I glue sized a bunch of heavy card stock and cut it up into small pieces. I wanted to do some relatively quick studies and didn't want to be inhibited by using hard to prepare or expensive grounds. The sized paper is very cheap and easy to make and I like the surface texture. I used it a lot when I was in art school. I mix a little red acrylic with the size because I like the warmth it adds. The point of these studies is to avoid being overly fussy. I want to keep them loose and to the point. Jason is a student of mine.