Retayne is a dye fixative. Everyone needs this! I learned from the guest speaker at the last Huron-Perth Guild meeting that vinegar and salt do not fix the modern chemical dyes. When natural dyes were used they did the trick. But now, even though fabric bleeding occurs a lot less often, there are times the dye will run.
I love to hand dye fabric but was not so fond of the rinsing. After 20 minutes of rinsing, you let the fabric sit for 5 minutes. When you start rinsing again, it looks like you hadn't done any yet. But, after soaking the fabric in Retayne for 10 minutes, not a speck of dye comes out. It saves hours of work and tons of water.
You can use Retayne to stop colour running in your regular wash too.
You may have heard of Synthrapol. This product is more like a soap. Dyers use it to remove any sizing or other fabric treatments from fabric before dyeing. It helps the fibres be open to chemically bond with the dye. After dyeing, use it to scour the fabric clean of residue.