It might be too difficult to work with on a whole skein (or multiple skeins), but there is something called Discharge Paste at Dharma Trading. <a href="http://www.dharmatrading.com/html/eng/1574-AA.shtmlIt">http://www.dharmatrading.com/html/eng/1574-AA.shtmlIt</a> says it works on natural fibers, including silk, and it will remove acid dyes.