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The Conservation of AmberAuthor(s): David Thickett, Pippa Cruickshank and Clare WardSource: Studies in Conservation, Vol. 40, No. 4 (Nov., 1995), pp. 217-226Published by: Maney Publishing on behalf of the International Institute for Conservation ofHistoric and Artistic WorksStable URL: http://www.jstor.org/stable/1506496 .

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THE CONSERVATION OF AMBER

David Thickett, Pippa Cruickshank and Clare Ward

Summary-The British Museum (London) has extensive collections of amber artifacts. Analysis is carried out on amber for both authentication and provenancing. Infrared spectroscopy has been widely used in the past but other methods are becoming available. Several factors, including environmental conditions, contribute to the deterioration of amber, making it vulnerable to damage through handling. Where consolidation is required, the materials used must not interfere with possible future analysis. This paper considers the selection of resin and solvent mixtures for the consolidation of amber, as well as improved methods for storage and display. The materials recommended have well-known properties and can be removed from small samples prior to analysis.

Introduction

The British Museum in London has an extensive range of archaeological and historic amber artifacts. Amber was frequently used in jewellery, and there are many examples of beads, necklaces, pendants, brooches and fibulae in the collections, as well as carvings and containers. Very little has been published on the conservation of amber, and what is available gives rather negative and confusing advice [1, 2]. Some amber artifacts have suffered deterioration from chemical alteration, which results in increased fragility, and subsequently physical damage has occurred. Although some of the amber in the collections was provenanced by Curt Beck in the 1960s [3, 4], additional methods of provenancing are now available and further analysis may be carried out in the future. The importance of the amber collections in the museum and concern about the possible effect of any consolidants, adhesives and solvents on future identification and provenancing studies of amber [1] led to this research being carried out. As part of this work, conditions of storage were also considered.

Amber chemistry and analysis

Ambers are fossilized resins dating from the early Cretaceous (135-65 million years) to the Miocene (26-7 million years) periods. They occur in a number of locations, the major European source of amber being the shores of the Baltic Sea. Although the chemistry of all types of amber has not been completely elucidated, that of Baltic amber has been fully investigated. Its main constituent is a polyester formed from communol and communic and succinic acids. Slight differences in chemical composition between ambers have allowed methods of provenancing to be defined.

Received 11 January 1995

Analysis is carried out on ambers for both authentication and provenancing, which is important for the study of ancient trade routes. Many techniques have been used [5], of which infrared spectroscopy has been the most widely applied. This requires as little as 50gg of sample. The identification of a sample as amber is based on a terpenoid-type spectrum with additional absorptions due to exocyclic methylene groups occurring at 3095, 1625 and 880cm-'. It should be noted that both copal and sandarac also show these absorptions, but these materials can be distinguished easily from amber by their solubility in certain solvents. The region between 1100 and 1250cm-1 is used to discriminate between European ambers of Baltic and non-Baltic origin [6]. Baltic amber is unique in that it has a single absorption maximum near 1150cm-' and a broad shoulder between 1175 and 1250cm- .

Infrared spectroscopy has limitations as a technique for analysis of amber, since it cannot distinguish between all types. This technique is also sensitive to contamination, for example by conservation materials, making identification, and espe- cially provenancing, difficult. The sample size is extremely small and would be taken from the surface. Since the surface of deteriorated amber can be porous, a sample may take up a relatively high pro- portion of consolidant. This, coupled with the sen- sitivity of the conditions used for provenancing, means that even the small amounts of conservation materials used for consolidation can have an effect on the infrared spectrum of amber.

More advanced techniques such as pyrolysis-gas chromatography-mass spectrometry are reported to be able to distinguish between all amber types [7]. Methods based on gas chromatography can easily distinguish between amber and modern synthetic resins used as conservation materials; hence these would not affect analysis using such techniques.

Studies in Conservation 40 (1995) 217-226 217



D. Thickett, P. Cruickshank and C. Ward

However, because of its wide availability, infrared spectroscopy is still often used for amber analysis and has been used in this study.

