Cork has natural beauty. Paint onto flat cork with acrylics, oils, or opaque watercolor, allowing it’s natural color and texture show. If your paint does not adhere to the surface, coat the cork with clear acrylic medium first.
Cork is especially rewarding for collage because it tears well, leaving a lovely deckled edge.
You can cut cork easily, as well. Cork sheets, rolls, and squares are available from crafts stores.
[From "151 Uncommon and Amazing Art Studio Secrets"]