These are my cheap version of a bass relief (http://en.wikipedia.org/wiki/Relief) done on cheap (5 for £2) little canvasses, with a tub of £1 ready mixed plaster/putty from a hardware shop, and a normal kitchen knife used as a pallette knife.
I have ambitions to do giant alien cityscapes or parthenon-style battle epics with this in the future but at the moment I’m experimenting with how much detail I can add (given that when you imprint the wet plaster it often sags back) and how strongly the plaster will stick to the canvas (I will experiment with varnishing and maybe mixing the plaster with PVA to make it a bit more flexible). It might work better on rigid canvas board.. it’s a bit limiting because the plaster can only be about half a cm thick – but it’s a lot cheaper and easier than marble!
I’m also going to experiment with colouring them – how the plaster holds ink, watercolour and gouache, and acrylic paints… they’re quite nice unplaited though, I love how the shadows change emphasising different bits as you view them from differnet angles. I’ve had to fiddle a bit with the brightness and contrast in GIMP so that you can see the detail from the scan.