Changes during the aging of dammar resin films containing the antioxidant Irganox 565 were observed using ultraviolet-visible light transmission spectrophotometry and solubility tests. The concentration of the stabilizer was monitored with the aid of high performance liquid chromatography. Although the additive stabilizes dammar during heat aging in the dark, it breaks down rapidly during fadeometer aging and during natural aging behind a window facing south. Furthermore, colored degradation products of Irganox 565 cause increased yellowing during combined fadeometer-heat aging. In view of the fact that light plays an important role in the autoxidation of dammar, Irganox 565 is not recommended as a stabilizer for dammar varnishes.