nice stuff, and fun to do. I (almost) forgot about this, but we used to produce a bunch of those in my art classes, ages ago. Easy to do and no fancy equipment needed. Of course they are one of a kind. Another way is to make variations: use a sketch under glass and then pull several new monotypes, starting anew each time, wiping the glass clean. If you work fast enough, acrylics work good for that, since they easily clean off glass.