commerce Newcomen Soc 74, 19–43 Industries. Swindon: English Heritage du Verre dans le Monde Antique. Monogr Instrumentum 21. Montagnac: Monique Cable 2008 Bontemps on Glass Making. English Heritage 2008 Investigative Mergoil, 101–7 The Guide du Verrier of Georges Bontemps. Conservation. Guidelines on how the detailed Sheffi eld: The Society of Glass Technology examination of artefacts from archaeological Guido, M 1978 The Glass Beads of the sites can shed light on their manufacture and Prehistoric and Roman Periods in Britain and Charleston, R 1984 English Glass and the use. Swindon: English Heritage Ireland. Woodbridge: Soc Antiq London Glass Used in England, c 400–1940. London: Allen and Unwin English Heritage 2010 PPS5 Planning for the Guido, M 1999 The Glass Beads of Anglo- Historic Environment: Historic Environment Saxon England c AD 400–700: A Preliminary Planning Practice Guide. Swindon: English Cool, H E M, Jackson, C M and Monaghan, Visual Classifi cation of the More Defi nitive and Heritage J 1999 ‘Glass-making and the Sixth Legion Diagnostic Types. Rep Res Comm Soc Antiq at York’. Britannia 30, 147–61 London 58. Woodbridge: Soc Antiq London English Heritage 2011 Environmental Archaeology: a guide to the theory and Cramp, R 2000 ‘Anglo-Saxon window glass’, Guttery, D R 1956 From Broad-Glass to Cut practice of methods, from sampling and in Price, J (ed) Glass in Britain and Ireland Crystal. London: Leonard Hill recovery to post excavation. Centre Archaeol AD 350–1100. Brit Mus Occas Pap 127. Guidelines. Swindon: English Heritage London: Brit Mus P, 105–14 Harden, D B 1961 ‘Domestic window glass, Roman, Saxon and medieval’, in Jope, E M Evison, V 2008 Catalogue of Anglo-Saxon Crossley, D W 1967 ‘Glassmaking in (ed) Studies in Building History. London: Glass in the British Museum. Brit Mus Res Bagot’s Park, Staff ordshire, in the sixteenth Oldhams, 39–63 Publ 167. London: Brit Mus P century’. J Post-Med Archaeol 1, 44–83 Hartmann , G, Kappel, I, Grote, K and Foy, D and Nenna, M-D 2001 Tout Feu Tout Crossley, D W 1972 ‘The performance of Sable. Musées de Marseille: Éditions Édisud Arndt, B 1997 ‘Chemistry and technology the glass industry in sixteenth-century Free stone, I C 2005 ‘The provenance of prehistoric glass from Lower Saxony and England’. Econ Hist Rev 25, 421–33 of ancient glass through compositional Hesse’. J Archaeol Sci 24, 547–59 analysis’, in Vandiver, P B, Mass, J L and Crossley, D 1990 Post-Medieval Archaeology Murray, L A (eds) Materials Issues in Art Hawthorne, J G and Stanley Smith, C (eds) in Britain. Leicester: Leicester U P and Archaeology, Vol 7. Warrendale, PA: 1979 Theophilus: On Divers Arts. New York: Materials Res Soc, Chapter 8.1 Dover Crossley, D W 1994 ‘The Wealden glass industry re-visited’. Indust Archaeol Rev 17, Freestone, I C 2008 ‘Pliny on Roman Henderson, J 1987 ‘The archaeology and 64–74 glassmaking’, in Martinón-Torres, M and technology of glass from Meare Village Rehren, Th (eds) Archaeology, History and East’, in Coles, J M Meare Village East. The Crossley, D W 2003 ‘The archaeology of Science: Integrating Approaches to Ancient excavations of Arthur Bulleid and H St George the coal-fuelled glass industry in Britain’. Materials. London: UCL InstArchaeol Publ, Gray 1932–1956. Somerset Levels Pap 14. Archaeol J 160, 160–99 77–100 Exeter: Somerset Levels Project, 170–82

