How do you set the dye in a silk shirt?

I have a collection of old, thin, pure silk shirts that I would like to cut up and use to make a quilt. How do I set the dye in them so it won't bleed over into the other pieces? I don't know what kind of dye the manufacturers used.
These are shirts that are already commercially dyed. The dye bleeds when you try to wash them. I need to know how to set the dye.

Many people have success with a vinegar bath to set silk dyes. When raw silk is dyed it is dyed in an acid based dye-bath. The acid help the silk react with the fibres so the colour sets. One of the easiest to find acids is acetic acid, also known as vinegar. Your silk might not be losing dye, it might be excess dye that's sitting on top of the fibres and is merely rinsing out. Try the vinegar trick, regardless, it will help the silk hold onto its color.

This is Paula Burch's excellent site on dyeing fibers and fabrics:
http://www.pburch.net/dyeing.shtml
And here's a site about dyeing silk: http://www.wormspit.com/dyeing.htm wormspit.com has everything you ever wanted to know about silk, and then some.

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