Figure 1
FTIR Results for Baltic Amber and Amber Object 76.AO.84
Figure 2
THM-Py-GC/MS Results for Baltic and Dominican Ambers
Figure 3
THM-Py-GC/MS Results for Core Sample from Amber Object 82.AC.161.285
Figure 4
Variation in FTIR Spectrum with Succinate Content for Amber Objects (Core Samples)
Figure 5
THM-Py-GC/MS Results for Dark Surface and Inner Core of Amber from Verfmolen 'De Kat'
Figure 6
THM-Py-GC/MS Results for Surface and Inner Core Samples from 83.AO.202.1
Figure 7
FTIR Spectra for Surface and Core Samples from 83.AO.202.1
Figure 8
FTIR Spectra for Surface and Core Samples from 82.AO.161.7
Figure 9
THM-Py-GC/MS Results for Surface Samples from Treated Amber Objects
Figure 10
FTIR Results for Core Samples from Treated Amber Objects
©J. Paul Getty Trust

By Jeff Maish, Herant Khanjian, and Michael Schilling.
"Analysis of Selected Ambers from the Collections of the J. Paul Getty Museum", Ancient Carved Ambers in the J. Paul Getty Museum.
Ed. Faya Causey. Los Angeles: Getty P, 2012. museumcatalogues.getty.edu. Web. 15 December 2018.
<http://museumcatalogues.getty.edu/amber/essay/>

Technical Essay

Analysis of Selected Ambers from the Collections of the J. Paul Getty Museum

By Jeff Maish, Herant Khanjian, and Michael Schilling

Introduction

Amber has been appreciated since antiquity for its unique aesthetic qualities in the production of small decorative objects. It has been a source of both mystery and curiosity, as it bridges the divide between the living and organic and the mineral and inorganic. It was initially selected for qualities such as color and hardness, with an eye toward an end market in jewelry production, and the Baltic Sea coastline has, and continues to be, the largest source of the material.

The focus of amber studies over the past two hundred years has paralleled scientific developments in instrumentation and methods. Some of the earliest investigators used microscopy to view a hidden world of natural history and provide insights into past geological ages. More recent studies have analyzed the material itself in an attempt to better understand its chemistry, origins, and deterioration processes. This has included the identification of imitation ambers composed of natural and man-made compounds.[1]

Amber Characteristics

Although amber types have been classified generally, some ambiguities remain. Visual characteristics of amber such as color and translucency do not clearly relate to differences in chemical composition, [2] and some differences may relate more closely to inclusions, entrapment of air, and states of oxidation. Amber may also be defined by grade, color, or even by geographic origin, such as Romanian or Sicilian. Ambers such as Baltic may be further subdivided into the categories allingite, beckerite, gedanite, or glessite, based in part on opacity, color, and friability.[3] Some subdivisions are also morphological. For example, amber with many tiny bubbles may be termed “bone” amber, whereas “foamy” amber has slightly larger bubbles. Amber typing can, therefore, be viewed from different perspectives ranging from morphological to chemical.

Amber Deterioration and Conservation

Although amber may have lain relatively dormant in geological deposits for thousands of years, its relatively recent collection, shaping, use, and reburial has often resulted in continued—and in some instances severe—deterioration. In general, deterioration manifests itself as a thick “corrosion” crust that not only obscures the translucent quality of amber but may also lead to flaking and loss of the carved surface. In the worst-case scenarios, the carved surface completely flakes off, leaving an ambiguously shaped amber core. Deterioration may continue in a collections environment and be aggravated by pollutants, oxidation processes, and inappropriate environmental controls.[4] Recently, the degradation mechanisms and conservation treatments of archaeological amber have been studied using a variety of analytical instrumentation.[5]

Over the years, restorers and, more recently, conservators have attempted to reinforce fragile amber surfaces by applying a range of consolidative organic materials. Examples of past amber consolidants include dammar resin and “amber oil,” a product of amber distillation.[6] A variety of waxes and natural and synthetic resins have also been applied. While preserving the morphological characteristics of carved amber, organic consolidants may interfere with future attempts to analyze or classify the amber. Therefore, the consolidation process should be carefully considered and, if carried out, fully documented.[7]

