I'll have to try the tracing film and paper and maybe get a thinner modelling tool too.
The laser image transfer is simple:
1. Print a mirrored image to plain copy paper, only the outlines to be traced. The ink comes of from glossy papers easier and heavier papers don't stretch so much but usually if your paper starts stretching you're using too much acetone.
2. Tape the paper printed side facing dry leather.
3. Trace the lines using makeup remover pads or soft cotton soaked in acetone. Usually just a small amount of acetone is enough. I found it easiest to use nail polish remover because it's easy to get the right amount from the bottle. If you're doing it correctly you should see how the ink fades away from the paper and moves to the leather.
4.Remove the paper and case the leather.
5. Do your carving.
Notes:
-I've never had any problems with acetone damaging the leather. You're applying the acetone to the paper, not the leather and because it evaporates so fast, the small amount that ends up to the leather doesn't do much and you're going to oil the leather after carving anyway.
-Getting the lines the right width takes some testing. If the lines are too thin they don't transfer nicely but if they are too thick they might show after carving. If you're lines are the correct thickness they basically disappear in the carving process. If you dye the leather or use antique paste it will mask any remnants of the toner. However if you intent to leave the leather natural you might see some traces of the lines after carving.
If you try this let me know how it went!
My inkjets ink seems too colorfast :D It doesn't come of with acetone, alcohol, deglazer, water, heat, you name it. I've already tried almost every chemical in the household and we have a lot It smudges a bit with Tokonole and Fiebing's Atom wax but doesn't transfer. I have to check but it's probably archival grade ink, maybe using a low quality ink would be easier