I've used this idea on candles and wondered if it would work on soap, but first you need to find a square (or rectangular) cake of soap. Some soaps are contoured. They won't really work for this application.here and resized it in Photoshop. I printed it out and placed it on the bed of my copier (not computer printer). Next I taped a piece of ordinary white tissue to a piece of copy paper and hand fed it into the copier.