Scientific Analysis of Amber

The study of amber has kept pace over the last two centuries with the developments in scientific analysis. Microscopic studies beginning in the eighteenth century focused on the morphological characteristics of amber and the recognition of amber’s botanical origins.[8] As methods for chemical analysis developed, so did the understanding of amber’s complex chemical structure.[9] Considering the archaeological context of many amber finds, its characterization is further complicated by material degradation and possible interference from a past stabilization treatment.[10] Beginning in the 1960s, analytical studies of amber relied heavily on infrared spectroscopy (IR)[11] and nuclear magnetic resonance (NMR).[12]

IR spectroscopy, in particular, was the first technique capable of readily identifying Baltic amber through the presence of a distinct succinic acid peak or “shoulder” in its infrared spectrum. However, the limits of this method were reached when it proved less successful in distinguishing between non-Baltic ambers. More recent analytical studies have employed Raman spectroscopy, [13] capillary gas chromatography/mass spectrometry (GC/MS), [14] and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), [15] which are capable of isolating a broad range of compounds that compose amber.[16] Combined with other analysis, this has led to proposals for the botanical origins of some ambers as well as common sourcing for previously distinct ambers.[17]

Current Research

The primary goal of the scientific investigation of a group of amber objects from the collections of the J. Paul Getty Museum was to verify that the ambers were indeed of Baltic origin. A secondary aim was to ascertain whether treatment with amber oil or other organic materials might interfere with the identification process. Samples were removed from the cores of 26 amber objects for analysis at the Getty Conservation Institute using Fourier-transform infrared spectroscopy (FTIR) and pyrolysis-gas chromatography/mass spectrometry with tetramethyl ammonium hydroxide (THM-Py-GC/MS). In addition to the core samples, surface samples were also removed from seven amber objects in order to better understand the composition of weathered amber surfaces. For comparative purposes, tests were carried out on a number of reference materials, including Baltic amber, Dominican amber, copal resin, pine resin, sandarac resin, dried residue from amber oil distillate, and amber varnish.

Fourier-Transform Infrared Spectrometry Procedure

The samples were analyzed on a Nic-plan infrared microscope equipped with a nitrogen cooled MCT/A detector. Selected amber particles were placed on an infrared diamond window, flattened with a metal roller and analyzed using a transmitted infrared beam apertured to 100 x 100 microns. The spectra are the sum of 100 scans at a resolution of 4 cm-1. Infrared analysis of the samples produced spectra containing bands that correspond to amber. For example, a characteristic peak attributed to the carbon-oxygen bond at 1158 cm-1 distinguishes Baltic amber. Additional bands at 1737 and 1715 cm-1 are assigned to the ester and carboxylic acid groups, whereas peaks located at 1643 and 888 cm-1 are attributed to the exocyclic methylene group. Other components may be present in the samples at concentrations below the detection limit (5%).

THM-Pyrolysis-Gas Chromatography/ Mass Spectrometry Procedure

Samples were tested on an HP 5972 gas chromatograph/mass spectrometer using a CDS Pyroprobe 2000, fitted with a valved interface at 330°C and purged with helium at 25 ml/minute. The split injector was at 340°C (30:1 ratio), and the MS transfer line was set to 300°C. A DB-5MS capillary column (30 M x 0.25 mm x 0.25 µm) was used with helium at 44cm/sec. The GC oven temperature program was 2 minutes at 40°C, then 6°C/minute to 310°C, and 13-minute isothermal. The solvent delay was 2.5 minutes. The mass spectrometer was scanned from m/z 35–700. Samples were placed into quartz tubes fitted with quartz wool, and three microliters of 25% tetramethyl ammonium hydroxide (TMAH) in methanol were introduced for derivatization. After three minutes, the tube was placed into a coiled filament probe, which was inserted into the valved interface. After purging for three seconds before pyrolysis, samples were pyrolyzed using the following temperature program: 200°C for 1 second, then ramped at 10°C/millisecond to 700°C, and held isothermally for 10 seconds.