Degradation of amber

Amber degrades with addition of oxygen across the double bonds of the exocyclic methylene groups. This degradation can lead to one of two physical changes: a surface crazing (Figure 1), resulting in areas becoming weakened and susceptible to loss; and surface powdering (Figure 2), also resulting in weakening and loss of material. The British Museum's collection is used for study and research purposes and therefore sometimes needs to be han- dled. Degraded ambers may require consolidation to prevent mechanical damage through handling, and detached fragments need to be reattached. In addition, amber retrieved from archaeological excavations is often badly weathered and deteriorated. However, as it is important that any conservation treatment does not interfere with future analysis of the amber, non-interventive methods should always be considered first. Good storage and display methods may eliminate the need for consolidation.

Figure 1 Detail of amber beads showing surface crazing.

1 Crm

Figure 2 Detail of surface powdering of an amber bead.

Review of past and current conservation treatments

A wide range of methods and materials has been used to conserve amber. 'Oil of amber' is often recommended as a suitable consolidant [2, 8]. Its composition is not well known. It may be a distillate of amber [9], or amber in a solvent such as linseed oil or aspic oil. Copal-derived 'oil of amber' is also available. Other varieties of natural terpenoid resin, including dammar, have also been utilized to consolidate amber [1, 10, 11].

Waxes, such as paraffin wax and beeswax, have been used as consolidants [1], and there are examples in the British Museum collections of the use of waxes both to consolidate and to fill missing sections of amber [11].

Synthetic resins used as consolidants include polyvinyl acetates and acrylic resins. Synacryl 9122X (an acrylic resin) in dimethylbenzene (xylene) has been favoured in Denmark [12]. Paraloid B72 (an ethyl methacrylate methyl acrylate copolymer) in dimethylbenzene has recently been the preferred consolidant and adhesive for amber at the British Museum. Vacuum pressure has been applied to aid the deeper penetration of a consolidant into the amber [10, 12].

The partial solubility of amber in certain solvents, such as propanone (acetone) or potassium hydroxide solution, has been utilized to make joins by softening the edges of the amber. Heat in con- junction with linseed oil has also been used to join amber sections [13].

Waterlogged amber from archaeological excavations presents its own specific problems. Methods that have been used to dry out the amber prior to treatment include gradual dehumidification [14], desiccation under vacuum [12], and dewatering in propanone [15]. Consolidants applied to wet amber

218 Studies in Conservation 40 (1995) 217-226



The conservation of amber

include solutions of polyethylene glycols and polyvinyl acetate emulsions. Waterlogged amber has also been freeze-dried [16].

Selection of conservation materials

Several resin and solvent mixtures were selected for evaluation as consolidants and adhesives for amber. It was decided to investigate materials with known consolidating properties, taking the approach that any added consolidants would be removed from small pieces of the conserved amber prior to analysis.

The properties considered important for a consolidant or adhesive for amber are good chemical and colour stability, easy reversibility, good adhesive properties, minimal interference with the infrared spectrum of amber, and minimal alteration of the visual appearance of amber. Although it is desirable that a consolidant be reversible, any attempt to remove a consolidant from a friable surface will lead to some loss of material; hence, removal of consolidant from a complete object would not usu- ally be attempted. For analysis it would only be necessary to remove the consolidant from a small sample. The materials investigated are shown in Table 1.

Paraloid B72 was chosen for evaluation since it has recently been used with considerable success to conserve amber at the British Museum. Paraloid B67 was also selected, because it is soluble in less polar solvents than Paraloid B72, the solubility of

Table 1 Materials investigated

Material Chemical type Film cast from

Paraloid B72 Ethyl Dimethylbenzene methacrylate

Paraloid B67 Butyl White spirit methacrylate

Synacryl 9122X Acrylic resin Dimethylbenzene, as supplied

Acrysol WS 50 Acrylic colloidal dispersion Water, as supplied

Primal WS 24 Acrylic colloidal dispersion Water, as supplied

Mowilith DMC2 Polyvinyl acetate emulsion Water, as supplied

amber being greater in polar solvents. Polar solvents such as alcohols and ethers dissolved up to 25% of the amber in solubility tests [5, 6]. This obviously ruled out solvents such as industrial methylated spirit (IMS). White spirit, butanone (methyl ethyl ketone) and dimethylbenzene have been evaluated for their effects on amber and proved to have a low solvent effect [5]. They were therefore selected for use in this evaluation. Paraloid B67 has not been widely used in conservation as it has been shown to be less flexible than Paraloid B72. However, amber is a brittle material and so flexibility is not a required property. Also it has been reported that butyl methacrylates such as B67 crosslink on light-aging to become less soluble [17]. However, this behaviour has not been observed in tests carried out at the British Museum. Synacryl 9122X was also tested, as good results have been reported [12].

