Oxidation dammar

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 5.6 GALDI mass spectra of dammar, fresh (a) and naturally aged under different conditions in a window after 7 weeks (b), as well as in the dark (c), under museum conditions (d) and in a window after 31 weeks (e) [36]. Strong oxidation and degradation can be seen after a few weeks under all ageing conditions, and the ageing patterns are very similar. Oxidation under museum conditions is not much more pronounced than in darkness...

Figure 5.7 GALDI mass spectra of mastic. Commercially available mastic (a) in an advanced state of oxidation as can be seen by comparison with really fresh mastic a few days after harvesting (b). As with dammar, oxidation and degradation progress quickly in both light and darkness. The same mastic as in (b) is depicted after natural ageing in the dark after 7 weeks (c), and in a window after 7 weeks (d) and 42 weeks (e)...

Examples. Data from an early experiment in which the gain in weight of dammar resin was observed, illustrated in Figure 8, indicate that a limit had been reached after one month (20). One may assume that the tertiary alcohol groups or the double bond in the vinyl groups, known to be present in this natural resin, were readily oxidized and that thereafter, one would need to increase the temperature or the energy of... 

Figure 8. Oxidative gain in weight of film of dammar varnish prepared from xylene solution. , under daylight fluorescent lamps at 240 ft-c intensity and 90°F, 20% r.h. , partially protected from the light in aust-free box.

A novel dimethyl ester -lactone from Dammar resin has been shown to have the structure (210) by AT-ray analysis. A very probable biogenesis from asiatic acid [(211)— (212) (210)] has been suggested. Madasiatic acid (213), a close relative of asiatic and madecassic acids, has been isolated from Centella asiatica Protection of the vicinal diol system, followed by oxidation to the 6-ketone and Wolff-Kishner reduction yielded 2o,3)5-dihydroxyurs-12-en-28-oic acid. Rubitic... 

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... 

When a solution of daimnar dries in high relative humidities, a bloom made up of small crystals of ammonium sulphate can occur on the surface. Dammar films can develop wrinkles during drying. The wrinkling appears to be the result of an initial oxidation of the resin combined with movement of the underlying solution. Mastic, which develops fewer wrinkles than dammar (Thomson, 1957), retains less solvent than dammar (Feller, 1957b, 1958). 

Typical constituents found in dammar and mastic resins. Scalarone, 2005 These are major components alongside many minor ones. Compounds a, b, and c are major components of dammar, b, c, and d are found in both resins, while e and f are found in mastic but not in dammar so can be used as markers for its presence, g and h are polymers found in small quantities in dammar and mastic respectively, i is a typical oxidation product of dammar and mastic. 

FIGURE A3.32 Solubility of dark aged dammar. — indicates the approximate limit of solubility when exposed to light and oxidation equivalent to 100 years on a gallery wall (Feller and Curran, 1975 of A3.33). Data kindly provided by Dr Greg Smith and Classes of2009, 2010 and 2011 of the Art Conservation Department at Buffalo State College. 

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