Hey, those of you casting buttons, have you checked out Cyro? They have some compounds that are supposed to be really good for light diffusion ("Acrylite DF"). Dunno if they can be used with cold casting or not. I'd give direct links to the products, but their site uses session cookies heavily and I didn't feel like reverse-engineering the URL to make a simple link. Just click on FAQ and enter "Diffusion" in their search engine...