"Disappearing" tailor's chalk

[Barb T]

I worry a bit about what chemical is in the "disappearing" chalk (iron-out) and what its effect over the long term might be on tartan. If I were making a garment that would be worn for a few years and then given to Good Will, I wouldn't worry. But, a kilt may be handed down from person to person, and, given the fact that regular clay, dust-off (wax-free) chalk works perfectly well and isn't hard to find, I'm not willing to risk using the disappearing stuff.