'Kay I'm very stupid -- more reading has shown me that the acid dye in an all-purpose dye like Rit (which contains other dye in it as well such as direct dye) is likely what is causing such brilliant results with your silk. :) Sorry if you knew all of that already!

One brilliant website where I'm pulling this information from is here: http://www.pburch.net/dyeing.shtml Again, sorry if you've found that site already. :) It looks like you could even use things like vinegar, food colouring, and a microwave to tie-dye your silk! At least, that's what the website is telling me. So nifty!