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The deterioration of fossil resins (crazing, cracking, and darkening) was investigated by comparing the effects of one year of accelerated aging—specifically intensive exposure to light, heat, and fluctuating humidity, both individually and in combination—on samples from several natural resin deposits. These included two Cretaceous ambers (from Myanmar [Burma] and central New Jersey), two Tertiary ambers (from the Baltic and the Dominican Republic), and Holocene copal from Zanzibar. The five resins were chosen for their disparate ages and botanical origins (and thus chemical and physical properties), as well as their paleontological significance. In all cases, pronounced deterioration occurred under combined exposure to light and fluctuating humidity, based on surface crazing and a decrease in absorbance of light in the UV region (360–400 nm). While crazing did not visibly occur in cases of fluctuating humidity in dark conditions, or UV exposure alone, spectrophotometric evidence indicates that some deterioration did take place. Yellowing after exposure to elevated temperatures occurred in all samples tested, with the exception of Burmese amber. All four true ambers exhibited a decrease in UV absorbance after exposure to heat (while copal actually showed an increase). The samples from the five deposits represent three chemical subclasses of fossil resins, and each of the resins reacted differently to the various aging conditions, with New Jersey amber particularly unstable. Based on these results, amber collections should be stored in an environment with stable humidity, relatively low heat, and minimal exposure to light. Anoxic sealing and storage, and particularly embedding amber samples in a high-grade epoxy, may be beneficial, and further investigation is indicated.
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