Crossley, D W and Aberg, F A 1972 Freestone, I Hughes, M J Stapleton, C P 2008 Henderson, J 1991 ‘Industrial specialization ‘Sixteenth-century glass-making in ‘The composition and production of Anglo- in late Iron Age Britain and Europe’. Yorkshire: excavations at furnaces at Saxon glass’, in Evison, V Catalogue of Anglo- Archaeol J 148, 104–48 Hutton and Rosedale, North Riding, 1968– Saxon Glass in the British Museum. Brit Mus 1971’. J Post-Med Archaeol 6, 136–41 Res Publ 167. London: Brit Mus P, 29–46 Henderson, J 1993 ‘Aspects of early medieval glass production in Britain’. Dreiser, P and Matcham, J 2006 The Gillispie, C C (ed) 1959 A Diderot Pictorial Annales du 12e Congrès de l’Association Techniques of Glass Engraving. London: A Encyclopedia of Trades and Industry. New Internationale pour l’Histoire du Verre. and C Black York: Dover Amsterdam: AIHV, 247–59

Dungworth, D and Brain, C 2009 ‘Late Godfrey, E S 1975 The Development of Heyworth, M 1992 ‘Evidence for early 17th-century crystal glass: an analytical English Glassmaking, 1560–1640. Chapel medieval glass production in north-west investigation’. J Glass Stud 51, 111–37 Hill, NC: U North Carolina P Europe’, in Jennings, S and Vince, A (eds)

33 Medieval Europe 1992. Volume 3: Technology Küçükerman, O 1988 Glass Beads: Anatolian Memmi, I (ed) Advances in Archaeometry. and Innovation. York: Soc Med Archaeol, Glass Bead Making. Istanbul, Turkey. Turkish Development and Use of Scientifi c Techniques York Archaeol Trust and U York, 169–74 Touring and Automobile Association (Proceedings of the 37th International Symposium on Archaeometry, Siena). New Hirst, S 2000 ‘An approach to the study of Kunicki-Goldfi nger, J 2008 ‘Unstable historic York: Springer Anglo-Saxon glass beads’, in Price, J (ed) glass: symptoms, causes, mechanisms and Glass in Britain and Ireland AD 350–1100. conservation’. Rev Conserv 9, 47–60 Pellatt, A 1849 Curiosities of Glass Making. Brit Mus Occas Pap 127. London: Brit Mus London: David Bogue P, 121–30 Lee, E 2006 Management of Research Projects in the Historic Environment. The Pollard, A M and Heron, C 1996 ‘The Hoover, H C and Hoover, L H (eds) 1950 MoRPHE Project Managers’ Guide. Swindon: chemistry and corrosion of archaeological Georgius Agricola. De Re Metallica. New English Heritage glass’, in Pollard, A M and Heron, C York: Dover Archaeological Chemistry. Cambridge: Roy Soc Linford 2006 Archaeomagneic Dating. Chem, 149–95 Hunter, J R and Heyworth, M P 1999 The Guidelines on producing and Interpreting Hamwic Glass. CBA Res Rep 116. York: CBA Archaeomagnetic Dates. Swindon: English Price, J 1991 ‘Decorated mould-blown glass Heritage tablewares in the 1st century AD’, in Newby, IFA 2001 Standard and Guidance for the M and Painter, K (eds) Two Centuries of Art Collection, Documentation, Conservation Louw, H 1991 ‘Window-glass making in and Invention. London: Soc Antiq London, and Research of Archaeological Materials. Britain c 1660–c 1860 and its architectural 56–75 Reading: Inst Field Archaeol impact’. Construction Hist 7, 47–68 Price, J 2002 ‘Broken bottles and quartz-sand: MacGowan, K 1996 ‘Barking Abbey’. IFA 2008 Standard and Guidance for glass production in Yorkshire and the north Current Archaeol 13, 172–8 Archaeological Field Evaluation. Reading: in the Roman period’, in Wilson, P and Price, Inst Field Archaeol J (eds) Aspects of Industry in Roman Yorkshire McGrath, R and Frost, A C 1937 Glass and the North. Oxford: Oxbow Books, 81–93 in Architecture and Decoration. London: Jackson, C M 2005 ‘Making colourless glass Architect P in the Roman period’. Archaeometry 47, Price, J and Cottam, S 1998 Romano-British 763–80 Glass Vessels: A Handbook. York: CBA Miller, I 2007 ‘Percival, Vickers and Co. Ltd: the archaeology of a 19th-century Jackson, C M, Smedley, J W and Booth, C Shepherd, J and Wardle, A 2009 The Glass Manchester fl int glass works’. Indust M 2005 ‘Glass by design? Raw materials, Workers of Roman London. London: Mus Archaeol Rev 29, 13–29 recipes and compositional data’. London Archaeol Archaeometry 47, 781–95 Muspratt, S 1860 Chemistry. Theoretical, Shortland, A, Schachner, L, Freestone, I Practical and Analytical. Glasgow: Jennings, S 2005 ‘Anglian glass from recent and Tite, M 2006 ‘Natron as a fl ux in the Mackenzie and previous excavations in the area of early vitreous materials industry – sources, Whitby Abbey, North Yorkshire’. Annales du Pape, T 1934 ‘Medieval glassworkers in beginnings and reasons for decline’. J Archaeol e 16 Congrès de l’Association Internationale North Staff ordshire’. Trans North Staff Field Sci 33, 521–30 pour l’Histoire du Verre, London 2003. Club 68, 74–121 Nottingham: AIHV, 207–9 Smedley, J W, Jackson, C M and Booth, C A Newton, R and Davison, S 1996 Glass 1998 ‘Back to the roots: the raw materials, Johnson, S 1816 ‘The Works of Samuel Conservation. Oxford, Butterworth- glass recipes and glassmaking practices of Johnson LL.D. 4th Volume’. London: The Heinemann Theophilus’, in McCray, P and Kingery, W Rambler 9, April 17, 1750, 56 D (eds) The Prehistory and History of Glass Paynter, S 2008 ‘Experiments in the and Glassmaking Technology (Ceramics and Kenyon, GH 1967 The Glass Industry of the reconstruction of Roman wood-fi red Civilisation 8). Westerville, Ohio: American Weald. Leicester: Leicester U P glassworking furnaces: waste products and Ceramic Soc, 145–65 their formation processes’. J Glass Stud 50, Knight, B 1996 ‘Excavated window glass: a 271–90 Sode, T and Kock, J 2001 ‘Traditional raw neglected resource?’, in Roy, A and Smith, glass production in northern India: the fi nal P (eds) Archaeological Conservation and its Paynter, S forthcoming ‘The importance stage of an ancient technology’. J Glass Stud Consequences. Preprints of the Contributions of pots: the role of refractories in the 43, 155–69 to the Copenhagen Conference, 26–30 August development of the English glass industry 1996. London: Internat Inst Conserv Hist during the 16th /17th centuries’, in Taylor, M and Hill, D 2008, ‘Experiments Artistic Works IIC, 99–104 Ignatiadou, D and Antonaras, A (eds) in the reconstruction of Roman wood-fi red Annales du 18e Congrès de l’Association glassworking furnaces’. J Glass Stud 50, Krupa, M and Heawood, R 2002 The Internationale pour l’Histoire du Verre 249–70 Hotties: Excavation and Building Survey (Thessaloniki). AIHV at Pilkingtons’ No. 9 Tank House, Tennent, N 1999 The Conservation of St. Helens, Merseyside. Lancaster: Paynter, S and Dungworth, D forthcoming Glass and Ceramics. Research, Practice and Lancaster Imprints 10 ‘Recognising frit: experiments producing Training. London: James & James (Science post-medieval plant ash glass’, in Turbanti- publishers) Ltd

