Indiana and Vicenza limestone samples were treated with a mixture of an acrylic resin (B72) and a silicone resin (DF104). The samples were then aged artificially by subjecting then, to cycles of acid rain alternating with UV exposure. Because of the change in the appearance of the resin when examined by scanning electron microscopy it was decided that a more detailed study was necessary to understand the mechanisms involved in the aging process. To carry out this study, samples of both types of stone were treated with each resin independently, and also in a mixture. They were then aged by either UV or acid rain exposure. One set of samples was subjected to 400 hours in a climate chamber at 50°C, 70% RH, and was irradiated by UV light with an emission maximum at 280-380 nm and 125 W intensity the second set of samples was subjected to 80 hours of acid rain, using 0.02 M H₂SO₄ in a weathering chamber so that the acid solution would bathe the face of the samples at a rate of 0.01 ml per hour per cm₂. Specimens from each type of sample were examined by scanning electron imcroscopy to study how each factor influenced each type of resin independently and when in a mixture. The information obtained is discussed as a function of the actual aging that can be expected when this treatment is applied to outdoor sculpture and monuments.