ANALYTICAL APPROACH
Identification of a Late Bronze Age Resin
Hampton H. Hairfield, Jr., and Elizabeth M. Hairfield John Baker Daffin Laboratory of Chemistry Mary Baldwin College Staunton, VA 24401
A late Bronze Age vessel, shipwrecked at Ulu Burun near southern Turkey, has been called the archaeological find of the century. Found in 1982, it is the oldest ship discovered (dating back to the fourteenth century B.C.) and its diverse cargo spans seven civilizations (1, 2). Among the numerous items found were approximately 100 amphorae, or jars filled with a yellow resin. This resin was one of the most abundant commodities in the cargo. The precise identification of t h e Bronze Age resin is important for two 0003-2700/90/0362-041A/$02.50/0 © 1989 American Chemical Society
reasons. It is the first archaeological discovery in which resin has been found in abundance, and identifying the resin can provide information about the ship's point of departure and its destination. Resins, the solid or sticky semisolid secretions from various plants and trees, have been used since ancient times to prepare incense, medicine, cosmetics, and perfumes. Today they are also used to prepare varnish and cement. Of the many resins that have been important since antiquity, terebinth, mastic, and frankincense (olibanum) are likely candidates for the Bronze Age resin because of their yellow color. The source of the terebinth resin is Pistacia terebinthus, a tree that grew abundantly in ancient times in the
Mediterranean region. This resin was called "sntr" by the Egyptians, who burned it as incense to worship their gods as far back as the 18th dynasty (1500 B.C.) (3). In fact, because the Egyptians burned such large quantities of this resin, it seems likely that a large cargo of terebinth would be destined for Egypt. Mastic, a resin secreted from Pistacia lentiscus, is a close relative of terebinth and native to the Mediterranean region. During the lifetime of Christ, mastic was more valuable than frankincense (4). It was used to prepare medicine and embalming mixtures in ancient Egypt (5). Because terebinth and mastic resins are similar in geographical origin (6) and odor, it would be possible to confuse one resin for the other. Frankincense, one of the gifts of the Magi, came from Arabia and the Horn of Africa. It is secreted by trees of the genus Boswellia and could have made its way to Egypt via trade routes that date back to the fifth dynasty (2800 B.C.). However, there is no official record of the resin in Egypt until the 18th dynasty (4).
Identification of resins For complex mixtures such as resins, IR spectroscopy has limited usefulness; the spectra only provide information about which functional groups are present in t h e substances. Because these resins contain both acids and esters, their spectra are virtually identical in the 4000-1250-cm -1 region. However, resins often afford a characteris-
ANALYTICAL CHEMISTRY, VOL. 62, NO. 1, JANUARY 1, 1990 · 41 A
ANALYTICAL· APPROACH tic band in the 1200-700-cm.-1 region. For example, amber can be identified by succinate absorption (a sharp peak preceded by a broad shoulder in the 1200-1150-cm- 1 region) (7). Unfortu nately, no characteristic IR bands were found in the Bronze Age resin. Gas chromatography/mass spec trometry (GC/MS) has been used suc cessfully to identify triterpenoids in resins. Sample preparation involves ei ther steam distillation of the essential oil fraction (which is volatile and can be analyzed by GC or GC/MS) or extrac tion of the acidic fraction followed by esterification with diazomethane. John Mills and Raymond White of the National Gallery in London stud ied the Bronze Age resin using GC/MS. In the methanohether (1:9) extract of the resin, they identified four acids as their methyl esters: oleanoic acid, mo ronic acid, masticadienonic acid, and i'so-masticadienonic acid (Figure 1). Because these acids are characteristic of resins from the genus Pistacia, Mills and White concluded that the Bronze Age resin is from this genus (8). Although they did not carry out fur ther analyses, they used an historical argument to speculate that the un-
COaR C0 2 R
Figure 1.
Methyl moronate
Methyl /somasticadienonate
Methyl oleanate
Methyl masticadienonate
Major acid constituents of the genus Pistacia resins (R = CH3).
known resin is terebinth. This theory was based solely on their belief that mastic resin was in short supply during the Bronze Age. A large terebinth tree could easily yield up to 2 kg of resin, whereas the more viscous mastic resin
25
Methyl oleanate
could only be collected one drop at a time. Thus Mills and White believed it was unlikely that the 100 jars discov ered on the shipwrecked vessel could be filled with mastic resin. We felt that it was essential to pro-
189
Methyl moronate
20 ο CZ CO "O
15 10-
c
393 7 300
9
400
γ
203
249
=3 -O
