Thursday, March 25, 2010

Two in the Morning and all that!

Oops... rather stuck together!

Well, it is two in the morning and I am waiting for a crystal glaze firing to finish before I go to bed. The pressure is on at the moment as I have an exhibition only 2 weeks away and have to get all the work glaze fired before then. I ran into problems in my last firing, and of the 11 small pots I fired, only 3 were OK, 2 were destroyed, and I am in the process of re-firing the rest as I write this.

I had odd mixture of things go wrong. Some problems I think were caused by firing the last few hundred degrees a little bit too slowly, which resulted in too few crystals in some pieces, but I had an odd thing happen to what had been a very reliable glaze in past firings where the copper colour came out a lot more blue green than previously, as if one of the glaze materials was a lot more alkaline than before. In fact the glaze looked quite different in character as well as in colour, so I have had to run a whole bunch of tests which I am firing now, to try to determine what caused the change. The cause could range from one of the glaze materials being from a newer bag, to the fact that the clay that the pots were made of was from a different batch than the ones before (and I have found that the clay body does have quite an influence on the glaze).

The most spectacular failure of all was the collapse of one of the little round insulating fire brick disks that one of the pots was sitting on in its glaze catching saucer. This was caused by the run off glaze penetrating through cracks in a coating of alumina that was on the fire brick, and simply eating away at most of the fire brick. I found that several of the other pots nearly suffered the same fate, and I was lucky to have not had a far worse disaster than I actually had. The pot that lent over very nearly came into contact with the kiln wall and the elements, and would have caused costly damage if it had touched them. It was a good reminder of what can go wrong. The break down of the alumina was most likely because I tried to economise by recycling some from the firing before, with the thought that the calcined alumina would in fact be more reliable as it would not shrink as much as the new stuff, but it obviously did not coat as well. We learn don't we!

Got one really lovely little glaze test out of the bad firing, and I am using that glaze on a slightly larger piece in this firing in the hopes that it will turn out well again.

Must go and shut off the kiln about now.

Thanks to all of you for your comments on the previous post. I will respond to them when I can open my eyes again! Laura appreciated all the nice things you said about her efforts too. Nice to hear from Joseph, a first time commenter. I also had an inquiry from Minna on one of my previous posts (about tiles and glazes). I have left a detailed response there, complete with glaze recipes for Minna as she asked for some advice and recipes for chun glazes.

2.30am Must go to bed,

Best Wishes to you All... P.

10 comments:

Armelle said...

Oh, Peter, I am so sorry for you, health and now pots problems !!!
It's often so in the life, problems series. You are probably right, simply a newer bag, and all is changed. I read and read again to understand glaze, and make tests again, but all could change with a newer bag !!!
What patience.
Best wishes

Tracey Broome said...

Testing is never ending! I'm making small things today to start testing some glaze recipes I found. Thanks to you for the white Raku glaze, I am much happier with it than the one I was using! One less test on that anyway:)

Pat - Arkansas said...

"I was all fired up, but needed a shoulder to lean on."

I'm sorry your glaze didn't turn out as expected; disappointing, I know. And, thank goodness the leaning pot chose its neighbor instead of the kiln wall. A small mercy, but a mercy nonetheless.

Hope you are able to rest a bit, even with the exhibition deadline approaching.

Peter said...

Bonjour Armelle,
Lovely to hear from you. Thanks for your sympathy. One good thing about a bad firing is that it is often very instructive. There are lessons to be had from glazes that run too much, craze badly, or are the wrong colour! Occasionally useful new glazes can be found this way too, so I am trying to keep an open mind and learn what I can, but I am just a bit scared by how little time there is before the exhibition!

Hi Tracey,
So pleased that the white Raku glaze is working for you, it is fun to think of it on two sides of the world at once and always interesting to see how glazes work in other kilns too.

Hello Pat,
Goodness, you must have only just sent your comment as I was reading the first ones, it is nice to think of you sitting there at your computer in Arkansas, and I am sending you a virtual smile and wave! I like the "all fired up..." quote, maybe the pot was just in need of a little comfort!

doug Fitch said...

Fingers crossed for you Peter. Jeff and Stella fly home tomorrow I think, I look forward to hearing all about the adventures they had with you

Peter said...

Thanks Doug, I'm a bit to tired to cross anything today, but it is nice to know that someone is on my behalf! Good to be reminded about Jeff and Stella being nearly home, time flies so and we are going to be sending a parcel to them... hadn't forgotten, but with all the activity here it would be easy to find that the day had come and gone! I'm wishing I could look into the kiln and see how the crystal glaze tests have gone, but 600 degrees is rather toooooo hot, so will have to wait for tomorrow. I'm really hoping something turns out OK this time, otherwise I had better leave the country in a hurry!

mudheartpottery said...

thanks for the nice comments on my blog. I didn't think you would be up and running today after your early morning kiln antics! I am sure your things will come out beautifully.
I'm afraid I am not doing nearly enough in the pottery area but I am happy with the porcelain so far. I am struggling finding time to sit and work but I need to be more disciplined. Little people do demand a lot of attention and they are totally irresistable!
Can't wait to see the latest kiln photos. (wearable art was a fun event - great video)

Linda Starr said...

sorry about the stuck pots, take er easy Peter

Peter said...

Thanks Linda,
Happy to report a much better firing this time... Yippeeee!

Peter said...

Lovely to hear from you too Lyn (mud heart pottery). Nice comments were well deserved, you do really great work up there in the North of Australia and it is always a treat to see what you are up to.