Originally Posted by
Sewnoma
You know, I was thinking...if heat from the dryer sets runs and stains, wouldn't it help set dye in newly purchased fabric too? Without washing first, just throw it into the dryer and let it get hot?
Heat sets some organic dyes (and definitely organic stains! Try dropping some carrot juice on your socks, the way I did, to confirm.) Almost all dyes used on fabrics these days are chemically-based. Heat alone is usually not enough to set them; that's why factories use chemicals to permanently set the dyes.
In short, tossing in a dryer will not set most dyes (but will set some stains).