Consolidants that might be suitable for the conservation of wet or waterlogged amber on archaeological excavations were also included in the evaluation. Mowilith DMC2 has been used in the treatment of waterlogged amber. Primal WS 24 and Acrysol WS 50, were selected because they have been recommended as consolidants for organic materials, such as waterlogged bone and glass [18-20].

The introduction of a material chemically similar to amber was thought to be inadvisable-for example, adding Baltic amber to non-Baltic amber would confuse analysis-and therefore 'oil of amber' was not included. Beck has suggested that only materials with no absorptions in the 1100-1250cm-1 region of the infrared, used for provenancing, should be employed to treat ambers [1]. Paraffin wax is such a material but was discounted in this study because of unsightly past repairs made using wax in the British Museum.

Evaluation of suitability for use with amber

Thin films of each of the chosen materials (listed in Table 1) were cast and aged by exposure to heat (70TC for 28 days) and light (Microscal MTL 4000 bulb for 28 days). The reflectance spectrum of the films was collected using a Perkin Elmer 551S UV/visible spectrophotometer and CIELAB co- ordinates were calculated to allow the colour differ- ence (AE) to be determined. Infrared spectra of the films were obtained by sampling onto silicon car- bide discs and using DRIFTS on a Nicolet 510 FTIR spectrometer. A thin film of each material, aged in contact with amber, was also evaluated to determine any synergistic effects. The solubility of the 'as cast' and heat-aged films in white spirit, butanone and dimethylbenzene was determined.





The solubility of the light-aged B67 was also determined. The results and rankings for interference of the infrared spectrum of a material with that of Baltic amber are shown in Table 2.

As expected, the Paraloids exhibited good stability and reversibility. Mowilith DMC2 and Synacryl 9122X yellowed on aging, and changes in the infrared spectra indicated that chemical changes had occurred. Further investigation of these materials was therefore abandoned. Acrysol WS 50 and Primal WS 24 showed reasonable stability (some changes in infrared spectrum) and reversibility and may be suitable for consolidation of wet or waterlogged amber, where their water base would be an advantage. They were not tested further, as no such amber was available.

The removal of Paraloid B72 and B67 from amber was assessed as follows. Pieces of Baltic

amber were soaked for eight hours in a 5% w/v solution of Paraloid B72 in dimethylbenzene or 5% w/v B67 in white spirit. They were then allowed to dry under ambient conditions for seven days. Removal of the B72 from the consolidated amber was attempted by soaking the sample in dimethylbenzene for 16 hours and allowing it to dry. The piece consolidated with B67 was similarly treated by soaking with white spirit. Infrared spectra of the amber pieces before consolidation, after consolidation and after soaking were collected using a dia- mond cell accessory. Spectra for B72 are shown in Figures 3, 4 and 5. The additional weak absorptions due to Paraloid B72 can just be seen in the spectrum of amber after consolidation (Figure 4). No significant differences were observed between the spectra obtained before consolidation (Figure 3) and after removal (Figure 5). Similar results were

Table 2 Results of testing of materials

Material Aging CIE Alterations to infrared Reversibility (%) Interference regime colour spectrum with infrared

differ- White Butanone Dimethyl- spectrum of ence spirit benzene Baltic amber

Paraloid B72 light 2-22 none N N N dark 1-17 none 0 97 97 on amber 7-93 N N N N

Paraloid B67 light 1-31 none 99 97 98 II dark 2-46 none 94 99 98 on amber 5.97 N N N N

