Hmmm... guess where I worked must use natural dyes because the vinegar really does work every time. There were a couple of times I forgot & boy did the fabric fade like crazy. And I haven't use RIT in many, many years. Just looked it up & sure enough they now say that vinegar won't work. I worry about chemicals, too, so it's unsettling that something with formaldehyde (even a little bit) is the only thing that would set the colors. Makes you wonder what's in the dyes themselves.