If you're looking for fabric dye "fun", check out the Dharma website. I've not seen anything about viscose-rayon but there's info about viscose-cotton or rayon alone among the material on these pages http://www.dharmatrading.com/topnav/dyes/ You may get somewhat different colours depending on the fiber content: no "complete dying formula" but fun, for sure, if that's what you're really after....