Synacryl 9122X light 2-35 reduced intensity of N N N V bands at 1015, 960, 940, 850, 800cm-1

dark 5-94 ditto 50 58 95 on amber 4-29 N N N N

Acrysol WS 50 light 1.59 total loss of bands at N N N III 3400 and 1550cm-'

dark 1-29 total loss of band at 1 94 76 1550cm-'

on amber 3.71 N N N N

Primal WS 24 light 2-24 reduced intensity of band N N N IV at 1550cm-'

dark 0.81 none 0 98 2 on amber 7.55 N N N N

Mowilith DMC2 light 5.51 increase in intensity of N N N VI band at 3420cm-'

dark 9-39 total loss of band at 0 70 48 3420cm-'

on amber 4-28 N N N N

Baltic amber dark 6.42 N 1 5 9

N = not tested. Interference ranking: I = least, VI = most.





1-448 1404 exocyclic methylene

1-20 Region used to Provenance European ambers

1.00 U

S0.80

< 0o.60

040 0.201

0.096

2000 1767 1533 1300 1067 833 600 WAVENUMBERS

Figure 3 Infrared spectrum of amber before consolidation.

0403

3 B72 absorption

0.35

0.30-

u 0.25 U

S0.20 < 0o15 consolidated

o 0.10 , amber

- 5B72 0.009 I 1 i

2000 1767 1533 1300 1067 833 600 WAVENUMBERS

Figure 4 Infrared spectrum of amber after consolidation with Paraloid B72.

0421

0.40

0'35-

S030 U

O 025-

020-

0"15

0.10-

00711---- - 2000 1767 1533 1300 1067 833 600

WAVENUMBERS

Figure 5 Infrared spectrum of amber after removal of B72 with dimethylbenzene.

obtained for B67. This indicates that treatment will not adversely influence future infrared analysis for either identification or provenance studies, provided that records of treatment are accessible and removal of consolidants is undertaken.

Tests of adhesive properties The following were prepared as both 10% w/v and 20% w/v solutions: Paraloid B67 in white spirit, in petroleum spirit (boiling point range 100-140?C) and in butanone; Paraloid B72 in butanone and in dimethylbenzene.

The 10% Paraloid solutions were tested for use as consolidants. Since no friable amber was available for testing, small amber chips were crushed. The chips were sprinkled onto the surface of a piece of amber and the solutions were applied by pipette. The 20% Paraloid solutions were tested as adhesives. Several large pieces of amber were adhered together using the solutions applied with a fine sable brush. The strength of the test pieces was assessed empirically. The strength of all of the test pieces was considered acceptable.

Suitable materials

Paraloid B72 and B67 are both suitable as consolidants or adhesives for amber, and can be used in a number of solvents (see Table 2). Paraloid B67 has the advantage of being soluble in white spirit, the least polar of the solvents tested, but solutions were difficult to prepare at high concentrations. The final choice of consolidant/adhesive and solvent is best dictated by the degree of degradation of the particular object to be treated.

Case studies

A recent survey of amber artifacts in the Department of Greek and Roman Antiquities at the British Museum revealed the need for conservation treatment of some objects that were broken or very fragile. Improvement in the storage conditions was thought to give sufficient protection in the majority of cases. In a few cases the amber was so friable that interventive treatment was considered essential. Two cases where the application of consolidants and adhesives was necessary are described below.

Etruscan necklace of silver pendants and amber beads

Prior to treatment, the amber beads on this necklace (Registration No. G&R 72,6-4.1004) were in a deteriorated condition, with very powdery and friable surfaces (Figure 6). There was evidence of damage caused by abrasion between the silver pendants and the amber beads. Wax had been used in the past to repair and fill gaps in the amber. It was decided to leave these old repairs: although they were unsightly, they were not causing any damage.





Figure 6 Necklace (Registration No. G&R 72,6- 4.1004) before treatment.

The positioning of the beads was carefully noted before removal of the modern thread that had been used for stringing. The amber beads were then successfully consolidated with a 5% w/v solution of Paraloid B67 in white spirit applied by pipette. A 5% solution was chosen because it had been found to have suitable working properties. After drying, the surface of the most degraded beads was still friable and so a second coat was applied to these beads, in the same manner. The treatment proved successful, securing the surface whilst leaving the amber visually unchanged (Figure 7).

