Tuesday, November 27, 2012

My kilns

 To make lampwork beads that will last, they must be annealed in a kiln. Most bead kilns have a bead door that you can open and insert your beads still on their mandrels, which is ideal. Think about what you are going to use your kiln for most of the time and buy the kiln based on that need. I am a fan of buying a kiln for beads and a different one for fusing or PMC. Sometimes trying to get one that will do all these things results in none of them being done well.

Think about whether you want (or need) a digital controller. They raise the cost considerably, but are very helpful in following your annealing schedule. For beads, the firing schedule is relatively simple, but for complicated schedules for fusing or casting glass, a digital controller makes it much easier. If you happen to come across a really good deal on a bead kiln that doesn't have a digital controller, you can buy one and install it yourself, which is usually pretty simple.  An important consideration is the electric requirement. Most bead kilns can be simply plugged into a household outlet, but larger kilns may need a dedicated 200 amp outlet, so be sure to check the requirement of any kiln you are considering. Generally, the bigger the kiln, the more amps it requires to operate.

Another consideration is the type of insulation in the kiln. Ones built with firebrick (these look sort of like white bricks) will take longer to heat up to your working temperature, and then will take longer to cool down to room temperature- not necessarily a bad thing. A kiln lined with fiber blanket heats up and cools off much faster. It cools off fast enough that usually you must fire down (control the heat when coming down to room temps) or your beads can crack. Many firebrick kilns cool off slow enough that they can simply be turned off after an initial soak. A firebrick kiln is more fragile and not very portable. Usually you set them up and leave them there. Most of the toolbox type kilns use fiber blanket, making them much lighter and easy to carry around. These are ideal for beads, since you can easily put your beads in the kiln with the mandrels sticking out, but they don't work too well for fusing or PMC. After a lot of use, the fiber blanket will get mashed down and may need replaced at some point. I have one I have used for over 10 years, and while the blanket is much thinner than it was originally, it still does its job just fine.

My first kiln was a large one I used for fusing glass. It is a top loading kiln with elements in the sides and top and has a 36” diameter. I tried using this to anneal my beads, but it didn't work because the kiln lost too much heat every time I opened the door to put a bead in. I could have used it for batch annealing- making a bead, putting it in vermiculite or fiber blanket to slow down its cooling, and then putting the room temperature beads in the kiln and running a schedule. But there was a risk of beads cracking, so I bought my first toolbox kiln from Don McKinny, pictured at the top.  Unfortunately he no longer makes them- it is my favorite kiln, hands down! It is for annealing beads only, but I can get piles of beads in it. 

Then I decided I wanted to try some casting, and I found a great deal on a firebrick kiln that was for beads also. I thought that was a good idea- I would have a back-up kiln for beads in case my toolbox kiln went down. There was no digital controller on that kiln so I bought that separately. I simply stuck the probe in the peephole in the kiln, and programmed some schedules into the box. However I was having some beads crack, and it finally occurred to me that the probe reading the temps was 6-8 inches above the floor of the kiln. Since heat rises, I thought maybe the floor of the kiln was too cool, and sure enough, the floor of the kiln was 100 degrees cooler! So I added 100 to the numbers in the firing schedule, and then it worked fine.

 The most common problem with kilns is the elements burning out, and if you are at all handy, they are not difficult to replace yourself. Don't fire your kiln over the temperature it is rated for, because that greatly shortens the life of the elements. With a little care, your kiln will work for many years!

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