­chapter 2 Early History of Stained

Francesca Dell’Acqua

The destruction of a large number of medieval glazed light, and the interaction between natural and artificial windows in the 18th century can be attributed both to light. An emphasis on materiality, combined with the the desire for more light in buildings, reflecting the in- study of past building practices, as well as specific aesthet- tellectual and political desire to overcome the obscu- ic and cultural ambitions, currently informs the research rantism of past ages, and to the turmoil of the French on the origins and later developments of .4 Revolution. This destruction generated reflections, mu- seum displays, and scholarship on the history of stained glass. According to the early histories of western stained 1 Roman Glass glass, written between the late 18th and 19th centuries, the origins of the technique remained unknown, thus it In his famous treatise written between 30–​15 b.c. under was hard to explain how the medium developed before the first Roman emperor , suggests culminating in the masterpieces of the Gothic period.1 methods to increase the quantity and quality of natural French, English, and German scholars collected written light when planning a room, especially in densely pop- and material evidence to demonstrate that medieval ulated cities.5 Windows had the combined functions stained glass had been invented in their own countries. of letting in natural light (lumen), allowing ventilation Despite having divergent opinions, they actually provid- (aer), and possibly opening up to a view (prospectus), ed converging evidence, which demonstrated that the especially in the triclinia, i.e. the dining-​rooms of sub- origins of stained glass were to be situated in an area urban or rustic .6 A few centuries later, in the Late across present-​day France and Germany.2 So, why, when, Empire, public Roman buildings and especially basilicas how, and what was used to screen the windows in build- would be characterised by larger windows placed in or- ings before the 11th century? Archaeological finds made derly series, which allowed in plenty of natural light.7 in the last few decades have confirmed what was hinted The adoption of glass panes in the window grilles and by textual sources and by occasional finds: glass was in- their setting as close as possible to the surface of the in- deed employed in windows well before the High Middle terior walls produced the effect of diffused light, which Ages, although it was cut in geometrical shapes and was enhanced the lavish marble and mosaic revetment of not decorated with any painting.3 the walls.8 Light, natural or artificial, is essential in shaping inner Glass, though, does not appear in Vitruvius’s treatise spaces and in determining their perception. Sensations as a window screening device. In fact, glazed windows such as warm, cold, spacious, gloomy, airy, oppressive, have not been found in private and public buildings of and so on, are indeed largely determined by natural and the before the 1st century a.d. The well-​ artificial illumination. This was well understood already dated evidence offered by is indicative of the in Classical Antiquity, when builders seem to have taken fact that glazed windows did not become common be- into account the direction and variability of sunlight, the fore the second half of the 1st century a.d. The necessi- number and shape of the openings, the type of window ty of having well-​lit public spaces such as baths, as well screens affecting or favouring the penetration of natural 4 For a critique of the theoretical approaches of earlier studies on the use of stained glass in buildings of the past, see Hediger and 1 For more on this topic Kurmann-​Schwarz, Ch. 20 in this volume. Schiffhauer, “Werkstoff Glas”. 2 Éméric-​David, Discours historiques sur la peinture moderne; 5 Vitruvius, On Architecture, 6.6.6-​7, The Loeb Classical Library 280, id., Histoire de la peinture au Moyen Âge, pp. 38–​39, 79–​80; vol. 2, pp. 42–​45. Didron, “Histoire de la peinture sur verre”; Lübke, Über die al- 6 Vitruvius, De architectura, 6.3.10, trans. Granger, The Loeb Classi- ten Glasgemälde der Schweiz; Nordhoff, “Die ältere Glasmalerei”; cal Library 280, vol. 2, pp. 32–​33; ibid., 6.4.1, pp. 34–​35. Westlake, A History of Design in Painted Glass; Oidtmann, Die 7 Günter, Wand, Fenster und Licht, pp. 66–​76 presents a catalogue of Glasmalerei, vol. 2, pp. 33–​44; see also Dell’Acqua, “Entre fantaisie late Roman buildings with the measurements of their windows. et archéologie”. For recent work based on his, see Eder, Licht und Raumform, and 3 For an overview, see Whitehouse, “Window-​glass between the Köhler, Basilika und Thermenfenster. first and the eighth centuries”. 8 Günter, Wand, Fenster und Licht, p. 7ff.