Figure 1, an overlay of the FTIR spectra for Baltic amber and an amber object (76.AO.84), reveals characteristic spectral differences that make it possible to positively identify Baltic amber. The infrared spectrum of Baltic amber shows characteristic intense absorption bands at 2926, 2867, and 2849 cm-1 attributed to C-H stretching modes of the CH2 and CH3 groups. A doublet for carbonyl C=O stretching peaks at 1739 and 1714 cm-1 is characteristic of ester and acid groups. Additional bands at 1260 and 1157 cm-1 are assigned to CO-O- modes of the succinate group, whereas the C-H bending modes for the terminal olefins are located at 888 cm-1. Finally, peaks located at 1643 and 888 cm-1 are attributed to the exocyclic methylene group.

In THM-Py-GC/MS results for Baltic and Dominican amber standards (figure 2), a total of 69 compounds were identified. Many of these are sesquiterpene and diterpene compounds that are abundant, though not especially characteristic of the type of amber, as well as numerous nonspecific compounds. Succinic acid is the dominant marker compound for Baltic amber, and it appears in the chromatogram as a large peak at 10.3 minutes. In this study, succinic acid was analyzed in the form of the dimethyl ester derivative, and is abbreviated in figures as succinate. In figure 3, which shows THM-Py-GC/MS results for amber object 82.AC.161.285, other Baltic amber marker compounds are present in varying amounts, including fenchol, borneol, camphene, and camphor. Two very small peaks identified as methyl fenchyl succinate and methyl bornyl succinate (Mills et al. 1984) may also appear in THM-Py-GC/MS results for Baltic ambers.

Tables 1, 2, 3, and 4 list the various classes of compounds identified in the THM-Py-GC/MS analysis results of the amber objects and the reference materials. The identifications were based primarily on the results from mass spectral library searching using the NIST MS Search 2.0 program, and supplemented by published data (Mills et al. 1984). Although the NIST results of the nonspecific compounds listed in table 5 were inconclusive, the unknown compounds did appear on a rather consistent basis in the objects.

The THM-Py-GC/MS results for the reference samples appear in table 6. In this and all subsequent tables, the test results are expressed in terms of peak-area percentages relative to the total peak area for all of the compounds listed in tables 1, 2, 3, 4, and 5 (except for methyl fenchyl succinate, methyl bornyl succinate, and dibornyl succinate, which, due to their extremely small peak sizes, did not contribute significantly to the total peak area). Table 6 shows that the succinate content in the single known sample of Baltic amber was high, whereas almost no succinate was detected in the Dominican ambers, copal resin, sandarac resin, or pine resin. The succinate content in the ambers of unknown origin appeared rather variable, but the presence of the other markers in table 1 placed them firmly in the Baltic category. The “amber varnish” was found to contain a high concentration of a drying oil with no detectable succinate content. Fortunately, the test results for dried amber oil residue showed no significant amounts of any of the Baltic marker compounds listed in table 1 except for borneol, indicating that amber oil treatment should not produce a “false positive” identification for Baltic amber.

In the THM-Py-GC/MS results for the core samples from the untreated amber objects (table 7), the most striking feature is the remarkably broad range for the succinate content compared to the composition of the standards. In an overlay of FTIR spectra for some of these samples (figure 4), the main trend is the shift of the carbonyl peak to lower wavenumber with increasing succinate content, which is characteristic of the conversion of esters to carboxylic acids. These results provide evidence that partial hydrolysis of the succinate esters in the objects has occurred, which is a reaction that would enrich the residual amber in succinic acid.

One concern in this study was that the composition of the surface crusts of the amber objects might be considerably different from that of the inner cores due to hydrolysis, weathering, handling, and treatment. This is why core samples were removed from the objects by microdrilling. In figure 5, the THM-Py-GC/MS results for the dark surface and inner core of a large piece of reference amber, it is clear that the surface has become partially depleted in succinate, with little other changes apparent. Table 8 shows the results for pairs of surface and core samples for the amber objects, and figure 6 shows a typical chromatographic result (83.AO.202.1). The surfaces of these objects have also been depleted in succinate, but the sesquiterpenes and diterpenes also have been radically reduced. These compounds are not chemically bound to the polymeric network of the amber, which would make them more susceptible to leaching during burial.

