Thursday, July 1, 2010

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.

9 comments:

ang said...

gorgeous crystals as always peter, mastery is in your hands it seems..you must get a controller for your kiln, i have seen them on ebay for a reasonable price..rest well ginger.

cookingwithgas said...

really spot on!
We have folks over here who do crystals- yours are FAB!
Love the kitties- we had a red tom when I was growing up- he made red baby kitties for 10 blocks in every direction.
He was one tough cat!

Linda Starr said...

I've been working with some wood this week and those growth rings are spot on, love the white on white a lot and the turquoise is an unusual color. Ginger is quite the cat, hope you kiln load is great.

jim said...

hurray for the growth rings! peter, i was impressed by your crystalline progress before but i had no idea you didn't have a computer controller on your kiln. wow! you're more ambitious than i thought. great work, i love those big crystals.

Angie said...

Wow ...those crystal effects are amazing....wish i understood it all better ...but it looks impressive.
I wonder what Ginger was up to ????

My friend has found out that there is a pottery class close by ....I am going to investigate as it must be the end of the year time soon and maybe I could give it a go in September .

acte gratuit said...

Beautiful crystals!!! I've never been able to get a crystal glaze to work.

What I'm wondering is what you use to grind your pots? I've had a few new glazes run lately and don't want to ruin them chipping off the bottoms!

Thanks,
Emily in Japan

Peter said...

Hi Emily in Japan!
Lovely to hear from you, welcome to my site. Regarding grinding glaze runs off pots... (I've spent about 4 hours doing just that today getting pots ready for an exhibition). I do a rough grind first with an electric bench grinder, the sort that people use for roughly sharpening gardening tools, or chisels that someone has used to lever a lid of a paint tin!

I make sure I'm wearing eye protection, gloves, and a dust mask. I haven't had a breakage thus far, but I imagine that bits of flying pot or glaze fragments could do serious damage.

I find I can get quite a nice finish just with the bench grinder. I am very careful about it and don't apply much pressure.

After the bench grinder I follow up with a small hand held electric tool that is similar to a Dremel tool that model makers often use (not sure what these would be called in Japan, but there are pictures of Dremel tools on the net if you do a Google search). Mine will take really small grinding attachments (I feel like a dentist at work!) They don't do the job all that fast, but they do it well and make the glaze quite smooth again.

Hi Ang,
I may yet get a controller for the kiln, it would be nice to get more sleep than I do (not sure how long it would take me to learn to trust the newfangled thing..., I've never used one before).

Hi Meredith,
It would be fun to meet up with some crystal glaze potters (I don't know anyone whose doing such things here).
Your red tom sounds just the sort of fellow that our "kitten", Nigella Stopit, would like to meet. She startled us all by going on heat two weeks ago, and we had an unbearable time of it. She really went crazy, and I rather think that she didn't manage to find a tom that was still in working order around here (thank goodness!!).

Hi Linda,
Some really interesting crystal pots out of the kiln today, iron and cobalt do wonderful things in the glaze that I am using. Photos soon. Good to read that you are working with wood, I'll be popping over to your site tomorrow to have a look at what you have been up to.

Hi Jim,
Not "ambitious", just mad! My trouble was that I got some crystals first time I tried, so it has been all downhill ever since.

Hello Angie,
I was so pleased to read that you might give a pottery class a go. I do hope that you do. I would recommend having a look at "The Potter's Companion" by Tony Birks, your library could probably get it for you. It is a really nice book, and has been revised and expanded in recent years. All sorts of ideas about things to make, and good advice, and good photos too.

Arkansas Patti said...

I adored the green pot. You are such a talent.
You know I am going to comment on Ginger. Boys will be boys and boy cats are that squared.
May he continue to win his squabbles without involving a vet. Hope they involve a lady and not territory dispute.

Peter said...

Hi Patti,
Just thinking of you this morning and was wondering how you were, so it is really lovely to hear from you.

Old Ginger has no interest at all in the ladies... this matter was proved conclusively when Nigella Stopit went on heat a couple of weeks back. He was grumpy and hated the extra attention and provocative behavior of a hormone crazed Miss Stopit. He couldn't wait for life to be back to normal again. I suspect that the squabbles are very much territorial. Laura did witness seeing Ginger chasing a cat down the road one evening recently and into someone's place about two houses away from us. The fact that they have a large dog didn't seem to dampen his fury!