I found some treasure in the kiln on Friday morning. These lovely crystals had grown on one of the pots over the course of the firing. The firing went to 1270 Celsius (2318 F) and then the temperature was held for 2 hours at 1067 C (1952 F), and for a further 3 hours at 1135 C (2075 F). I tried this schedule after reading a paper by F. H. Norton, The Control of Crystalline Glazes, that had been presented to the American Ceramic Society in 1937. Under laboratory conditions in a special test kiln, Norton did extensive study of zinc silicate crystal growth, and discovered much that will be of value for my own experiments. He mentioned growing crystals with green centres and a blue border, and I followed a similar firing schedule to the one he was using. Here is a link to The Control of Crystalline Glazes, it is a PDF file.
The crystals are on a tall vase that I only just and so managed to fit into my kiln. After taking the vase out of the kiln, and grinding glaze runs from the foot, I raced down to the beach and took a few photos before packing the vase in a box. Then the tall vase, and 5 other pots were taken through to Oamaru for the exhibition that opens tonight at Pottery-On-Tyne. The vase looks terrific in sunshine and the blues really sparkle, but it takes on a grey look when the clouds come over. When the sun is out, the crystals make me think of peacock feathers!
|Crystalline glazed vase, approximately 20 inches high (508mm)|
Another pot that was in the same firing was this one, with a copper green glaze.
|Crystalline glazed bottle 15 1/4 inches tall (390mm)|
Interestingly, the crystals are quite a different shape from the ones on the tall vase.
|These crystals make me think of angels or dancers!|
Must go now. We have a stall at the Waikouaiti Food Festival at the race course today. I hope to go back and take some photos. Really cold start down there for us, our stall is in the shade of the grandstand and there was a frost overnight. Brrrrrrrrrrrrrr!