In order to minimize any future abrasion between the amber and the silver, and within the holes of the amber beads, the necklace was restrung on a new linen thread covered with polyolefin tubing. Small circles of 2mm-thick black Plastazote (poly- ethene) foam were cut and inserted over the tubing between each bead and pendant to provide some protective padding. The black colour of the foam was not too obtrusive between the dark amber beads and the dark patinated colour of the silver. The polyolefin tubing helped to shape the necklace into a gentle curve, thus preventing the beads from knocking against one another (Figure 8).

For additional support in storage, the necklace was laid into 20mm-thick white Plastazote foam

Figure 7 The necklace in Figure 6, after treatment.

with depressions cut to fit the contours of the beads. A Correx (polypropylene) tray was made to enclose the Plastazote mount and provide rigidity so that the necklace could be moved safely. The necklace is now readily available for study with minimal handling.

Etruscan necklace of faceted triangular amber pendants separated by small gold beads

The amber was in a degraded condition, with several missing sections. Many of the amber tubes through which the necklace (Registration No. G&R 72,6-4.719) was strung were badly damaged, leaving jagged edges vulnerable to abrasion between adjacent beads (Figure 9). The loss of parts of the amber tubes also meant that the amber pendants were likely to abrade one another, due to their close proximity. There were two loose amber pieces which needed rejoining to two of the amber pendants. Past repairs were evident but were not ana- lyzed and were left in situ.

After removal of the cord, the amber was consolidated with a 5% w/v solution of Paraloid B67 in





C Crn i Figure 8 Detail of the necklace in Figure 7, showing Plastazote spacers and polyolefin tubing.

petroleum spirit, applied by pipette. A second coat was applied to the most degraded pendants. Petroleum spirit was chosen instead of white spirit in this case because it evaporates more rapidly, facilitating the making of joins. B67 is also quicker and easier to prepare in petroleum spirit in the higher concentration required for an adhesive. The two loose pieces were rejoined to the necklace with a 20% solution of B67, using a fine sable brush.

Figure 9 Necklace (Registration No. G&R 72,6- 4.719) before treatment.

Due to the very narrow holes in the gold beads, only a double cotton thread could be used for restringing. Since the necklace was much lighter in weight than the previous example, there was less need for the extra support provided by the polyolefin tubing. However, the vulnerable broken sections of the amber tubes were protected by inserting small lengths of polyolefin tubing, secured with small spots of B67 adhesive, to extend the amber tubes to their original length. This also spread out the amber beads so that they are less likely to abrade one another. Small circles of 100lm-thick Melinex (polyester) sheet were cut with a paper hole-punch and threaded between each gold bead and amber pendant, to minimize abrasion (Figure 10).

Figure 10 Detail of the necklace in Figure 9, after treatment, showing Melinex spacers and polyolefin tubing.

A mount was made from two layers of 10mm- thick white Plastazote foam. The upper layer was cut right through, to the shape of the necklace, before securing the layers together with polyvinyl acetate emulsion. The necklace could then be safely laid into the mount for storage. A Correx tray was made as described in the previous example (Figure 11).

Display and storage recommendations

Amber is brittle and can be fragile when deteriorated. Therefore care should be taken to minimize handling, for example by the provision of foam supports and suitable stringing for necklaces in storage and of sufficient support for display.

There have been no long-term studies of the stability of amber under different environmental conditions. Work has been reported on the oxidation rate of freshly exposed amber surfaces under vari- ous conditions [21]. This indicated that relative





Figure 11 The necklace shown in Figure 9, sup- ported in Plastazote foam cut-out and Correx tray.

humidity should be kept above 40%, but that high levels of humidity accelerate the oxidation of amber. Therefore amber should be maintained at the conditions generally recommended for susceptible organic artifacts (45-55% RH). Extremes of temperature should be avoided and 17-25"C is an appropriate range. Visible light is reported not to affect amber but ultraviolet light can cause rapid degradation. UV can generally be totally excluded during storage and UV-filtering films can achieve levels of 50gtW per lumen for display.

It should be noted that deteriorated amber may react differently from a freshly exposed amber surface. Since amber degrades by atmospheric oxidation, an oxygen-free environment might be expected to reduce deterioration.

