grade I highly recommend this way of coloring them. That way the glaze won't fill the holes. They break if you stack them horizontal! Also, do not use air dry clay, as they are too fragile. Stoneware is a must.
Tut : Paper Marbling Made Easy - Most of us love marbled papers and most of us would love to do them ourselves but then get intimidated by such mysterious ingredients like the often used Carragheen for example and by the obvious