Crystal glazes, aka crystalline glazes, are glazes that have crystals grown in them during firing, crystals that can look like flowers, shells, or many other things, wherever your imagination takes you. To make them, a special glaze mix, high in zinc and alkali metal oxides, is applied to a pot which is then fired in the kiln to over 1200C, then the temperature is allowed to fall to 1050C, when crystals of zinc silicate will start to grow in the – still liquid and red hot! – glaze. The temperature can just be held there for 2-3hr, or raised again then lowered again to get a layered effect. Results are unpredictable, as the crystals sometime just don’t appear, sometimes cover the whole pot; and the glaze is so runny, it runs off the pot, which has to be raised over a receiver to catch the drips and stop the pot fusing to the kiln shelf and then cracking as it cools – the unpredictability makes for lots of rejects, but the successful pots can look marvellous. See my photo gallery for examples!
Chris Heneghan Potter 