Mastic 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. 

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... 

The resin composition was indeed found to influence the ageing processes in mastic, the polymer fraction was shown to reduce the oxidation of triterpenoids (Figure 5.8). This was found for both natural ageing [33, 36] and artificial ageing. Because the polymer, a polymyrcene, contains many double bonds that can easily be oxidised [42], it might act as a radical stabiliser. The mastic samples shown in Figure 5.8 were obtained from three aliquots of the same mastic solution, the polymer part of the first aliquot was removed and added to the third. 

P. Dietemann, M. Kalin, R. White, C. Sudano, R. Knochenmuss, and R. Zenobi, Chios Gum Mastic Freshly Harvested vs. Commercial Resin and its Implications to Aging of Varnishes, Z. Kunsttechnol. Konserv., 19, 119 130 (2005). 

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... 

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. °... 

Rosin family s most common form of adhesive is colophony, a hard amorphous substance derived from the oleoresin of the pine tree. This material is applied in solvent solution form as a hot-melt mastic. It has poor resistance to water, is subject to oxidation, and has poor aging properties. Plasticizers are usually added to reduce its brittleness. Bond strengths are moderate and develop rapidly. These materials are used as temporary adhesives in bonding paper and as label varnishes. They are also used as components of PSAs based on styrene-butadiene copolymers and in hot-melt adhesives and tackifiers. These materials have been largely replaced by synthetic-resin adhesives. One specialized form of rosin adhesive is Canada Balsam, covered by the obsolete Military Specification MIL-C-3469C, titled Canada Balsam. This material was intended for cementing optical elements. 

Resins largely amorphous, solid or half-solid, transparent, odorless and tasteless organic substances, usuaUy of vegetable origin. Tree R. are clashed according to age into fossil R., such as amber, recent fossil R. (several years to centuries old), e.g. copal R and recent R., which occur mostly as balsams fresh from injured trees. Caoutchouc (see) is included with the R. Herbaceous plants produce R., e.g. mastic, but not in any considerable quantity. Mixtures of R. with mucin are called gum R. Solutions of R. are referred to as balsams. The most important animal R. is shellac, produced by the female East Asian scale insect (Tachardia lacca). 

The botanical species exploited in the past for the collection of resins vary according to the geographical area, and thus, the availability of adequate reference materials of a known botanical origin is crucial for resin identification. Pine resin and resin-derived pitch, mastic, frankincense, myrrh, benzoe, and birch bark tar are the most common terpenoid materials in archaeological artifacts from the Mediterranean area. Terpenic resin composition depends on aging and exposure to air and light, so the biomarkers used for their identification are... 

Mastic and sandarac, which are soluble in alcohol, were formerly used as varnishes, particularly in the Middle Ages, for the protection of oil and watercolor paintings or for coating metals. Sandarac is the resinous exudate of Tetraclinis ar-ticulata (Cupressaceae) and mastic is obtained from Pistacia lentiscus var. chia (Pistaciaceae). Mastic is still collected on the island of Chios in the Aegean it was once the monopoly of Greek emperors. Its use to sweeten the breath and for dental purposes was first recorded in 400 B.C. (19). 

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