1

RECOGNITION OF STONE PROVENANCE AND CASE HISTORIES OF DETERIORATION OF TWO ANCIENT TOMBSTONES FROM AND HANOVER (NORTHERN )

VISSER, H., GERVAIS, A. ,

Deutsches Zentrum fOr Handwerk und Denkmalpflege, Au~nstelle Hannover, Leitstelle KOstenlander, Schamhorststr. 1, D-30175 Hannover GERVAIS,K., Enzianweg 9a, D-30880 Laatzen NEUMANN, H.-H. Amtliche MaterialprOfungsanstalt (MPA Bremen), Paul-Feller-Sir. 1, D-28199 Bremen ROSCH, H. Bundesanstalt fOr Geowissenschaften und Rohstoffe (BGR), Stilleweg 2 D-30655 Hannover WENDLER, E. Fachlabor fOr Konservierungsfragen in der Denkmalpflege, Keyserlingstr. 33 b, D-81245 MOnchen

SUMMARY In northern Germany various quartz sandstone (orthoquartzite) types were used as building­ and ornamental stones since medieval times. One of the most important types being from the Upper Elbsandsteingebirge, SE of . The deterioration behaviour of this stone, and also possibilities to distinguish it from other quartz sandstone types of the region, are shown in this paper. At the southern border of Hamburg, in Kirchwerder, Renaissance tombstones are exposed unsheltered, under very wet conditions. Here the stones are overgrown by lichens and algae. A totally different ecological situation can be shown with an example from the Jewish cemetery "An der Strangriede" in Hanover, where on a tombstone from the year 1918, under extreme imission conditions, the surface is covered with gypsum crusts, lead paint remnants and palmierite K 2 Pb(SQ4 ) 2 .

Introduction

In the Pleistocene- and Holocene- covered plains of northern Germany, no local sandstone resources are available and bricks are a dominant constructing material for entire buildings. Therefore, ornamental and building stones had to be imported. Here since ancient times portals, tombstones and sculptures were made from Mesozoic from the highlands to the south of the plains, or from Paleozoic stones, imported from in Scandinavia. Mezozoic sandstones used for this purpose are predominantly Cretaceous quartz sandstones, less frequently Buntsandstein (Lower Triassic}, and some local types. Occurrences of Cretaceous quartz sandstones are widespread in the highlands south of the northern Germany lowlands, reaching from Bentheim next of the Netherlands border in the west, to the Elbe Sandstone area at the Czech borderland in the east. In old trade centres like Hamburg many different sandstone types from far away were mixed by trade since medieval times. Due to their widespread geographic occurrences and similar petrographical appearence, the determination of the provenance of certain quartz sandstone varieties is rather difficult. Therefore, a stone register for quartz sandstones used for monuments is felt most important. It should contain information about provenance, typical fingerprints for recognition, and phenomena. We are preparing such a project, 2 and the two case studies presented here are an anticipation for our quartz sandstone project, of course with still rather uncomplete data.

Quartz sandstone building and ornamental stones in northern Gennany The two most famous quartz sandstones used in northern Gennany are _ Elbe sandstone quarried in the south of Dresden, eastern Gennany. They are of and Turonian age (Upper Cretaceous) and: - wealden sandstone from the south of Hanover (Berriasian age, lower Early Cretaceous) with its well known main type, the Oberkirchen Sandstone.

Varieties of the Elbe Sandstone Elbe sandstones are quarried in the Elbe Sandstone mountains since medieval times. A lot of this material has been shipped down the River Elbe to Hamburg, and later it has been transported by railway. Therefore, the Elbe Sandstone varieties have been used very frequently as ornamental and building stones in northern Germany. There are several types of Elbe Sandstone varieties: Coarse-grained quartz sandstone, well cemented and ,therefore, very resistant, for example the Postelwitzer Sandstone and the Pasta Sandstone, fine-grained sandstone with some argillaceous flasers, called Cotta Sandstone, fine-grained quartz sandstone, with only very low content of argillaceous material. This type is found in the quarry of Reinhardtsdorf for example. Since these lithologies were used in many regions as ornamental stone, for example tombstones, it is sometimes difficult to distinguish these fine-grained quartz sandstones from one another or even from those of different provenance (e.g. Wealden ).

