|Crystalline vase 170mm high (6 3/4 inches)|
|This 220mm (8 3/4 inches) pale green vase did not photograph well in the bright sun.|
|The vase has very pale green on green crystals.|
|There is a spectacular waterfall of colour on the rim where the outer crystalline glaze meets the inner glaze,|
|A page from my kiln log.|
Glazing, firing, waiting for the kiln to cool. Glazing, firing, waiting for the kiln to cool. Gl....... The cycle of work continues through every day regardless of Easter as exhibition deadlines loom closer. In the days that followed my previous post I realized that there was not sufficient time to have fountains made, tested, and any technical issues sorted in time for exhibiting in Oamaru in April, so a change of direction was called for. I opted to do crystalline glazed pots, and managed to get the pots made and dried in record time, by putting them on wire racks over the kilns as they were bisque firing some of my sculptural work.
I decided to make up four different glaze bases, two of which I have used before, and two more that interested me. I would use the first glaze firing to test all four of these, and use them on the smaller of the pots. Out of that firing, I had two pots that worked well, two more that did not grow crystals, but were a good colour, and another pot that was very under fired, and a couple of interesting tests. One of the pots that worked (the one in the first photo of this post), had one of the untested glazes on. Ha, Ha... maybe I shouldn't bother testing glazes ever again!!! I was very pleased with the definition and detail of the crystals.
I had a good look at the pots, tried to think about what had worked and what had not, then glazed enough pots for a second glaze firing. I finished firing the second kiln load yesterday.
To give you a bit more idea of what goes on in a firing of a crystalline glazed pot, I have included a photo of my kiln log from the second crystalline glaze firing. I have a manual kiln, with no controller, so I have to twiddle simmerstat knobs, note temperatures, and keep track of the progress of a firing, by writing it all down on graph paper. The numbers along the bottom of the graph are the hours. I started the firing just after 8 in the evening. Below the time line are comments such as "All 1.5" These refer to the simmerstat settings on the kiln. If you look along a little way, you will see me turning the kiln on Full just before 3 in the morning, and the kiln getting to peak temperature at just after 7 in the morning. The numbers up the left side of the graph, from 0 - 13 are temperatures. I work in Centigrade, so the top one is 1300 C. This firing reached about 1275 C which is 2327 Fahrenheit.
You will notice how the kiln is fired to the peak temperature, then the temperature drops to about 1100 C, and is held for several hours. This time where the temperature stays around 1100 C very important, as it is where the crystals do their growing. You will see a short dip in temperature after about 2 and a half hours, this was done to form a growth ring in the crystals. You will also see a two hour period at the end of the crystal growing time, where the kiln is held at a lower temperature, this encourages the crystals to have a defined margin around the outside. Sometimes this can become a dark outline.
There is rarely enough room at the bottom of the graph to write all the information that I need when I am doing the crystal growing part of the firing. I have to check the kiln every 10 to 20 minutes throughout that period, so I write any information that I need to record in a block above the timeline. You may be able to read some of that... , or maybe not, my writing is a terrible scrawl! Most of my notes are of temperatures, times, and simmerstat settings.
I am currently waiting for the second glaze firing to finish cooling. I should be able to unload it first thing tomorrow morning.
|Easter is late summer for us. This is how things looked this morning at the beach!|
The exhibition in Oamaru that I mentioned is one that the potter's group in Oamaru is holding at their clubrooms. The Oamaru potters are a friendly group of people, and I am looking forward to catching up with them. The exhibition opens on Saturday April 6th at 7pm, and runs until April 12th. You will find it at Pottery-On-Tyne, 44 Tyne Street, Oamaru. Bevin Stowell, from Ashburton, and I are both guest exhibitors.