Conclusion

Beck's advice to avoid consolidation unless it is necessary and to provenance amber before any consolidation, or to keep an uncontaminated sample for later study, is very sound [1]. Safe storage and display methods may provide sufficient protection, negating the need for interventive conservation, and these should be considered first. However, in some cases the amber is so deteriorated and fragile that treatment may be unavoidable. Many other materials are misattributed as amber and may have differ- ing susceptibilities to solvents. Therefore an unobtrusive area of the artifact should be tested with solvents first.

Paraloid B67 (in white spirit or petroleum spirit, boiling point 100-140"C) and B72 (in butanone or dimethylbenzene) were both found to be suitable as adhesives and consolidants for amber. Should it be necessary to analyze a piece of amber after consolidation with either of these resins, it was found that

the consolidant could be removed successfully from the small sample needed for analysis, by using dimethylbenzene or white spirit, as appropriate. These treatments have been used successfully on a number of amber artifacts from the Department of Greek and Roman Antiquities of the British Museum.

Tests showed that Acrysol WS 50 and Primal WS 24 had potential for the treatment of wet or waterlogged amber on archaeological excavations. It is intended to investigate the use of these materials further when suitable excavated amber becomes available.

Acknowledgements

Many people have given help and advice with this project. In particular the authors would like to thank Curt Beck (USA) and Knut Botfeldt (Denmark) for sharing their experience on amber and its conservation. We should also like to thank Paul Barford in Poland, David Thomsen, National Museum of Scotland, and the company Goldmajor Ltd, London, for supplying amber samples. Thanks are due to Elsbieta Nosek and Maria Dyrka for help during a study tour to Poland. We are also grateful to Allyson Rae (Organic Materials Conservation Section), Susan Bradley and Vincent Daniels (Conservation Research Section), for their help and support, and Andrew Oddy, Keeper of Conservation, for his encouragement.

Health and safety

White spirit is harmful by ingestion or inhalation of vapour. It is irritating to the skin and eyes. It has a UK occupational exposure standard (OES) of

-3 575mgm-3. Petroleum spirit (boiling range 100-140"C) is

harmful by ingestion, skin contact and vapour inhalation. It is extremely irritating to the eyes and has a UK OES of 1450mgm-3.

Butanone (methyl ethyl ketone) is harmful by ingestion and inhalation of vapour. It is irritating and may cause severe damage to the eyes. It has a UK OES of 580mgm-3.

Dimethylbenzene (xylene) is irritating to the skin and eyes and may be absorbed through the skin. The vapour is narcotic in high concentrations and it has a UK OES of 435mgm-3.

Acrysol WS 50 and Primal WS 24 both contain ammonia which is regulated under the UK COSHH (Control of Substances Hazardous to Health) regu- lations. Acrysol WS 50 also contains methanal (formaldehyde) which is a respiratory sensitizer.





For further information consult manufacturers' health and safety information.

Suppliers

Paraloid B72 (solid grade), Paraloid B67 (solid grade), Acrysol WS 50, Primal WS 24: Rohm and Haas (UK) Ltd, Lennig House, 2 Mason's Avenue, Croydon CR9 3NB, UK.

Synacryl 9122X: Cray Valley Ltd, Waterloo Works, Machen, Newport, Gwent NP1 8YN, UK.

Mowilith DMC2: discontinued. Dimethylbenzene (xylene), white spirit, butanone

(methyl ethyl ketone): Merck (BDH) Chemicals Ltd, Broom Road, Poole, Dorset BH12 4NN, UK.

Petroleum spirit, BP 100-140?C: Hayes Chemicals, King Street, Garston, Liverpool L19 8EG, UK.

Plastazote foam: Zote Foams Ltd, 675 Mitchum Road, Croydon, Surrey CR9 3AL, UK.

Polyolefin tubing: Shrink Tubes and Plastics Ltd, 25 Trowers Way, Redhill, Surrey RH1 2LH, UK.

Melinex sheet: Hi-fi Industrial Films Ltd, Gunnells Wood Industrial Estate, 3 Babbage Road, Stevenage, Herts SG1 2EQ, UK.

