I realise that any form of communication, be it conversation, a written report, or biography, gives a filtered view of reality. A limited picture. Most people have a public face, a private one, and an internal world that no one gets to see.
With crystalline glazing there are successes and failures in roughly equal proportions. I realize when I look back through my blog that I have said very little about the pots that did not work out, yet these pots are a very real fact of life. This makes my blog rather unbalanced... too much glitter and success, and not enough disappointment and honest toil! So, to bring things back to a place that is nearer the truth, I have posted a few pots this time that haven't worked.
Recent Pots With Problems!
Here is an example of a glaze with too many crystals. This pot needed to be fired to a higher maximum temperature, and probably held at that temperature for a few minutes. The maximum temperature that you fire a crystalline glaze to determines the number of crystals. Too high, and you might get none at all; too low, and there are too many crystals. The margin for error is probably + or - 5 degrees Celsius.
You can correct this problem by firing a pot with the same glaze to a higher temperature, or by adjusting the glaze formulation. A little less zinc oxide might help here, and/or some more flux. An addition of one or two percent lithium carbonate could make this glaze mature several degrees lower. Glaze thickness can also affect crystal growth, and their quantity. In general, thicker glazes have less crystals, but they grow bigger. Thin glazes can have numerous small crystals, and can sometimes be unpleasantly "dry" in feel and appearance.
This pot has very uninteresting crystals and surrounding glaze. I also do not much care for the colour! The newly fired pot is shown still attached to its sitter and catching saucer. The sitter is a ring of clay of the same sort that the pot is made of, and it is matched to make a near perfect fit with the bottom of the pot. The sitter lifts the pot to safety out of the puddle of glaze that collects in the glaze catching bowl as the pot is firing. Crystalline glazes are extremely fluid at high temperatures, as you can see by the quantity of glaze that is in the catching bowl. After the firing, the pot must be separated from the sitter. I carefully work round the join with a hammer and chisel, and mostly have good success! The sitter is coated with a mixture of alumina and glue before the pot is placed on it, and the alumina acts as a release agent.
Pale, pretty crystals on this pot, overpowered by the dark brown runs from the tenmoko glaze that I used inside the pot and around the rim. With some colour combinations this can be very successful, but here the brown is too assertive.
The following two pots were in a firing I did whilst trying to do pots for an approaching exhibition deadline. The pots were very large, and I could just and so get both of them in my electric kiln with no room to spare for anything else.
Due to the large quantity of zinc oxide in crystalline glazes, usually about 25 percent, it makes things easier to calcine the zinc oxide prior to making the glaze. To calcine zinc oxide, you put it into bowls that have been previously bisque fired, and you heat it up to a red heat in the kiln. This process removes the chemically bound water that is in the zinc oxide, and it "pre shrinks" it. Without this treatment, zinc oxide shrinks a great deal in the early part of a firing, and can cause the glaze to crack up like a dry river bed, and parts of it may even fall off the pot. When I prepared the zinc for this glaze I slightly overheated it. The result was that it it made the glaze really difficult to sieve. I sieved for more than two hours, and finally managed to get the glaze to pass through a 60 mesh sieve. Mostly I use an 80 mesh for my crystalline glazes, and find that is quite adequate. Foolishly I gave up at 60 mesh, and assumed that the long firing and the fact that zinc oxide can be a strong flux, would be enough to break the zinc down further and make a working glaze.
A wiser course of action would have been to have calcined more zinc oxide (to a lower temperature), and made the glaze all over again.
The result of my bad decision and poor glaze preparation, was that the glaze formed a fascinating volcanic looking coating, that scarcely moved at all. You can see in the first pot with this glaze, that it stops half way down the pot. If it had behaved according to plan, the glaze would have run to the foot of the pot in great waterfalls! The other thing that went wrong was the under glaze that was put on the bottom half of the pot, this should have been a lacy looking chun glaze over a tenmoko. (blue-white over dark brown).
This was the other large pot that was in the same firing. Most of the lower two thirds were covered with the problem glaze. The top quarter had a regular crystalline glaze with some copper carbonate in. Sadly, I did not take the problem glaze right to the foot of this pot, as I assumed it would have found its way there easily by itself.
The last 5 hours of the firing I dripped cooking oil into the kiln as the kiln cooled from 850 to 700 Celsius (1562 - 1292 F). This gave me the spectacular copper red that you see in the top third of the pot. I have posted about this oil drip reduction process elsewhere.
If the under glaze had worked properly where you see it near the foot of the pot, or if I had glazed all the way to the foot with the problem glaze, I think this would have been one of my best pots ever.
Anyway, these few examples give you a little glimpse of some of the pots that have not quite worked out over the last month or so.
Whilst they can be a huge worry, very frustrating, financially damaging, and enormously disappointing, failed firings and failed pots are in fact to be welcomed, as they can be the best teachers of all! One very wise potter once said that there should be a failure in every firing, otherwise a potter is not making progress.
My experience of working with crystalline glazes tells me that in most firings there might be one really good pot, a few more that are OK, and about half of the pots that are not OK. Occasionally the whole kiln load may fail.
If something does not work, ask and answer the question "why" honestly, even if it makes you look or feel silly! Why is a good friend!
Finding the Good.
After a week or so to think about things, I am actually quite excited about the problem glaze. I hope I can reproduce it in future. I like the strange look of it and the texture. Used on an appropriate form, I think it could be stunningly successful! One thing to keep in mind about many of the "artistic" glazes that are used on sculpture or decorative pots, is that they were once glaze failures. Much admired "crackle" glazes may originally have been badly crazed glazes that were hopeless for domestic ware. The first crystalline glazes were problem glazes. I suspect that they occurred first when zinc oxide was being experimented with as a lower toxicity substitute for lead oxide in middle range glazes.
I think that the best way to cope with failure is to cultivate an enquiring mind!
Coming Exhibitions"Clay Works"
11- 26 May, Aigantighe Art Gallery, Timaru (opening function 10th May). This is the annual exhibition of South Canterbury Pottery Group. I was asked to be a guest potter at this exhibition and selector and Judge. Dunedin Ceramicist, John Paxie is the other guest potter.
"Bellamys at Five".
Laura and I will both be taking part in an unusual exhibition that will be held later in the year, from 2 - 22 September. It is an exhibition where poetry, painting, printmaking, and ceramics are all brought together in one place. There is a web site associated with the exhibition, and artists and writers that are taking part are being steadily added to the site.
Here is a link to the site. I sent some biographical material in recently, and Laura's will follow soon. Bellamys at Five.