Growth rings, Ginger meets the Red Baron!

Firing crystal glazed pots is full of challenges. One thing that I have been trying to do for a little while is to make "growth rings" in the crystal formations. The firing that I did on Tuesday of this week was the first one where I managed to get some nice clear growth rings, and it feels good to have made some progress there.

This pot, shown in strong sunshine in my studio, is about 9 inches (23cm) high and the crystals are mostly about 1.5 - 2 inches (4 - 5cm) across. The background colour graduates from a pale tone near the top of the pot, to a much darker shade lower down. There is manganese and cobalt in this glaze.

I was beginning to have some doubts as to my chances of achieving the growth rings in my kiln as, not only is it entirely manually operated (no controller..., just me), but I wondered if it was not able to climb or fall in temperature fast enough. Several previous attempts had produced hardly anything that could be seen.


The way to get the growth rings is actually quite simple, but I had to do a series of tests of times and temperatures over several firings to sort out how to do them.

There are two fairly critical times in a crystal firing, one is establishing the right maximum temperature (a few degrees over or under can make a considerable difference), and the other time is in the cooling part of the firing, where the kiln is switched on again and the temperature held for several hours to grow the crystals. I do this at approximately 160 degrees Centigrade (320F) below the Cone 9 top temperature (Cone 9 happens at about 1255C (2291F) in my kiln).

In theory, if you make little spikes or troughs in the crystal growing temperature at intervals, you can cause the growth rings to form in the crystal. For those who might be interested????? I found that I needed to drop the temperature 30 -50 degrees Centigrade (85 -120 F), hold the low temperature for about 5 minutes, then climb back to the crystal growing temperature on full power. The short hold at the bottom of the trough seems to help make the rings much clearer.

This little test pot is about 5 inches (12cm) in diameter

I unpacked Tuesday's firing late Wednesday afternoon, and had the kiln loaded and firing by 8pm Wednesday evening. I fired all through the night and switched the kiln off at 10.30 this morning. Owing to the hands on nature of my kiln, I only managed 3 hours sleep in the night, but had an hour or so sleep before lunch which helped a lot.

These are really ice-like

I did the rough grinding of glaze off the bottoms of the pots this afternoon, and will finish them tomorrow.

This green pot is about 9 inches (23cm) high

Laura and I are taking part in a group exhibition at Gallery on Blueskin, Waitati, just North of Dunedin. The exhibition opens Saturday at 1pm. Laura will have some paintings at the exhibition, and I will have new crystal glazed pots. I'm hoping for some more pots for the exhibition from the kiln when I unload it tomorrow.

This white crystal on off white background is hard to photograph,
the background was picking up colour from other objects.

Ginger slept on my bed last night (glad that someone did!!), and, after having an early breakfast, disappeared on a dawn patrol. I think he may have run into a bit of flak over enemy lines, or even met the Red Baron, because..., when he arrived for his next breakfast he looked like he had been fed through a combine harvester! The poor fellow was splashed with mud and had lost tufts of his fur like a well loved teddy bear. He ate his breakfast with a quiet determination, then slept for most of the day and feels better now.