the surface that is under my drawing is a big piece of thick carboard that I have painted a few years ago with the purpose to place it on my desk to work and also to take the photos... ;-) I had made a tutorial post at this time, I will try to find it or to eventually make another one  ^_^  
Now the colors are not as vivid as it used to be and of course it's a bit damaged by use, but this makes the job  ;-)