FAQ: Do you buy certain cards to do these on?

I have purchased cut cards before, they come in a variety of types depending on your medium. Primarily I just cut up my own from high quality art paper that I already have.  The Acrylic, Oil and Watercolor papers will already be the right weight. Paper wise, I like to use 100lb bristol paper. The only requirement is that they be 3.5 x 2.5 inches.