34 Tite, M, Pradell, T and Shortland, A 2008 ‘Discovery, production and use of tin- based opacifi ers in glasses, enamels and glazes from the late Iron Age onwards: a reassessment’. Archaeometry 50, 67–84

Tyler, K and Willmott, H 2005 John Baker’s Late 17th-century Glasshouse at Vauxhall. London: Mus London

Tyson, R 2000 Medieval Glass Vessels Found in England c AD1200–1500. CBA Res Rep 121. York: CBA

Van den Bossche, W 2001 Antique Glass Bottles. Their History and Evolution (1500–1850). Woodbridge, Suff olk: Antique Collectors’ Club

Vince, A 1977 Newent Glasshouse. Bristol: CRAAGS

Waterbolk, H T 1971 ‘Working with radiocarbon dates’. Proc Prehist Soc 37, 15–33

Watkinson, D and Neal, V 2001 First Aid for Finds. Rescue / UKIC Archaeology Section

Welch, C M 1997 ‘Glass-making in Wolseley, Staff ordshire’. J Post-Med Archaeol 31, 1–60

Welch, C and Linford, P 2005 ‘Archaeomagnetic dating of medieval and Tudor glassmaking sites in Staff ordshire, England’. Annales du 16e Congrès de l’Association Internationale pour l’Histoire du Verre, London 2003. Nottingham: AIHV, 210–13

Whitehouse, D 2010 Medieval Glass for Popes, Princes and Peasants. Corning, NY: The Corning Museum of Glass

Willmott, H 2002 Early Post-Medieval Vessel Glass in England c 1500–1670. CBA Res Rep 132. London: CBA

Wills, G 1974 English Glass Bottles for the Collector. Edinburgh: Bartholomew

Witt, C, Weeden, C and Schwind, A P 1984 Bristol Glass. Bristol: Bristol and West

Wood, E S 1965 ‘A medieval glasshouse at Blunden’s Wood, Hambledon, Surrey’. Surrey Archaeol Coll 62, 54–79

Wood, E S 1982 ‘A 16th-century glasshouse at Knightons, Alfold, Surrey’. Surrey Archaeol Coll 73, 1–47

35 C ontributors These guidelines were written and compiled by Sarah Paynter and David Dungworth with contributions by Rachel Tyson, Karla Graham and Mark Taylor and David Hill (Roman Glassmakers).

Acknowledgements We are grateful to the following people for commenting on, and improving, the text: Justine Bayley, Sarah Jennings, Lisa Moffet, Dominique de Moulins, Andrew David, Andy Hammon, Shane Gould, Jenny Price, Caroline Jackson, Rachel Tyson, Sue Stallibrass, Gill Campbell, Chris Welch, Tom Cromwell, Matt Canti, Paul Stamper, Edmund Lee, Karla Graham, Jim Williams, Ian Miller, David Martlew, John Henderson, Colin Brain, Mark Taylor and David Hill (Roman Glassmakers), Angela Wardle, Bob Jones, Martin Railton and Nigel Cavanagh.

We would like to thank the following Front cover: (top left) Removing the glass cone for a English Heritage is the Government’s people and organisations for providing cathode ray tube from a hand press, comprising a plunger and statutory advisor on the historic mould, at Osram glassworks, Newcastle upon Tyne, mid-20th illustrations: Justine Bayley, Sarah century (reproduced by permission of English Heritage.NMR); environment. English Heritage provides Jennings, Christopher Welch, John (top middle) A Roman moil from London, showing a stepped expert advice to the Government about c Vallender, Birmingham Archaeology profi le, 13mm diameter (photo by Andy Chopping/MOLA); matters relating to the historic environment (top right) A glassworker reheating a glass object in a replica and Dudley MBC, YAT, NMR, Ordnance Roman furnace by Mark Taylor and David Hill; (lower left) and its conservation. Survey, David Adams and John Burnham An 18th- to 19th-century glass cone under excavation at (Warwickshire Archaeological Research Dudley Flint Glassworks, Stone Street Square, West Midlands For further information and copies of this (Birmingham Archaeology and Dudley MBC); (lower right) Trust), Andy Chopping (Museum of A large crucible fragment from an early 16th-century publication, quoting the Product Code, London Archaeology), Ian Freestone wood-fi red furnace at Bagot’s Park, Staffordshire (photo by please contact: and Jerzy Kunicki-Goldfinger (Cardiff David Crossley); (lower left) A rectangular-plan, 17th-century glasshouse at Shinrone, Ireland, with surviving vaulted University), Mark Taylor and David Hill sandstone super-structure. The small holes in the vault are for English Heritage (Roman Glassmakers), Ian Miller (Oxford smoke to escape; there was no chimney. The fi re trench runs Customer Services Department Archaeology North), Colin Brain, David through the arched openings at each end with low sieges on PO Box 569 either side. Gases from the wood fuel have reacted with the Crossley and Rachel Tyson. stone furnace walls to make a blue glaze-like surface over Swindon SN2 2YP the inside surfaces. The side walls, which originally would have had gathering holes in them, have not survived (photo by telephone: 0870 333 1181 Chris Welch). e-mail: [email protected] Back cover: Bull’s eyes used decoratively in glazing.

Published June 2011

Edited and brought to press by David M Jones, English Heritage Publishing Designed by Pauline Hull

Product Code 51642

36 If you would like this document in a different format, please contact our Customer Services department: Telephone: 0870 333 1181 Fax: 01793 414926 Textphone: 01793 414878 E-mail: [email protected]