FTIR analysis also reveals important details about the nature of the surface and core compositions. Figure 7 shows FTIR spectra for surface and core samples from 83.AO.202.1. The saturated C-H bands at 2927 and 2869 cm-1 in the spectrum of the surface sample are reduced, whereas the C-O stretching modes at 1159 cm-1 in the fingerprint region are more intense. This indicates the surface is more highly oxidized than the core. The other important peak appears at 1574 cm-1, which is due to salts of succinic acid. There is a much higher concentration of succinate salts in the surface sample, which is consistent with exposure to alkaline conditions during some period of time.[18] This might have occurred during burial, or from harsh cleaning with alkaline chemicals. FTIR spectra of two surface samples and the core from 82.AO.161.7 (figure 8) show the increased O-H stretching band in the surface sample, with a shift in the C=O band to lower wavenumbers, indicating the prevalence of carboxylic acids. However, the succinate salt peak at 1574 cm-1 is only a slight shoulder on the carbonyl peak, indicating that this object was not exposed to the same harsh alkaline conditions of 83.AO.202.1.

Table 9 lists the THM-Py-GC/MS results for the treated amber objects, and representative chromatograms are shown in figure 9. Azelaic acid was detected in three of the objects (77.AO.81.29, 77.AO.81.5, and the surface of 77.AO.81.30; cat. nos. 16, 23, and 25). This is a common marker compound for cross-linked drying oils, and its presence along with palmitic acid and stearic acid indicates that drying oils may have been applied to these objects in an alternative type of conservation treatment. In 77.AO.81.4, palmitic and stearic acids were detected along with cholesterol, but azelaic acid is absent. This suggests that an animal fat could have been applied to this object as another type of alternative treatment. Three amber objects tested in this study had been previously treated with amber oil: 77.AO.84, 77.AO.83, and 77.AO.81.7; catalogue numbers 1, 38, and 41. Their extremely high succinate contents suggest that they were highly degraded prior to treatment. In figure 10, the FTIR spectra for selected treated samples show that treatment with drying oil or amber oil does not interfere with the identification of Baltic amber.

Conclusions

This study has demonstrated that chemical analysis using FTIR and THM-Py-GC/MS can provide rich details concerning the composition of antique amber objects. Fundamentally, the analytical results showed that all of the amber objects in the J. Paul Getty Museum are classified as Baltic amber. Additional information revealed the nature and extent of deterioration, and provided tantalizing hints about the nature of the burial conditions to which some of these objects may have been exposed. Finally, detection of certain marker compounds has shown that a number of amber objects were treated with drying oils and fats and, furthermore, that amber oil treatment does not interfere with the provenancing process.




Tables

Table 1: Marker Compounds from THM-Py-GC/MS Analysis of Amber Objects
IUPAC Name Synonym CAS # Formula MW Retention Time, min
Bicyclo[2.2.1]heptane, 2,2-dimethyl-3-methylene- Camphene 79-92-5 C10H16 136 8.04
Butanedioic acid, dimethyl ester Succinic acid, dimethyl ester 106-65-0 C6H10O4 146 10.27
Bicyclo[2.2.1]heptane, 2-methoxy-1,3,3-trimethyl- Methyl fenchyl ether N/A C11H20O 168 12.35
Bicyclo[2.2.1]heptan-2-ol, 1,3,3-trimethyl- Fenchyl alcohol 1632-73-1 C10H18O 154 12.50
Bicyclo[2.2.1]heptan-2-one, 1,7,7-trimethyl-, (1S)- L-camphor 464-48-2 C10H16O 152 13.20
Bicyclo[2.2.1]heptan-2-methoxy, 1,7,7-trimethyl-, (1S-endo)- Methyl bornyl ether N/A C11H20O 168 13.48
Bicyclo[2.2.1]heptan-2-ol, 1,7,7-trimethyl-, (1S-endo)- L-borneol 464-45-9 C10H18O 154 13.83
Naphthalene, 1,2,3,4-tetrahydro-1,8-dimethyl- 25419-33-4 C12H16 160 17.44
Cedren-13-methoxy, 8- N/A C16H26O 234 24.80
Methyl fenchyl succinate N/A C15H24O4 268 25.16
Methyl bornyl succinate N/A C15H24O4 268 26.54
Cedren-13-ol, 8- 18319-35-2 C15H24O 220 26.92
Dibornyl succinate N/A C24H38O4 390 38.64