Correx: Correx Plastics, Madleaze Industrial Estate, Bristol Road, Gloucester GL1 5SG, UK.

Threads/cords: Janet Coles Beads Ltd, Perdiswell Cottage, Bilford Road, Worcester WR3 8QA, UK; The Bead Shop, 16 Redbridge Enterprise Centre, Thompson Close, Ilford, Essex IGI ITY, UK.

References

1 BECK, C. W., 'Authentication and conservation of amber: conflict of interests' in Science and Technology in the Service of Conservation, IIC, London (1982) 104-107.

2 CRONYN, J. M., The Elements of Archaelogical Conservation, Routledge, London (1990) 293.

3 BECK, C. J., and SHENNAN, S., Amber in Prehistoric Britain, Oxbow Monograph 8, Oxbow Books, Oxford (1991).

4 STRONG, D. E., Catalogue of the Carved Amber in the Department of Greek and Roman Antiquities, The Trustees of the British Museum, London (1966).

5 THICKETT, D., 'The influence of solvents on amber' in Conservation Science in the UK, ed. N. H. TENNENT, James and James Science Publishers Ltd, London (1993) 49-56.

6 BECK, C. W., 'Spectroscopic investigations of amber', Applied Spectroscopy Reviews 22 (1986) 58-109.

7 SHEDRINSKY, A. M., GRIMALDI, D., WAMPLER, T. P., and BAER, N. S., 'Amber and copal: pyrolysis gas chromatographic (PyGC) studies of provenance', Wiener Berichte ziber Naturwissenschaft in der Kunst 6/7/8 (1989/90/91) 37-63.

8 PREUSSER, F., 'Zur Restaurieung von Stark Korrodiertern Bernstein', Arbeitsbldtter far Restauratoren 2 (1976) 75-77.

9 FRAQUET, H., Amber, Butterworths Gem Books, Butterworths, London (1987) 58.

10 KUNKULIENE, B., LUKSENIENE, J., and VAITKUS, J., 'Application of vacuum device for archaeological amber conservation' in ICOM Committee for Conservation 6th Triennial Meeting, Ottawa (1981) 81/21/5:1-4.

11 THICKETT, D., 'Analysis of six adhesives and consolidants from Greek and Roman amber objects', British Museum Conservation Research Section Internal Report CA1992/50 (1992).

12 BOTFELDT, K., Ray, Konservatorskolen, Det Kongelige Danske Kunstakademi, Copen- hagen (1987).

13 RICE, P. C., Amber, The Golden Gem of the Ages, Van Nostrand Reinhold, New York (1980).

14 WATKINS, S., and CAMERON, E., 'An Iron Age warrior's grave from Guernsey: the excavation, conservation and interpret- ation of its contents' in Recent Advances in the Conservation and Analysis of Artifacts, Summer Schools Press, London (1987) 51-59.

15 PAYTON, R., 'The conservation of artefacts from one of the world's oldest shipwrecks, the Ulu Burun, Ka5 shipwreck, Turkey' in Recent Advances in the Conservation and Analysis of Artifacts, Summer Schools Press, London (1987) 41-51.

16 BROOKS, M., Conservation Centre, Salisbury, personal communication.

17 FELLER, R. L., 'Studies on the photochemical stability of thermoplastic resins' in ICOM Committee for Conservation 4th Triennial Meeting, Venice (1975) 75/22/4:1-10.

18 KOOB, S. B., 'Consolidation with acrylic colloidal dispersions' in Preprints, AIC 9th Annual Meeting, Philadelphia (1981) 86-94.

d19 KOOB, S. B., 'Recovery and treatment of skeletal remains at Herculaneum' in Retrieval of Objects from Archaeological Sites, ed. R. PAYTON, Archetype Publications, London (1992).





20 ROBERTS, J. D., 'Acrylic colloidal dispersions as pre-consolidants for waterlogged archaeological glass' in ICOM Committee for Conservation 7th Triennial Meeting, Copenhagen (1984) 84.20.21-22.

21 SCOTT WILLIAMS, R., WADDINGTON, J. B., and FENN, J., 'Infrared spectroscopic analysis of Central and South American amber exposed to air pollutants, biocides, light and moisture', Collection Forum 6 (1990) 65-75.

