Dammar resin ageing

Dammar resin was introduced into Europe in the nineteenth century, mainly as a paint varnish It is still used today since it has good optical properties and low acidity. It is derived from various species (the genus Hopea and Shorea of the Dipterocarpaceae family). It is characterised by tetracyclic triterpenoids of the dammarane series and contains minor amounts of pentacyclic triterpenoids of the series of olanane, ursane and hopane. It also contains a polymeric fraction named polycadinene or [S-resene. Dammar resin triterpenoids undergo oxidation with ageing, as described for the components of mastic resin. 

Figure 3.11 DTMS total ion currents of (a) fresh dammar resin and dammar after (b) 1 week or (c) 2 weeks of artificial ageing. Reproduced from J. Photochem. Photobiol., A, 134, 13, Copyright 2000, with permission from Elsevier...

In addition to GC/MS, high performance liquid chromatography (HPLC/MS) has been used to analyse natural resins in ancient samples, particularly for paint varnishes containing mastic and dammar resins [34]. A partial limitation of chromatographic techniques is that they do not permit the analysis of the polymeric fraction or insoluble fraction that may be present in the native resins or formed in the course of ageing. Techniques based on the direct introduction of the sample in the mass spectrometer such as direct temperature resolved mass spectrometry (DTMS), direct exposure mass spectrometry (DE-MS) and direct inlet mass spectrometry (DI-MS), and on analytical pyrolysis (Py-GC/MS), have been employed as complementary techniques to obtain preliminary information on the... 

The first online TLC-MS attempt in the field of triterpenoids was done only in 2005 in the study of the photo-oxidation of natural di- and triterpenoid resins used as paint varnishes [10], The resinous samples were applied onto a cellulose-coated TLC plate, which afterward was subjected to direct MALDI-TOF-MS analysis without any development. The plates were only sprayed with a saturated ethanol solution of 2,5-dihydroxybenzoic acid as matrix to assist the ionization of compounds. Triterpenoids were observed as protonated molecules or as sodium clusters. Dammaradienone, dammaradienol, nor-a-amyrone, and dammarenolic, oleanonic, and ursonic acid were detected in dammar resin moronic acid, masticadienonic acid, and 3-0-acetyl-3-epi(iso)masticadienonic acid were found in mastic resin and diterpenoid abietane and pimarane acids were present in colophony. The induced aging process produced oxidized triterpenoids, which were observed in the MS spectra... 

In the nineteenth century dammar, a soft resin derived from trees of southern Asia was introduced in Europe and used for making colourless varnish. Mixed with oil of turpentine it has become the preferred varnish for oil painting, due to its superior optical properties and better ageing stability than the other natural resins. 

Comparison of the results of analysis of fresh and aged materials can lead to very different conclusions. For example, in the case of dammar and mastic, it is very easy to distinguish between the fresh samples of these resins, but after extensive artificial aging, dammar will retain its characteristic profile while mastic can give a completely unrecognizable one. °... 

It is a colorless to straw-yellow, oily liquid with a peppermint-like odor. It will darken and form a solid residue an exposure arxl aging. It is miscible with most organic liquids and it is a good solvent for such substances os nitrocellulose, ethylcellulose, law-viscosity cellulose acetate, polyvinyl chloride, vinyl resins, hydrocarbons, raw linseed oil, kauri gum, rosin, ester gum and synthetic rubber. It will only partly dissolve shellac and dewaxed dammar. 

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