
"What to do if you need to wash the silk. OK.....
First off, what you haven't yet stitched with, we are going to deal with differently than what has been used.
The unused silk, take that aside and begin rinsing in lukewarm water. Cold will not work as it is spun a bit tightly and will repel water. This works in your favor if you need to spot clean something in the future. Work the water into the skein, rubbing between your first two fingers and thumb to loosen any dye that may be hanging around. Scrunch if you like, you won't hurt it, but rinse and wring well. If there is still color in the rinse water, keep on going. The red you may want to let soak. Eventually, all the loose dye will come out and will be evident by the rinse water running clear.
I like to then lay the threads on a white paper towel to dry as any residual color will seep on the white towel, informing me I need to rinse more.
Silk isn't as problematic as the cotton, but I'm going to explain like it is the cotton, so if you find a lot of the steps unnecessary, then I apologize in advance.
For the silk that has been used, that will be trickier. Not to wash, but to prevent the colors from re-attaching onto your fabric where you do not wish them to reside. Tricky buggars those dye molecules. You shouldn't have too much trouble as you won't set the colors into the fabric but some may want to stick around. For this, I recommend using a special soap and I don't know if it is available in the UK. It is called syanthropol. It is a commercial soap for textiles that has an additive that wraps around dye molecules, preventing them from attaching where they aren't wanted during washing. Check your specialty quilting shops.
If you are unable to get any, let me know and I'll be happy to obtain some for you. It is relatively cheap and I believe shipping will cost more than the cost of the product (isn't that the way of things) BUT you can use it on any hand dyed item you need to wash."
I thought I'd have a look round the stitching show later this year to see if they have the soap there. Perhaps we can buy one bottle for the whole forum, and keep sending it round

Edited
Found some on eBay for £4 including postage, which isn't too bad!