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Kiln Questions
by Tim McCreight [Studio PMC - 2004]
 
 

First, the “n” really is silent, at least according to the American Heritage Dictionary. There are kilns as big as your house, used for cooking everything from grain to stone, but we don't need to concern ourselves with those. Even in the sub-sub-category of benchtop electric kilns there are plenty of questions. Let's take a look at a few:

What are my options?
In descending order: programmable, pyrometer, and unregulated. The first option includes a device that monitors the power and turns it on and off as needed to maintain a specific heat. The second includes a device that measures the kiln's temperature and displays the temperature inside the kiln. You'll need to regulate the heat manually, but you can read the temperature and know what changes to make. In the last category are kilns without a temperature indicator. For these you use a separate pyrometer, temperature indicator pellets, or instinct.

Does the choice of kiln have anything to do with the type of PMC I'm using?
Sort of. A programmable kiln will handle any version with ease and confidence. If you are controlling the heat manually (option #2 above), the shorter firing times and various temperature goals of the newer versions of PMC make the process a lot easier. You could think of it like an archery target. Original PMC must be held at 1650°F for two hours. That's a small circle. PMC+ can be fired at temperatures ranging from 1470° to 1650°F and needs to soak for as little as 10 minutes. That makes it a bigger target. PMC3 can be fired at temps as low as 1110°F and is safe up to 1650°F.

What's the advantage of a programmable kiln?
A programmable kiln can read the temperature inside the kiln and adjust the power to maintain a consistent temperature. They can also be set to turn off at a particular time. The primary advantage of these features is convenience, since a programmable kiln will not require the same constant attention required by a manual or unregulated kiln. But it offers other advantages too, including more consistent results. Because the kiln maintains an even temperature, you can be sure that the fusing process has been optimal. In addition, some buildings experience electrical surges or spikes, so even a carefully watched manual kiln can jump to a high temperature unexpectedly and ruin a batch of work. The programmable kiln operates on heat, rather than current, so whether the heat rises gradually or on a spike, when the temperature gets to the desired setting, the power is immediately shut off.

Can I use the same kiln for pottery and PMC?
Ceramic kilns reach high enough temperatures to fire PMC, but most ceramic kilns are large enough that they have hot and cool zones. This variance is potentially too large to guarantee a successful PMC firing. That is, when the pyrometer reads 1650°F, some areas of the kiln chamber might be 1750°F, a temperature that will melt PMC. That said, the newer, more versatile versions of PMC are easier targets to hit, so ceramic kilns become more viable. The PMC will do no damage to the kiln.

Can I use a caster's burnout oven for PMC?
When PMC was first released, we recommended the Neycraft burnout oven as the most appropriate kiln available at the time. If you already have a burnout oven, you can use it for PMC. Again, there is no danger or maintenance issue in using the same kiln for both purposes. However, if you don't already have a burnout oven, a programmable kiln is only a little more money, and is well worth the investment.

Is one brand better than another?
I don't think so. Choose the features you want and can afford. Kilns with similar features are probably of equal merit, so make your choice based on the kiln's size and cost. The big difference you'll find is that some kilns are made of brick and others use a lightweight refractory foam. Aside from the weight, which only matters if you'll be moving your kiln around, the brick units take longer to reach temperature.

How dangerous are kilns?
Kilns are probably safer than toasters – first, because they are enclosed and second, because we don't take them for granted. Locate the kiln so it has at least 8 inches clearance all around and set a couple bricks or ceramic tiles in front to catch anything that might roll out. If there are children or pets in the area, take appropriate precautions.

How about maintenance and repair?
Kilns are really quite simple and consist of a heat-resistant box, a coil of metal that warms when electricity is passed through it, and a switch, in some cases a switch linked to a temperature reading device. If the "box" breaks, it can be mended with cement from a pottery supply. If the coil breaks (and this is uncommon) you'll need to contact the manufacturer for a replacement. The switch is probably the most fragile part of a kiln. In a simple unit you might be able to buy a replacement at the local hardware store. Replacement programmable devices can be purchased from the manufacturer and wired into a kiln pretty easily.

Can I work in PMC if I don't have a kiln?
Yes. One of the reasons the Mitsubishi scientists developed the ultra-dense PMC3 was to create a silver clay that would fuse at low temperatures in a short time. This opens the door to two unique opportunities – torch firing and Sterno furnaces. With a little practice anyone can use a jeweler’s torch to sinter PMC3
Other options include kilns you rig up from other heat sources, such as a jeweler’s torch.

If I can torch fire PMC, why should I buy a kiln?
Owning a kiln has changed my life. Okay, that's a bit overblown, but they are great things to have. I have used my PMC kiln to sinter all kinds of PMC, to fuse enamel, and to anneal metal. They can also be used to anneal glass, burnout flasks for casting, slump glass, and make dichroic glass. And if by some chance you find you don't use your kiln, they are easily resalable. The Guild web site offers a new feature called "Buy, Sell, Swap" where I often see people requesting used kilns.

How much do kilns cost?
The cheapest kiln I know of is the Ultralite, which sells for $130. There are a number of annealing kilns sold for glass work that come in around $400 to $450, and the programmable PMC kilns are running around $550.

   
 

 
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