Table 2: Diterpenes Identified in Amber Objects Using THM-Py-GC/MS Analysis
IUPAC Name Synonym CAS # Formula MW Retention Time, min
Podocarp-8-en-15-oic acid, 13alpha-methyl-13-vinyl-, methyl ester Methyl pimara-8,15-dien-18-oate 19907-21-2 C21H32O2 316 33.17
Podocarpa-8,11,13-trien-15-oic acid, 13-isopropyl-, methyl ester Methyl dehydroabietate 1235-74-1 C21H30O2 314 35.14
Methyl 5-(5,5,8a-trimethyl-2-methylenedecahydro-1-naphthalenyl)-3-methylpentanoate Labd-8(20)-en-15-oic acid, methyl ester 13008-80-5 C21H36O2 320 33.49
Methyl pimar-7-en-18-oate 72088-13-2 C21H34O2 318 33.80
Labda-8(20),12,14-trien-19-oic acid, methyl ester, (Z)- Methyl cis-Communate 10178-35-5 C21H32O2 316 33.95
Podocarp-8(14)-en-15-oic acid, 13á-methyl-13-vinyl-, methyl ester Methyl sandaracopimarate 1686-54-0 C21H32O2 316 33.95
Podocarp-7-en-15-oic acid, 13á-methyl-13-vinyl-, methyl ester Methyl isopimarate 1686-62-0 C21H32O2 316 34.61
Podocarpa-7,13-dien-15-oic acid, 13-isopropyl-, methyl ester Methyl abietate 127-25-3 C21H32O2 316 35.84
Podocarpa-6,8,11,13-tetraen-15-oic acid, 13-isopropyl-, methyl ester Methyl 6-dehydrodehydroabietate 18492-76-7 C21H28O2 312 36.43

Table 3: Fatty Acids in THM-Py-GC/MS Analysis of Lipids
IUPAC Name Synonym CAS # Formula MW Retention Time, min
Hexanedioic acid, dimethyl ester dimethyl adipate 627-93-0 C8H14O4 174 15.47
Heptanedioic acid, dimethyl ester dimethyl pimelate 1732-08-7 C9H16O4 188 17.78
Octanedioic acid, dimethyl ester dimethyl suberate 1732-09-8 C10H18O4 202 20.02
Dodecanoic acid, methyl ester methyl laurate 111-82-0 C13H26O2 214 21.63
Nonanedioic acid, dimethyl ester dimethyl azelate 1732-10-1 C11H20O4 216 22.10
Decanedioic acid, dimethyl ester dimethyl sebacate 106-79-6 C12H22O4 230 24.03
Tetradecanoic acid, methyl ester methyl myristate 124-10-7 C15H30O2 242 25.48
Hexadecanoic acid, methyl ester methyl palmitate 112-39-0 C17H34O2 270 28.96
9-Octadecenoic acid (Z)-, methyl ester methyl oleate 112-62-9 C19H36O2 296 31.71
Octadecanoic acid, methyl ester methyl stearate 112-61-8 C19H38O2 298 32.13
Eicosanoic acid, methyl ester methyl arachidate 1120-28-1 C21H42O2 326 35.01

Table 4: Nonspecific Compounds Identified in THM-Py-GC/MS Analysis of Amber Objects
IUPAC Name Synonym CAS # Formula MW Retention Time, min
Methyl benzene Toluene 108-88-3 C7H8 92 3.76
1,3-Dimethyl-1-cyclohexene 2808-76-6 C8H14 110 4.92
Benzene, 1,4-dimethyl- p-Xylene 106-42-3 C8H10 106 5.99
Benzene, 1,3-dimethyl- m-Xylene 108-38-3 C8H10 106 5.99
2-Propenoic acid, 2-methyl-, methyl ester Methyl methacrylate 80-62-6 C5H8O2 100 2.87
Ethylbenzene 100-41-4 C8H10 106 5.77
Benzene, 1,2-dimethyl- o-Xylene 95-47-6 C8H10 106 6.53
Benzene, 1-ethyl-3-methyl- Toluene, m-ethyl- 620-14-4 C9H12 120 8.33
Benzene, 1-ethenyl-2-methyl- o-Vinyltoluene 611-15-4 C9H10 118 9.24
Benzenemethanol, 2,5-dimethyl- 2,5-Dimethylbenzyl alcohol 53957-33-8 C9H12O 136 9.36
Benzene, 1,2,4-trimethyl- Pseudocumene 95-63-6 C9H12 120 9.90
3,3,5,5-Tetramethylcyclopentene 38667-10-6 C9H16 124 10.89
Benzoic acid, methyl ester Methyl benzoate 93-58-3 C8H8O2 136 11.85
Naphthalene 91-20-3 C10H8 128 14.12
Naphthalene, 1-methyl- 90-12-0 C11H10 142 16.62
Naphthalene, 2-methyl- 91-57-6 C11H10 142 17.11
1,2,3-Trimethylindene 4773-83-5 C12H14 158 18.68
Naphthalene, 1,6,7-trimethyl- 2245-38-7 C13H14 170 22.93