Tombstones in Hamburg Many ancient tombstones from the Hamburg area were made of fine grained quartz sandstones, usually Elbe Sandstone transported down the River Elbe. Some old tombstones of that kind are found in different Christian and Jewish cemeteries of Hamburg, but the most famous site is the cemetery of Hamburg-Kirchwerder. In that village, at the southernmost part of state of Hamburg, 94 large tombstones, dated from the 16th up to the 18th century, can still be found. They are situated in a rural surrounding, far outside of Hamburg city, on the northern bank of the River Elbe. For hundreds of years, the big tombstones lay flat on the ground, under very wet conditions, but in the last decades (1950ies) most of them were placed upright at the border of the cemetery. The exposure of the majority of the tombstones to rainfall supports the growth of lichens. This exposure prevents major accumulations of various kinds of salts but causes frost damages during winter time. A typical tombstone from Kirchwerder (Fig. 1), dated from 1610, is showing the Fall of Man with Adam and Eve and the tree of knowledge of good and evil. The totally unsheltered surface shows that widespread loss of material has happened, mainly by loss of sand grains, which causes ornament structures to become indistinct. In some parts loss of a thin stone scale, about 1 mm thick, has happened at a first state of weathering, but no actual loose scale could be found, and there is no visible sign of a second scale developpir.g. At the nowadays weathering surface the stone material is rather resistant actual losses are continuing at a very slow rate on the normal stone surface _ but big actuai losses are due to stone break off caused by rosting iron reinforcement. ~om~ of the ~00 year old tombstones still show ~elatively well preserved surface structures, in spite of their unfavourable exposure, thus proving a good lithological quality. 3

Origin: After inspection of the sandstone varieties at the locus typicus the tombstone's origin can be traced back with a very high probability to those Elbe Sandstone quarries, from which fine grained quartz sandstone types had been exploited (e.g. from Reinhardtsdorf). Many parameters of the tombstones, e.g. composition and texture, are similar to the Elbe Sandstone, but many of such characteristics are also found in other quartz sandstone varieties from different areas. Therefore, it is interesting to collect some more specific infonnation. A heavy analysis showed abundant tounnaline and garnet. However, the observed high garnet content in the investigated sandstone has never been reported before from Elbe Sandstone varieties. BEEGER (1962) reports the occurrence of low garnet contents. Similar quartz sandstones from other provenances like the Wealden sandstone varieties do never show a significant content of garnet. Therefore, the most probable origin for the Kirchwerder tombstones, according to our preliminary results, is from the Elbe Sandstone region. The authors are grateful for further infonnation about deposits of garnet-bearing quartz sandstones.

A tombstone in Hanover A very different situation is found in a much younger Jewish cemetery in Hanover. There, beginning with the year 1864, tombstones of very different provenance do occur, some of them showing many lithological similarities with those of the Elbe Sandstone area - especially with the Cotta Sandstone types. However, we should keep in mind the general difficulty of the "quartz sandstone origin" problem. The investigated tombstone, dated from 1918, is a fine-grained sandstone, containing thin flasers of argillaceous matter. The colour is grey, light brown and in parts weekly red by lepidokrokite (X-ray analysis, BGR Hanover). This colour has so far never been described before from the Cotta Sandstone variety, so the origin was doubtful at the beginning of our study. Accessory minerals are: 0.5% potassium felspar and 2 % , and some variable amount of clay minerals (more than 10 % and illite). The illite is concentrated in mud flasers. A Jnoceramus sp. proves an Upper Cretaceous age of the ornamental stone. Analysis of transparent heavy minerals reveal for both the tombstone and a sample from Cotta Sandstone type from the quarry Neundorf mainly zircon, rutile and tounnaline (schoerl of prevailing brown or green colours) and minor amounts of staurolite, anatase and/or brookite, epidote and chrompicotite (a dark red transparent chromite-spinell). The results show almost perfect congruence with the heavy mineral spectrum of the Cotta Sandstone. Next to this Hanover cemetery a non-ferrous metal foundry was working for decades causing a high industrial pollution to its surroundings. In many parts of the cemetery original stone surfaces are covered with intense black crusts. The described tombstone consists of three different single stones and has more complicated exposure conditions with an exposed stone roof and more ore less sheltered lower parts (Fig. 4). The roof stone has the best quality and hardly shows any loss of material, but thick black crusts in sheltered parts. In the sheltered parts below, either black crusts or losses of original surface can be found. Parts of the original surface have been destroyed, pieces of stone disaggregate in the fonn of scaling. Only then, the original light brown stone colour with some brown stipples becomes visible. 4

