Wolve,
Someone did mentioned LDPE: Low Density Polyethelene the last time but I don't have that.
I tried on an x-ray film this afternoon, it didn't rise high enough to give you a good impression on the leather. Then I used a piece of plastic that someone from NC gave me, it did pop up a little better and produce quite a visible impression.
As this is my first time trying it out ( not a pattern ), this is what I can say; if you'll to trace directly onto the plastic, you need a very fine marker pen as the engraver (mine) is pin pointed. After tracing, you turn the plastic the other way so that you're engraving a 'mirror' image. Later I found that it maybe better if I'll to trace it on a tracing paper then turn the paper around and place the plastic over it for engraving. It's almost midnight over here, too noisy to try it. If I find the time tomorrow, I'll tell you more.
At the meantime, maybe our friend whom he received a piece from Verlane can tell us how he did it -
Brandon