Silk can be trickier to dye than cotton because it is a protein-based fiber like wool or camel hair. To add long-lasting color, you need open the cuticle of the fiber so the dye can reach the shaft. The cool down is equally as important so the cuticle will close again. You must change temperatures gradually, without overheating, or you will damage the fibers.
Wet the fabric so it is well saturated to help the color attach more easily to the fibers.
Mix the dye solution in a dye pot over a heating surface such as a stove and add the fabric. Slowly bring the temperature to 120 degrees. Stir the fabric frequently for a more even coat.
Add vinegar to the pot and keep the solution at that temperature for at least five minutes, depending on the instructions on the dye box. Continue to stir the fabric.
Turn up the temperature to a full simmer, letting it simmer for at least five minutes, stirring frequently. Turn off the heat, and let it cool completely.
Remove the fabric and lay it flat to dry.
Dye stains, so work with tools and surfaces that will be OK if they get color on them.