There is a good list-serv for marblers hosted on yahoogroups, and periodically someone will organize a paper exchange. I just sent off 30 5 x 7 paper samples to a fellow in Denver, and in return I’ll get back a little packet with samples from 24 (or up to 30) different marblers. It’s a fun way to see what different people are doing. My samples were done on a metallic plum-colored paper. It was an interesting experiment and I liked the results, but it’s probably not a method I would use very often.