Twice-cooked travellers
Thanks Anitra, for the invitation to contribute. I have already learned a lot from you, and now Kriket as well - thanks to you both. My background is in glass and I am a newcomer to faience, so don't expect any expert advice here, probably more in the way of problems and questions...
Unfortunately I've had to be away from home a lot lately which has been frustrating... However, on the latest trip I decided to take it all with me. The first photo shows my tiny portable kiln and raw materials ready for the road.
I hadn't used this kiln before for temperatures higher than 540C (annealing glass beads) and I forgot to take with me the instructions for the controller. Searching online for those instructions led to an important discovery - that the top temp for this kiln is actually 920C not 1050C as I had thought... Would that be high enough for the paste? I had a go anyway and the results seemed OK, using Anitra's recipe of 16:4:2 (+ Cu Carbonate), firing the kiln at maximum for nearly an hour - but no pyrometer so not sure exactly what actual temperature. Just to see what would happen, on my return home I re-fired the pieces together with a new batch in my larger kiln, to 1000C. They don't appear any different after the 2nd firing... but at least don't seem to have suffered at all. Now I think I might try fusing two or more fired pieces - or adding detail with fresh paste to fired pieces to see if it's possible to build up more complex pieces in stages. Has anyone else tried doing this? I imagine the new bits will simply shrink and crack away from the old...The second picture shows some of the twice-cooked pieces.
Now a very basic question for those who have more experience of this material. The mushroom-shaped lump, top left, has thicker glaze on the right-hand side and it has also bubbled - looks quite nice, actually, though doesn't show up very well in the pic. Before firing it had a lot more of the salty efflorescence on that side than the other, possibly due to the sun shining on it as it dried. Anitra has mentioned size and position in kiln as factors affecting glaze thickness, but would I be right in assuming that uneven drying could lead to uneven wicking of the salts in the mix and thus to uneven glazing? Has anyone found out how to avoid this, or perhaps how to exploit it in interesting ways?Coming up... I'm wondering about making and using moulds (or is that "molds" with you?) for faience. Anyone out there with ideas or experience? I'm already messing around with the basic paste ingredients and an unusual glass-moulding technique, hoping to report back soon...
posted by ajda @ 8:21 AM
1 Comments:
Alan,
Thank you, for your post. I enjoyed it.
I'm back from my holiday at the Grand Canyon. Beautiful country, I wonder how it will show up in my work.
You bring up a lot of questions, some with no true "yes or no" answers. However, that is what this blog is all about.
Be aware that every great discovery is "1% inspiration and 99% perspiration". Understanding that glass so closely related to clay yet it has different fabrication techniques. Egyptian paste is certainly more glass then it is clay however, the addition of water makes it behaves more like clay.
Never attempted to join onto a previously fired work, this doesn't mean it cannot be done. It's just very difficult to compensate with the amount of shrinkage that occurs between wet to dry, and greenware to bisqueware. Perhaps I should explain that in ceramics unfired pieces that are bone dry are referred to as greenware; fired greenware is called bisqueware. We are on the frontiers of research here. So by all means try building on, perhaps we will discover something new. The results would certainly be a subject worth posting on. Carry on.
Being we are using the same recipe I can only assume the copper carbonate you are using is refined differently; it maybe just a difference in European copper mines. Your firings have accomplished something I've aimed at, but have yet to achieve. The tan, toasted color, on the underside of your piece is so close to artifacts found in ancient Egyptian burial sites. The underside of my works is generic white. Adding some iron oxide in is something I was planning of trying only after I have obtained the forms and control over this media that I desire.
Your traveling kiln is a fantastic research tool, as well as traveling companion. How do you like this kiln?
Yes, uneven drying will cause asymmetric efflorescence deposits. This in turn will give you additional glaze. However, bubbling you're experiencing is usually incomplete melting of the glaze. A longer soak time just might alleviate this. My experiences are with cones, rather than relying on a pryrometer, a cone relays the actual amount of work done by the heat. I'm truly amazed you can fire one hour. My smallest kiln is a cubic foot firing chamber and it takes nearly 3 hours to heat to cone 04 (approximately 1000°C). You may want to try a witness cone in your next firing.
Drying will always be somewhat uneven because of the shape of the pieces; the bottoms of pieces invariably have less glaze then the tops. You can obtain a additional even drying by going slow. Place a bucket or box over the pieces as they dry. Refrain from putting them in direct sunlight, unless you like that affect. You can use a wet box; that would be something like a Styrofoam cooler. I actually use a nonfunctioning refrigerator in my studio; it's ideal for slowly drying pieces.
Molds, moulds will be the subject of my next post. I use molds, but I appreciate your use of moulds. My wet box/refrigerator grows mold, but it's not the same, pun intended.
I eagerly await your next contribution.
------------------Anitra
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