Authors

DAVID THICKETT gained an honours degree in natural sciences from Cambridge University in 1988. He worked for two years carrying out research in the ceramics industry and joined the Conservation Research Section of the Department of Conservation of the British Museum in 1990. Current research interests include the conservation of stone and methods for reducing the impact of materials used in the storage and display of antiqui-

ties. Address: Department of Conservation, British Museum, London WC1B 3DG, UK.

PIPPA CRUICKSHANK joined the Department of Conservation at the British Museum in 1977, gain- ing the Museums Association Conservation Certificate in 1985. She is a senior conservator in the Organic Materials Section, specializing in the conservation of textiles. Her research into amber and its conservation was carried out in preparation for a study tour to Poland in 1991, where she looked into the conservation of amber and other organic materials. Address: as for Thickett.

CLARE WARD gained a BSc(Hons) in archaeological conservation from the Institute of Archaeology, University of London, in 1981. After short-term conservation contracts in the UK and Denmark, she joined the Department of Conservation at the British Museum in 1982. She is a senior conservator in the Organic Materials Section, specializing in the conservation of archaeological organics, such as skeletal materials, wood and amber, and also modern plastics. Address: as for Thickett.

R6sum6-Le British Museum de Londres possede d'importantes collections d'objets en ambre, sur lesquels on effectue des analyses, d la fois pour authentifier l'ambre et connaftre sa provenance. On a largement employe dans le passe la spectroscopie infrarouge, mais d'autres miethodes sont maintenant disponibles. Plusieurs fac- teurs, dont les conditions environnementales, participent d la ddtirioration de l'ambre, le rendant fragile d la manipulation. Quand la consolidation est ndcessaire, les matiriaux employes ne doivent pas gener une future analyse possible. Ce papier indique une selection de melanges de risine et de solvent pour la consolidation de l'ambre, ainsi que des miethodes sares de stockage et d'expositions. Les matiriaux recommandis ont des pro- prietts bien connues et peuvent etre enlevis des petits echantillons avant l'analyse.

Zusammenfassung-Das British Museum in London besitzt umfangreiche Sammlungsbestdnde an Bernsteinobjekten. Die vorliegende Arbeit berichtet fiber die Analyse solcher Objekte zur Kldrung der Materialfrage und ihrer Herkunft. Als Untersuchungsmethode war in der Vergangenheit die Infrarotspektroskopie weit verbreitet, bis andere Methoden verfiigbar wurden. Verschiedene Faktoren wie etwa die Umgebungsbedingungen tragen zur Zerstirung von Bernstein bei, indem sie seine Empfindlichkeit gegen Beschddigung durch Beraihrung erhdhen. Sofern Konsolidierungsmafjnahmen notwendig werden, diirfen die hierzu verwendeten Materialien m6gliche spdtere Untersuchungen nicht behindern. Die Autoren diskutieren die fiur diesen Zweck ausgewdhlten Harze und Lisungsmittelmischungen und schlagen verbesserte Methoden fir Lagerung und Prdsentation vor. Die Eigenschaften dieser Materialien sind bekannt und vor einer Untersuchung ist es miglich, sie von den Proben zu entfernen.

Resumen--El British Museum de Londres tiene extensas colecciones de objetos de dambar. Se lleva a cabo un analisis del dmbar tanto para establecer tanto su autenticidad como su procedencia. En el pasado se ha uti- lizado generalmente la espectroscopia infrarroja, pero estdn surgiendo otros mitodos. Varios factores, incluyendo las condiciones medioambientales, contribuyen al deterioro del dambar, dejdndolo vulnerable a dafios causados por la manipulaci6n. Donde se requiere la consolidaci6n, los materiales utilizados no deben interferer en los posibles analisis futuros. Este informe trata la seleccidn de mezclas de resinas y disolventes para la con- solidacidn del dmbar, ademds de los metodos mejorados para el almacenamiento y la exposicidn. Los materiales recomendados tienen propiedades bien conocidas y se pueden eliminar de pequenfas muestras antes de analizarlas.