© Koninklijke Brill NV, Leiden, 2019 | DOI:10.1163/9789004395718_004​ 24 Dell’Acqua as the desire of having a lavish dining-​room with a vista and shiny. Normally cylinder glass can also be recognised over a pleasing landscape, or peristylia (i.e. inner court- because it contains elongated air bubbles, revealing the yards, screened by glass in winter), is attested by Roman direction in which the glass bulb was blown. authors. There are few remains of Roman glazed win- The blowing technique, which was also employed to dows, because glass fragments were normally discarded fashion vessels by blowing them into moulds, acceler- if found during the investigation of archaeological sites. ated the production of window glass and made it pop- Only recently has the adoption of different investigation ular all over the Mediterranean. In the eastern regions and cataloguing procedures produced new informa- of the Roman Empire another glass-​blowing technique tion on these objects from every corner of the Roman for producing window panes was invented and dissemi- Empire between the 1st and the 5th centuries.9 In this nated. It consisted of piercing, opening, and twirling the period, the glass industry had a cross-Mediterranean​ blown bulb of glass to shape it as a disk (“crown-​blown span. In his Naturalis Historia, Pliny mentions the glass disk”). As the centre of the disk remained attached to the at the mouth of the river Belus in Palestine, and the river blowing-​pipe during the modelling, it was considerably Volturno in Campania as the best for producing glass;10 thicker than the rest of the disk, and is called a “bull’s however, scientific analyses have confirmed that the eye” or omphalos, i.e. navel. The centre of the disk, con- Syro-​Palestinian coast was the major glass-​production sidered less valuable because of its irregular aspect, al- area. From there, glass was exported as ingots or cullet lowing less light in and blurring the vision, became the to the West where it would be modelled into objects.11 standard glass pane used in windows of northern Europe But what determined the wide adoption of window during the Late Middle Ages and the Early Modern peri- glass in the Roman Empire? Flat glass had been pro- od.15 It is very rare, however, in early medieval contexts. duced earlier by pouring molten glass onto rectangular trays and distributing it with a spatula towards the edges, although the result was thick and opaque panes. In Pal- 2 Early Medieval Evidence estine during the 1st century b.c. glassmakers started ex- perimenting with a new technique. This involved the use One of the earliest written sources about glazed win- of clay rods (later substituted with ) or blowpipes, dows is the series of verses praising the interior decor through which they would collect a bulb of molten glass of the basilica of St. Paul Outside the Walls in , from a vessel, blow air into it, and manipulate it into a cy- promoted by the Emperor Theodosius and his family be- lindrical shape, which was then pierced and widened.12 tween the late 4th and early 5th century. In a collection This method was still in use in the West in the 12th centu- of poems dedicated to Spanish and Roman martyrs, the ry, as it is attested by a treatise on The Various Arts, writ- court poet Prudentius describes the colours of the win- ten by a monk who calls himself Theophilus, active in dows of St. Paul’s as like flowery meadows in spring.16 It northern Germany between Cologne and Paderborn.13 is not possible to infer from the passage if the windows He says that the cylinder was cut when cold and then had any figural pattern. Absence of specific evidence reheated in order to be flattened on a polished surface.14 suggests that they were non-​figural, allowing in natu- This cooling phase produced a different appearance be- ral light as a symbol of God. The apostles and prophets tween the recto and the verso of the cylinder: the former painted on the segments of wall between the windows looks like rippled skin because of cooling more quickly in the main paleochristian basilicas of Rome, flanking in contact with the air, and the latter appears smooth and introducing the Light of God, made the most appro- priate complement to the non-​figural – ​albeit wonder-

fully coloured –​ glazed windows.17 9 Dell’Acqua, “Le finestre invetriate nell’antichità romana”. 10 , Naturalis Historia, 36.65, trans. Eicholz, The The appreciation of polychromy expressed by Pru- Loeb Classical Library 419, vol.10, pp. 148–51;​ Freestone, dentius is in keeping with the contemporary aesthetics,

“Pliny on Roman glassmaking”. as expressed by poetry and visual arts.18 Floral tropes, 11 Freestone, Gorin-​Rosen, and Hughes, “Primary glass from Israel”; Freestone, “”. 12 Israeli, “The invention of blowing”; Stern, “Roman ”. 15 See the bull’s eye glass shutters in the Hours of Mary of 13 On the debate about the identity of Theophilus, also in light Burgundy, illuminated before 1482 in Stokstad and Cothren, of the manuscript tradition, see the recent study by Gearhart, Art History, p. 568, fig. 18-​6. Theophilus, and discussion by Brigitte Kurmann-​Schwarz, 16 Prudentius, Peristephanon Liber, Hymn 12: Passio Apostolorum Ch.20 in this volume. Petri et Pauli, vv. 53–​54 (pp. 420–23);​ Dell’Acqua, “Illuminando 14 Theophilus, De diversis artibus, ii, 6, ed. and trans. Dodwell, colorat”, pp. 101–​02. pp. 54–​55. For more on the making of the window, see Brown, 17 Kessler, Old St Peter’s, p. 76. Ch. 1 in this volume. 18 See Roberts, The Jeweled Style.