Table 5: Nonspecific Compounds Tentatively Identified in THM-Py-GC/MS Analysis of Amber Objects
IUPAC Name CAS # Formula MW Retention Time, min
Methyltricyclo[2.2.1.0(2,6)]heptane 4601-85-8 C8H12 108 6.15
Cyclopentane, 2-ethylidene-1,1-dimethyl- 56324-66-4 C9H16 124 7.84
1,3,3-Trimethyl-2-(2-methyl-cyclopropyl)-cyclohexene 285129-06-8 C13H22 178 16.62
2-Buten-1-one, 1-(2,6,6-trimethyl-1-cyclohexen-1-yl)- 35044-68-9 C13H20O 192 19.73
1,5,9,9-Tetramethyl-2-methylene-spiro[3.5]non-5-ene N/A C14H22 190 19.82
Bicyclo[4.1.0]heptan-2-ol, 1beta-(3-methyl-1,3-butadienyl)-2alpha, 6beta-dimethyl-3beta-acetoxy- N/A C16H24O3 264 21.49
2-Methyl-4-(2,6,6-trimethylcyclohex-1-enyl)but-2-en-1-ol 62924-17-8 C14H24O 208 21.70
8-Acetyl-5,5-dimethyl-nona-2,3,8-trienoic acid, methyl ester 68799-74-6 C14H20O3 236 23.09
2-Methyl-4-(2,6,6-trimethylcyclohex-1-enyl)but-2-en-1-ol 62924-17-8 C14H24O 208 23.83
7a-Isopropenyl-4,5-dimethyloctahydroindene-4-carboxylic acid N/A C15H24O2 236 24.56
2-[5-(2,2-Dimethyl-6-methylene-cyclohexyl)-3-methyl-pent-2-enyl]-[1,4]benzoquinone N/A C21H28O2 312 25.17
Acetic acid, (1,2,3,4,5,6,7,8-octahydro-3,8,8-trimethylnaphth-2-yl)methyl ester 314773-27-8 C16H26O2 250 25.83
Acetic acid, 3-(6,6-dimethyl-2-methylenecyclohex-3-enylidene)-1-methylbutyl ester N/A C16H24O2 248 26.00

Table 6: THM-Py-GC/MS Results for Reference Samples
Peak Area Percentages
Sample Supplier GCI Identifier Succinate Diterpenes Fatty Acids
Amber varnish Zecchi VARN0084 0 0 77
Copal resin JPGM 0 36 0
Pine resin GCI NRES0244 0 74 0
Sandarac resin Verfmolen 'De Kat' NRES0295 0 19 0
Amber oil JPGM 1 1 3
Dominican amber JPGM 0 14 1
Amber (Dominican?) JPGM NRES0095 2 1 0
Amber Kremer NRES0005 3 2 1
Yellow amber Verfmolen 'De Kat' NRES0296 3 2 1
Amber Zecchi 10 2 2
Baltic amber JPGM 12 12 0.4
Amber Zecchi NRES0305 14 4 1
Amber Kremer NRES0004 20 6 1
Amber Kremer NRES0171 20 4 1

