Friday, February 25, 2011
Thursday, February 24, 2011
This week I received notice from the Marion Arts Festival that I have not been accepted to be a vendor at the festival. This is my first rejection notice for summer art fairs, and probably not the last. There's a lot of competition out there! The Marion fair had over 350 applications and only accepted 50 artists. Only 20 of those were first time vendors at their fair, so I guess I can't feel too bad with those odds. I've already applied to some other fairs, so keep your fingers crossed for me!
Thursday, February 17, 2011
There are a lot of recipes out there for kiln wash, so I thought I would share mine with you, along with an explanation of how I arrived at the formula. For those of you who are not kiln-savvy, kiln wash is a refractory (able to withstand high temperatures) material that we put on kiln shelves for two reasons:
- It keeps pots from sticking to the shelves during firings. This isn't usually an issue with low fire pots, but with mid range and high fire pots our clay bodies get close enough to their melting points that the clay becomes just a bit tacky at peak temperature and will stick to the shelves a little bit. When you take them out of the kiln, little pieces of the pots will get plucked off where they have stuck to the shelf.
- It provides a protective layer in case a glaze runs off a pot and onto the shelf during a firing. While it won't always keep the glaze from sticking to the shelf, it does keep it from soaking in as much, and makes it easier to chisel the glaze off.
Two things are needed to make a good kiln wash: refractory material and some clay. Most people use alumina hydrate (or oxide) or flint (silica) or both for the refractory material. I like to use both. I find that alumina works better, but it is much more expensive that flint. The combination is a nice mix of functionality and affordability. The clay is necessary to hold the alumina and silica together and make it easier to brush onto the shelves. For the clay portion of the mix I use EPK (Edgar Plastic Kaolin), just like everybody else, although any kaolin will work. Kaolin is fairly refractory for a clay, and it has no iron impurities that could affect the performance of the wash in reduction firings.
My wash recipe started out as equal parts alumina hydrate, flint and EPK, but I found that it was flaking off after a couple of firings. This is a major problem because those flakes could fall off the shelf and land on a pot. The reason it was flaking was that is was shrinking too much. As it shrunk it pulled loose from the shelf. Specifically, the kaolin was shrinking too much.
So how do we get the kaolin to shrink less? Calcine it! Calcining is simply firing the raw material before using it in the mix, therefore pre-shrinking it. I just put a bunch of EPK in a bowl and run it through a bisque firing to accomplish this. You can buy calcined kaolin, but it costs a lot more.
I mixed up a test batch using calcined kaolin, and it just wouldn't apply to the shelves right. Once the kaolin is calcined, it doesn't behave like regular kaolin. So I tried half and half, which worked great. It applies nicely, and lasts many firings. My final recipe:
Alumina Hydrate 33%
Calcined Kaolin 17%
Add water and mix up to a pancake batter consistency. Apply 3 coats to kiln shelf.
Friday, February 11, 2011
So here's what happens when something goes wrong with a Kiln Sitter and the kiln over-fires:
The green gunk coating the now potato-chip shaped shelves and the bottom of the kiln is what's left of the pots that were in the kiln. That's right, the pots melted. I'm not exactly sure what caused this to happen on this kiln. It's typically caused by the cone sticking to the sitter rod, and we find a melted cone running down from the sitter tube, but there wasn't one in this kiln. There was no evidence of cone being in the sitter at all. Plus the shelves were laying in a pile at the bottom of the kiln, which is odd. Usually the shelves are still stacked. My best guess is that for some unknown reason the shelves shifted and bumped into the sitter tube, knocking out the cone but lodging against the sitter rod, thus preventing the sitter from shutting off the kiln. Once the kiln got hot enough to warp the shelves, the shelf blocking the sitter rod fell to the bottom of the kiln and the sitter shut off the power to the kiln. The big question is why the timer didn't shut it down. It could be that it was set too high, or it malfunctioned. It seemed to be working fine when I checked it, but it is a very old timer and could be sticking. The only way to know is to let it run a few times and see if it's working properly.
So the owner of the kiln has a decision to make: fix it or replace it. Due to the age of the kiln, I'm going to recommend replacing it. Fixing it will require a new floor slab, 4 new elements, 17 wall bricks, and 3-5 hours of labor. Ideally, we should also replace the timer. It's time for a new kiln!
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I received notice that I have been accepted as a vendor at the Cambridge Pottery Festival in Wisconsin! This should be a very fun show. Nothing but potters selling pots, making pots, and talking about pots. This festival is also home to the U.S. Pottery Games, with many pottery making competitions that test speed and skill. If I can find someone to watch my booth, I am going to enter the competition and see how I stack up against other potters. This year's festival is on Saturday, June 11th & Sunday, June 12th. Come up and join the fun!