Copal identification

Pyrolysis in the presence of tetramethylammonium hydroxide (THM)-GC/MS allowed the identification of high- and low-molecular weight components in manila Copal and sandarac fresh and artificially aged samples. The pyrograms showed signals due to the polymer fraction and to free diterpenoids [43]. THM-GC/MS has also been used to determine the molecular composition of Pinaceae resins, allowing the study of fresh, naturally and artificially aged samples [16, 44 46]. 

The terpenoid resins commonly used as artists materials were colophony, Venice turpentine, mastic, dammar, copals and sandarac, and most of the scientific literature concerning the identification of Old Master varnishes and the study of their degradation focuses on these resins. 

Analytical pyrolysis has been proven a very useful tool in the identification of resins used for artistic objects [16,17], The pyrograms of Manila copal, colophony, Venice turpentine, elemi, shellac, dammar, sandarac, and mastic were obtained and used as fingerprints for these materials. Manila copal, colophony, and Venice turpentine were characterized by the presence of a degradation compound from abietic acid (as the source of these resins is from species of Coniferae), probably methyl-isopropylnaphthalene. Elemi has a characteristic peak for elemicine, shellac showed a series of fatty acids, dammar showed the presence of sesquiterpenes (see Section 6.3), sandarac was characterized by a phenolic compound, totarol, and mastic was also identified by specific sesquiterpenes [17]. 

Amber, colophonium, copals, mastix, and shellac develop a beautifully blue color when in contact with ether mixed with ammonium molybdate (0.1 g in 5 ml concentrated sulfuric acid) and ammonia. Thinius reports a number of additional color reactions for the above natural resins, but these do not permit unambiguous identification in each case, especially since phenolic resins produce similar colors. 

A. M. Shedrinsky, T.P. Wampler, and N.S. Baer, The Identification of Dammar, Mastic, Sandarac and Copals by Pyrolysis Gas Chromatography, Wiener Beiichie uber Natur-wissenschaft in der Kunsi, VWGO, Wien (1988). 

Shedrinsky, A.M., T.R Wampler, and N.S. Baer, The identification of dammar, mastic, dandarac and copals by pyrolysis gas chromatography, Wiener Berichte fiber Natur-wissenschaft in der Kunst, Doppelband, 4/5 (1987/88), pp. 12-25. 

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