Table 7: THM-Py-GC/MS Results for Untreated Amber Object Core Samples
Peak Area Percentages
Accession # Succinate Diterpenes Fatty Acids
83.AO.202.12 13 1 0
82.AO.161.7 20 10 0
76.AO.84 24 5 0.4
83.AO.202.4 25 12 0.4
76.AO.79 27 11 0
76.AO.79 28 12 0.6
83.AO.202.18 34 7 0.7
83.AO.202.1 34 9 0.0
82.AC.161.285 35 4 0.7
76.AO.80 36 5 0.6
77.AO.81.24 38 22 0.5
78.AO.286.2 38 8 0.3
82.AO.161.4 39 9 1.1
78.AO.286.1 39 16 0
83.AO.202.6 41 8 0.9
82.AO.161.3 41 9 0.6
82.AO.161.1 46 7 0.3
77.AO.81.6 47 16 0.4
82.AO.161.2 53 4 0.3
82.AO.161.6 65 6 0.4
average 36 9.1 0.4
standard deviation 12 5.0 0.3

Table 8: THM-Py-GC/MS Results for Amber Object Core & Surface Samples
Sample Peak Area Percentages
Accession # Location Succinate Diterpenes Fatty Acids
82.AO.161.7 core 20 9.6 0.0
surface 4.2 9.1 0.8
83.AO.202.4 core 25 12 0.4
surface 16 4.6 1.6
83.AO.202.5 core 27 11 0.0
surface 11 1.7 1.5
83.AO.202.1 core 34 9.1 0.0
surface 11 2.0 1.5
78.AO.286.2 core 38 8.1 0.3
surface 29 4.3 0.7
83.AO.202.6 core 41 8.0 0.9
surface 12 2.0 1.2

Table 9: THM-Py-GC/MS Results for Treated Amber Objects
Peak Area Percentages
Accession # SampleLocation Treatment Succinate Diterpenes Fatty Acids
77.AO.81.29 core drying oil 34 5.2 18
77.AO.81.30 surface drying oil 13 4.6 7.7
77.AO.81.5 core drying oil 29 6.4 6.6
77.AO.81.4 core fatty substance 39 6.2 0.7
surface 23 2.7 8.1
77.AO.81.7 core amber oil - once 72 5.1 0.6
surface 44 7.6 0.4
77.AO.83 core amber oil - twice 38 5.6 1.9
77.AO.84 core amber oil – three times 54 2.9 0.4



Footnotes

  1. See Kalsbeek, N., and Botfeldt, K., “Identification of amber and amber imitations by infrared spectroscopy,” Meddelelser om konservering no. 1 (2007), pp. 3–11. Imitations have included materials such as Bakelite, nitrocellulose, polystyrene, and plant resins.

  2. See Rice 2006 for a discussion of amber and its terminology.

  3. E. Stout, C. Beck, and B. Kosmowska-Ceranowicz, for example, used infrared spectroscopy (IR) to compare and separate gedano-succinite from succinite; see “Gedanite and gedano-succinite,” in Anderson and Crelling 1995, pp. 130–48.

  4. See Waddington, J., and J. Fenn, “Preventive conservation of amber: some preliminary investigations,” Collection Forum 4, no. 2, (Fall 1988), pp. 25–31 and Shashoua, Y., National Museum of Denmark, 2002, http://www.natmus.dk/cons/reports/2002/amber/amber.pdf.

  5. Pastorelli, G., “Archaeological Baltic amber: Degradation mechanisms and conservation measures,” Ph.D. diss. (University of Bologna, 2009).

  6. Preusser, F., “Zur Restaurierung von stark korrodiertem Bernstein” (“The Restoration of Badly Weathered Amber”), Arbeitsblätter für Restauratoren 9, no. 2 (1976), pp. 75–77.

  7. See Bromelle, N., C. Beck, and G. Thomson, “Authentication and conservation of amber: conflict of interests,” in Science and technology in the service of conservation: preprints of the contributions to the Washington congress 3–9 September 1982, edited by N. Bromelle and G. Thomson (London, 1982), pp. 104–7.

  8. The relationship of Baltic amber and succinic acid was recognized in the early nineteenth century by chemists in Germany, where succinic acid was isolated using strong acids and bases. One study identified the amber constituent camphor (borneol) through smell.

  9. For an excellent overview of amber and resin studies see I. Angelini in G. Artioli, Scientific Methods and Cultural Heritage: An Introduction to the Application of Materials Science to Archaeometry and Conservation Science, (New York, 2010).

