I've been wanting to use this landscape depth technique thing for quite some time now, I have a monthly project in progress right now that uses it but while I was doing that I thought it would be pretty cool to make this pair of frames with the positive and negative images in them.
The perspex is often labelled as Glass Green which gives a slightly false impression. The backing sheet is green and it gives the whole thing a lovely green tint. In reality this is the clearest perspex sheet I've ever seen and all the green tint goes away when the backing is removed. It's really good though if you want a Glass like material. I got it from Kitronik (again)