so it was faked, like the thing they use to do caustics in poser? it's a good fake, anyway. the attached is what my attempt looked like in carrara. it's not as good as antoine's IMVHO, but it's easy to set up and only takes about 5 minutes to render. I tried doing a diamond caustic render in maxwell render, and it looked promising, even tho the default render settings caused it to be grainy, like a photo taken with bad film in a bad camera. but then I checked the maxwell render forum, and the dispersion setting apparently causes the render engine to crash, or at least to take many hours or days to get a good render. so maxwell render is no-go, at least for me. I also checked the maxwell render forum on why default renders are grainy - no answers, just more questions. keyword "grainy" didn't appear in the maxwell render manual, nor did keyword "diamond", and the "gem" shaders in the maxwell materials were actually shiny metals, not gems.