Crystalline Glaze Firing Unpacked

Close up of crystalline glazed pot with titanium, iron, and cobalt

This morning I unpacked another small load of crystalline glazed pots from my electric kiln, and filled the kiln up again with pots for a bisque firing which is taking place as I write. (By-the-way, I notice that Blogspot has put Friday at the top of this post... well, it may be where ever Blogspot lives, but it is Saturday here!)

Two crystalline glazed pots, the one on the left has titanium, cobalt and manganese in the glaze.

I had started off the glaze firing on Wednesday evening and got up at intervals through the night to check progress. By 5.15am the kiln was at 800 degrees Centigrade and reached 1260 degrees Centigrade at about 9am, and with cone 9 down I switched off. An hour later the kiln was at 1090 C and I switched on again and began the part of the firing where the crystals were allowed to grow. I held the 1090 temperature as closely as I could (I have a manual kiln). Three times in this growing period I switched the kiln off, and let the temperature fall to about 1030 C, then I held that for 5 minutes, then brought the temperature back to 1090 C again. Every time I did this, I caused a growth ring to form in the crystals. I switched the kiln off for the final time at 4.30pm.

Close up of the pot on the left showing well formed growth rings in the crystals.

Through most of the 6 and a half hour crystal growing period, I checked the kiln about 50 times (I can tell that from my kiln log), which meant a trip out to the kiln shed each time. Good exercise, and much needed! At the same time as doing the firing, I was sorting out paintings and pots to go to a local art and craft exhibition (Laura and I are guest artists), writing and printing an illustrated price list, packing the paintings and pots, and delivering the work to the exhibition at our local village hall.

There were some interesting pots in this firing, particularly where
I had put two different crystalline glazes over each other,
something I intend to do more of.

In addition to all that I opened our gallery, and tried to do some house work . Laura had been away in the North Island staying with her parents who celebrated their 50th wedding anniversary, so I wanted the place to be a little bit orderly for when she returned!.

A small addition of manganese seems to make 6 sided shapes appear in addition to the round crystals. It is an odd effect as the shapes reflect the light like lenses, but are almost invisible when looked at straight on.

I didn't succeed in making as much progress with the house as I would have liked, but my endeavors did uncover something horrid under the little rug in the kitchen...

I find it useful to put nearly dry work on top of the kiln whilst it is firing. If you look carefully you will see that I like to sit the pots on a wire rack or on kiln furniture to allow the air to circulate around the pot, and to prevent the pots from getting too hot.

... 4 dead and flattened lizards! Yerk! Nigella had been catching them (I have found her with others), but I had not realized that she had also been posting them under the rug!

One of my glaze testers showing very strong, dark growth rings
The glaze contains some titanium, manganese and iron. The
glaze testers are that funny shape in order to catch the run off glaze.

In the evening I drove out to Dunedin airport to meet Laura, and had her home just after 9 in the evening. It was quite a long day really.

This is a similar glaze on a vase, in this case the markings are quieter than on the glaze tester. The thermal mass of the pot, and its position in the kiln have quite an effect on the way that a glaze turns out. A small pot may react faster to changes in temperature in the kiln.

Laura had a good time with her parents, and quite a number of family and friends were able to get together for a celebration with them. Laura's parents were married on 5th of November (Guy Fawkes Day), so Laura was delighted to be able to purchase a few fireworks to let off in the evening.

This was the largest pot in the firing at about 10 inches high (255mm)

The largest pot that I fired has some really subtle effects in the "background" that surrounds the crystals. The colour graduates from the palest blue at the top, through yellows to green in the lower part.

Here is the entire kiln load... not many pots really, but for these glazes it is probably best to keep the pack in the kiln fairly open to allow it to heat up and cool down quickly.

Tomorrow I have to smooth the bottoms of the pots. I had time to separate them from their glaze catching saucers this afternoon, and to do a basic smoothing of the worst of the glaze runs with an electric bench grinder. Tomorrow I will finish up by hand.

I did promise you more photos of my journey down the length of New Zealand..... but it is now nearly 10.30 at night and I need some sleep.. So I will try again next time!