Coasters are super easy to make. You can get these unglazed tumbled marble tiles at Home Depot. Be sure to wash them first and let them dry. Then use Staz On or another permant ink to stamp your images. You can color your image with almost anything. For this tile I used Fabrico Markers but I have used Sharpie Markers, Chalk and Classic Ink Pads before. When you are finished spray the tile lightly with Krylon (I use Matte Finish) and let it dry. Be sure not to spray to close to the tile or your ink and color will run. Always use the spray outside. Repeat once more and your coaster is done and ready to use.
Ink: Black StazOn
Accessories: Fabrico markers, Tile, Krylon Matte Finish