Below the recent surface there is a less resistant weathering zone which is approximately 5- 1o mm thick. Drilling resistance measuring shows two different types of resistance profiles, which are shown in Fig. 7. The profiles found in the middle stone and the columns show discontinuous loss of resistance, typical for sandstones which loose material in the form of scales (Fig. 7a and 7b). The roof stone shows a continuous loss of resistance, proceeding from the surface (Fig. 7c). This covering stone does not show loss of scales. The tombstone must have been covered originally by a lead white paint, because lead containing compounds can be found in the upper part and traces of the mineral palmierite (K2Pb(S04)2 ) in the lower part of the stone. Investigations by SEM suggest treatment with waterglass or silicic acid ester. The surfaces of quartz grains and the Pb-containing pigment are covered with silica gel. EDX analysis supports the evidence of Si but not that of K. It is suggested that palmierite might have been formed by the reaction of weathering lead­ white paint with potassium-waterglass (HERM et al. 1993). The processes and reactions are still not well known and under discussion. Due to the very complex surface conditions, a restoration of the tombstone will be very difficult. This is the setting of tasks of two actual projects, with the aim of conservation of tombstones on Jewish cemeteries in Berlin and in Hanover (STADLBAUER, EHLING, KRUMBEIN, SCHADLER-SAUB, WENDLER, SCHUH & BLUM, see this proceedings of the 8th International Congress on Deterioration and Conservation of Stone, Berlin 1996).

Comparison of weathering of the two tombstones On the tombstones in Kirchwerder, in the main part of the surface you can see the effect of about 400 years very slowly advancing weathering. Sandstone decomposition takes place mainly loosing grain by grain, less frequently by loss of scales. At the described example in Hanover, two types of weathering behaviour can be found . The roof stone does not show much loss of material, but already a continuous loss of resistance, to a certain degree, proceeding from the surface. This type, in the weathering behaviour, has some similarities with the above mentioned quartz sandstones in Hamburg Kirchwerder. The stones in the lower part of the monument reveal a higher velocity of weathering, with appreciable losses of material in 70 years and now rapidly advancing disaggregation by loss of scales .. This is in part due to special exposure conditions, in part due to the reduced durability of the clay-rich stone material. The cover of gypsum crusts, remnants of the lead white paint, new lead containing compounds and silica gel might additionally favour the loss by scaling instead of decomposition of the sandstone grain by grain. Some bacteria, algae and fungi are found on the stone surface, but no lichen could settle in the heavy metal containing environment.

Acknowledgement Investigations on the Jewish cemetery in Hanover are supported by the DBU, Federal Republic of Germany (DBU project nr. 04338) and by the Union of Jewish Communities in Lower . Prof. H. Kulke, Institute of Geology, Technical University of Clausthal is thanked for critically reviewing the manuscript.

References:

SEEGER, H.-D. (1992) .- Petrographische und technische Eigenschaften des Labiatu' ssan d st eines· 1m. Raum Konigstein-Cotta.- Jb.Staatl.Mus.Mineral.Geol.: 9-68; Dresden. GRUNERT, S. (1986): Der Sandstein der sachsischen Schweiz.-Abh. d. Staatl. Mus. f. Min. u. Geol. Dresden, Bd. 34, VEB Dt. Vert. f. Grundstoffindustrie, Leipzig 1986. GRUNERT & KUTSCHKE (1995): Der Elbsandstein als Werk- und Dekorstein E k · . .- x urs1on 83, in: 5

Exkursionsfi.ihrer zur Sediment '95, 10. Sedimentologentreffen 24.-28. Mai 1995 an der TU Bergakademie Freiberg. HERM, Ch., KLEMM, D.D., SNETHLAGE, R. (1993) .- Untersuchungen zur Verwitterung von Farbfassungen auf Natursteinen.- Jahresberichte aus dem Forschungsprogramm Steinzerfall­ Steinkonservierung 1991 (Hrsg: R.Snethlage ), : 53-61 ; Berlin. VOIGT, T. (1994): Faziesentwicklung und Ablagerungssequenzen am Rand eines Epikontinentalmeeres - die Sedimentationsgeschichte der sachsischen Kreide.- unveroff. Diss. TU Bergakademie Freiberg. VOIGT, T. (1995): Sedimentstrukturen und Faziesentwicklung in siliziklastischen KOstensedimenten (Cenoman und Turon der Sachsischen Kreide).- Exkursion A2, in: ExkursionsfOhrer zur Sediment '95, 10. Sedimentologentreffen 24.-28. Mai 1995 an der TU Bergakademie Freiberg. WENDLER, E. & SADLER, L. (1996 in press): Die Bohrwiderstandsmessung als zerstorungsarmes PrOfverfahren zur Ermittlung des Festigkeitsprofils an verwitterter Bausubstanz. Normierungsverfahren im Labor und Fallbeispiele am Objekt. 4th International Colloquium 'Werkstoffwissenschaften und Bausanierung", Technische Akademie Esslingen. 6

Fig. 1: Tombstone, dated .1 610, "The Fall of Man" .with Adam and Eve and the tree of knowledge, in Hamburg-Kirchwerder. (Height of tomb~~ne : approx1mate_ly 2 m) photographed by: T.Trapp, 1995; descnpt1on by: A. Gervais, 1995.