  10. Op. cit., Brommelle, N., et al., 1982, who first warned that most conservation materials will interfere with infrared spectra. D. Thickett discusses the problems of consolidant removal and the effects of solvents on amber in “The influence of solvents on the analysis of amber,” in Conservation science in the UK: preprints of the meeting held in Glasgow May 1993, edited by Norman J. Tennent (London, 1993), pp. 49–56.

  11. The earliest IR studies of amber were carried out most notably by J. Langenheim, C. Beck, and R. Rottländer. See, for example, Beck, C., and H. Hartnett, “Sicilian amber,” in Amber in archaeology: proceedings of the second international conference on amber in archaeology, Liblice, 1990 (Prague, 1993), pp. 36–47, and Beck, C., “Spectroscopic investigations of amber,” Applied Spectroscopy Reviews 22, no. 1 (1986), pp. 57–110. Amber studies have benefited from further developments in infrared spectroscopy such as Fourier-transform (FTIR), diffuse-reflectance infrared Fourier-transform (DRIFT), and Attenuated Total Reflection (ATR) FTIR. For the DRIFT method, see Angelini, I., and P. Bellintani, “Archaeological ambers from Northern Italy: An FTIR-DRIFT study of provenance by comparison with the geological amber database,” Archaeometry 47, no. 2 (2005), pp. 441–54. For the ATR method, see Guiliano, M., L. Asia, G. Onoratini, and G. Mille, “Applications of diamond crystal ATR FTIR spectroscopy to the characterization of ambers,” Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 67, no. 5 (2007), pp. 1407–11.

  12. For a summary of the use of the nuclear magnetic resonance method in amber analysis, see Artioli, Scientific Methods and Cultural Heritage, p. 383.

  13. See Shashoua, Y., et al., “Raman and ATR-FTIR spectroscopies applied to the conservation of archaeological Baltic amber,” Journal of Raman Spectroscopy 37, no. 10 (Sept. 2006).

  14. Mills, J., R. White, and L. Gough, “The chemical composition of Baltic amber,” Chemical Geology 47 (1984), pp. 15–39.

  15. See Shedrinsky, A., et al., “The use of pyrolysis gas chromatography (PyGC) in the identification of oils and resins found in art and archaeology,” Conservation of Cultural Property in India 21 (1988), pp. 35–41; and Boon, J., A. Tom, and J. Purveen, “Microgram scale pyrolysis mass spectrometric and pyrolysis gas chromatographic characterization of geological and archaeological amber and resin samples,” in Amber in archaeology: proceedings of the second international conference on amber in archaeology, Liblice, 1990 (Prague, 1993), pp. 9–27. For comprehensive overviews of the method, see “The application of analytical pyrolysis to the study of cultural materials,” chap. 6 in Applied Pyrolysis Handbook, 2nd ed., ed. Thomas Wampler (Boca Raton, FL, 2007), pp. 105–31.

  16. Gas chromatography effectively separates volatile, solvent-extractable components, which are subsequently detected and analyzed by the mass spectrometer. The limit to analyzing only the extractable components is mostly overcome by pyrolyzing the sample before the analysis. Pyrolysis uses thermal energy to break down polymeric and non-volatile materials into small volatile molecules that are amenable to gas chromatographic analysis.

  17. Stout, E., C. W. Beck, and K. B. Anderson, “Identification of rumanite (Romanian amber) as thermally altered succinite (Baltic amber),” Physics and Chemistry of Minerals 27, no. 9 (2000), pp. 665–78.

  18. Pastorelli, “Archaeological Baltic amber.”

ANCIENT CARVED AMBERS IN THE J. PAUL GETTY MUSEUM
Footnotes
Tables
Related Objects
Bibliography
To see the entire bibliography, click here.

MLA

. Ancient Carved Ambers in the J. Paul Getty Museum. Los Angeles: Getty P, 2012. museumcatalogues.getty.edu. Web. 15 Dec. 2018.

Chicago

. In Ancient Carved Ambers in the J. Paul Getty Museum, last modified August 1, 2012, accessed 15 Dec. 2018. Los Angeles: Getty Publications, 2012. museumcatalogues.getty.edu/amber/.

Permanent URL

<>