I have used salt vinegar or soda to set natural dyes when I have been dying my own fabrics. These are dyes made from natural things like Gum tree bark, or leaves, Walnut skins, onion skins etc flower heads etc. These dyes work best on natural fibers, like cotton silk wool, it does work, and heat is used to set the colour also. Many people are disappointed with the results only because they are used to seeing synthetic dyes which have intense colours. Organic naturals dyes are very soft and subtle and because of this one can be forgiven for thinking it hasn't taken.

Gal

"Do you have an issue with shrinking with a hot/cold wash? I usually just wash in cold and I have my dry on a cooler setting too. I hate shrinking. But I am also too impatient to prewash my fabric."[/quote]

I wash in hot water when I feel like it maybe a quilt that will need to be washed in hot water, for instance a baby or child's quilts that I am hoping will be used and abused until it can not longer be used. And then I will wash the cheaper fabric I might buy to use to learn something new or I need something quick and do not have the funds to buy the more expensive fabric. This way I am not disappointed in the shrinkage after it is made. If I am wanting the little shrinkage look I will wash in warm water and hot dryer after completing the quilts, but I only do that with the more expensive fabrics. But I always use a color catcher on the first washing of any quilt.

I hope I have answered your question and not rambled to much.

You are absolutely correct. Most darker fabrics bleed. To test it, but the fabric into a white tub or sink. If you see color, it is bleeding. Put in HOT water, vinegar and fabric. The trick is to let it cool down on it's own. I suspect that is what is happening when you leave it for your half hour to hour. After it cools, test it again to see if it is still bleeding. I had to do some dark greens for my granddaughter's quilt two or three times. It will save you heartache later. If it is STILL not setting, I was taught to use salt, although I have never had to resort to this.

Vinegar doesn't do anything to modern chemical dyes. But if you're putting it in the wash cycle with your detergent it'll kill your detergent.