Exposition: detached; at hand a fi rm co~nect i o n with a wall reaching up to the middle of the tombstone; to the side surrounded by trees; backside exposed to a road . Material: fine grained quartz sandstone with large remnant of plant fossil and trace (e.g. burrow structures) on the bedding plane. Front part: relief ornaments decorating the four edges; at the right, the left, and the lower margins and in the lower part of the tombstone are letters cut into the stone. Rear part: natural stone surface with trace fossils (burrow structures), plant fossil: Calamites sp.(length about 30 cm) . A diagonal fissure separates the upper from the lower part of the tombstone; the corrosion process of the iron reinforcement is causing stone break off. Diagnosis: loss of relief due to detachment of sand grains; the sculptured elements have lost their superior quality of the stone-mason-~or~ by w~athering ;_ th~ inscriptions have become illigible and threatened to be lost completely; colonisation by b1ogenes like lichen (see. Fig. 2) algae and fungi· in the lower part of the tombstone distinct traces caused by the drainage of rainwater. ' ' 7

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photographed by: T.Trapp, 1995

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Fig. 3: Thin section (25 µm thickness) of a quartz sandstone sample from the tombstone "The Fall of Man", Hamburg-Kirchwerder in translucent light. photographed by: H.Visser, 1995 description by: H.Visser & A Gervais, 1995 grain size: 60-140-180 µm mineral composition: quartz, rock fragments ( clay-/siltstone, fragments of sericite schist), kaolinite, ?magnetite. texture: intergranular contact of quartz-grains with plane contacts induced by diagenetic growth of quartz grains; intergranular porosity 15 vol.% of total sample (pore space filled with blue-stained resin); partly kaolinite is developed in the pore wedges;. characteristics: a dark dirty film on top of the weathered stone surface (most upper part). 8

Exposition: standing in front of the cemetery brick wall. Th~ s~all _ gap bety-1een tombstone and brickwall is filled up with rotten leaves, roots, and other recent deposits nch m organic matter. Material: fine-grained sandstone with argillaceous flasers; a shell impression of a marine fossil (lnoceramus sp.) was found . The sandstone is Elbe Sandstone, type Cotta Sandstone. The inscription plate consists of marble. . . Diagnosis: in parts the st~ne surface 1s covered wit~ bla_ck crusts containing gypsum, lead paint remnants and their weathenng products, soot etc. (especially in sheltered areas). Surface areas with loss of stone material show light grey or light brown colour of the deteriorated rock (major losses in the middle part above inscription, and at the lower part of the column right side). 9

I 0.1 mm

Fig. 5: Thin section (25 µm thickness) in translucent light of a sample from the tombstone No. 93/7 of the Jewish cemetery "An der Strangriede" in Hanover. photographed by: H. Visser, 1995 Pet:ography: A_rgi."aceous sandstone (lower part) covered by a nearly opaque crust (upper part). The crust consists mainly of palm1erite K2Pb(S04)2

I0.1 mm

Fig. 6: Thin section (25 µm thickness) in translucent light of a sample from the tombstone No. 9317 of the jewish cemetery "An der Strangriede" in Hanover. photographed by: H. Visser, 1995 Petrography (detail of a more argillaceous part): Between the quartz-grains occurs locally free pore space (stained blue), and partly argillaceous ground mass. In the middle of the micrograph newly crystallized kaolinite aggregates are visible. 10

drilling resistance [th/1 O] 8 ~---a

6 a1

4

2

0

8 b 6

4

2

0

8 c 6

4

2

" 0 5 10 15 20 25 depth (mm)

Fig. 7: Measuring drilling resistance at the tombstone nr. 93-7 on the Jewish cemetery "An der Strangriede" in Hanover. Measuring executed by E. Wendler, 1995.

Diagram a: resistance profile on the middle stone, on a location where stone scale have been lost. Diagram a1 : resistance profile on preconsolidated area, with the same exposure. In both sites a weak zone exists in 4-5 mm depth, which can be valuated as an indication for the ongoing formation of a second scale. Diagram b: resistance profile on a column, on a stone scale. A very thin but very hard scale is underlain by a thin weak zone. At a depth of 3-4 mm the material is resistant. Diagram c: resistance profile on the roof stone. Loss of resistance is proceeding continuously from the surface.