Apparently you should use the light coloured kinds and, just my opinion (not tried it) i'd avoid the fancy rosins with gold dust and stuff in them It's not hard to see the image once you have it in the right place held up to the light (so it looks like a positive). It's really quite impressive. Bruce in Australia on here first posted photos of one a few months ago which got me interested in it. He posted in the above thread as well if you want to see his photos. His are much more impressive than mine!