Beyond rust dyeing

This is more straightforward than rust dyeing, but may be more limited in the kinds of patterning and subtleties it produces. Importantly, though, it won't break the machine needle when it's being sewn.

The active ingredients are lemon juice and heat. I saw it here and tried it with some squeezed lemons (top and bottom) and by flicking juice at the fabric (centre). Let it dry, then iron, at which point the colour will appear.