Report Oxblood Glaze, How To Have A Green Where The Glazed Is Not Reduced in Clay and Glaze Chemistry Posted November 2, 2015 If you're looking for copper reds, many an undergraduate student is advised to start with a celadon base glaze and add copper. Celadons were traditionally used on stoneware clay (think Koryo dynasty in Korea), not red clays. A tiny amount of iron from the clay body leaching into the glaze is the source of the green. If you start adding it to the glaze itself, it becomes too intense very rapidly. In my experience, the iron will overpower the copper. That's not to say you won't get an appealing colour of some kind, it just won't be the effect you're looking for here. Diesel; Let me get this straight. Do you begin with a Celadon glaze that already has 2% iron in it, or do you get the iron from the clay body and the copper is added to a plain clear glaze to get the copper red? TJR.