Long-term accelerated aging in an environment free of ultraviolet (UV) light of dam mar resin films, containing the hindered amine light stabilizer (HALS) Tinuvin 292, shows that for best results the concentration of the additive may be increased to 3% from the previously recommended level of 2%, and also that the benzotriazole UV-absorber Tinuvin 328 can be omitted. Stabilized dammar films last virtually unchanged for 3,000 hours in the fadeometer and suffer only minor changes after twice that amount of time. Assuming that the law of reciprocity holds, stabilized dammar varnish would retain its transparency and solubility for more than 136 years in a gallery free of UV light illuminated at 1,000 lux. Because films of gum mastic are less stable than dammar films, they may need 4% HALS in order to be stabilized successfully. The results of tests on dammar and mastic films containing HALS, naturally aged for several years, confirm the results of accelerated aging experiments. Differential scanning calorimetry (DSC) reveals that the glass transition temperatures of dammar resin and gum mastic are lowered by the addition of Tinuvin 292. thereby lowering the brittleness of the resin films. DSC also shows that dammar and mastic are completely miscible with Tinuvin 292 up to an additive concentration of 3%.
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Rie et al. (1990) studied this question.
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