Roo, I think Createx paints only require heat setting when using them on fabrics. Here's what I read on the labels of both the "transparent" and the "pearlized" Createx paints:
Shake well before using. When sparying , use of a mask is recommended. For permanence on fabrics: Heatset with a hot iron for 2 minutes, or shirt press 15 seconds. All other surfaces permanent when dry. May be diluted with water.
Maybe I'm not interpreting this right... and I'm not sure what the difference would be between fabric and leather, but I do know that if I put it on too thick or heavy, it can crack and peel or rub off after it dries. If I thin it enough to absorb easily into the leather, it seems to stay on quite well, and I've never done the heat set thing. I suppose I could reconsider if someone sent back an item I made that was in use a couple of years, and I found that the paint was coming off over time.
Kate