Wednesday, May 13, 2009

Notes from a tool junkie: Firing PMC

Last week, I talked about my favorite tools for working in PMC, but there were so many, I only covered working with the wet and dry clay before firing. Today I will talk about tools I use for firing.

There are many firing options available for PMC, which is one of the things that makes it so accessible. It’s not necessary to have a special kiln for firing, although that option allows you to fire not only all types of PMC but also the newer Bronze and Copper Clays. The same kiln would also allow enameling, glass fusing and the annealing of glass beads. Most PMC kilns have controls that allow the artist to set the time and temperature and leave the kiln to do its magic.

There are many types of kilns available in a variety of sizes and price ranges. I do not have a kiln and have only used them in the classes I have taken so I will not go into depth here. A PMC kiln is on the top of my tool wish list, however. Kilns can run from about $400 upwards.

Because my budget hasn’t allowed me to get a kiln yet, I have tried some of the other alternatives: Ceramic Hot Pot, torch and the SpeedFire Cone System. I will discuss those below:

The Hot Pot is a small two-piece kiln alternative. The bottom contains a terracotta pot filled with an alcohol based gel, which burns for about 10 or 15 minutes. The Hot Pot is relatively inexpensive, but it’s hard to find the gel fuel. The other problems I found with it were that I had no idea at what temperature the Hot Pot is firing and the firing time was limited to the length of burn of the gel fuel. That amount of time will sinter PMC, but the pieces must be fairly small and thin. The short burn time limits you to firing only PMC3 and I have found that many pieces are simply not strong enough and are prone to cracking and breaking. I wouldn’t recommend this alternative. For the same money, or perhaps even less, a torch is a more viable alternative.

Torch firing can be accomplished with a small torch, like the ones used for crème brulée. They can range in price like anything else, but you can find them in kitchen stores, hardware stores and most stores and websites that sell PMC supplies for $30 or less. They take butane fuel, which is easy to find in hardware and kitchen stores. This is a great way to try out PMC if you don’t have access to a kiln. You will have much more control over the burning than with a Hot Pot.

If this is a firing method you would like to try and you already make jewelry, you may have a torch and supplies for soldering on hand already. When I torch fire, I use the same torch and setup I use for the simple silver soldering that I do. Other than the torch and fuel, you will need a fireproof surface on which to fire the PMC. I use a soldering board that is set on a turntable (handy for soldering, but not necessary for PMC) with a beehive board on top of it. A pair of tweezers is also helpful if you wish to pick up the PMC to quench it in water directly after soldering. I find that this is an excellent way to fire Aura 22 onto already-fired PMC and a great way to fire very small pieces. While you still don’t know the exact temperature of the torch firing, the color of the PMC will help you. If you have never fired with a torch, I would recommend the excellent written and video tutorials at the PMC Guild’s website, which you can find on this page: It takes a bit of practice to recognize the color stages of PMC as it is heated, so it makes sense to first practice a bit on scraps of PMC.

Currently, the method I use most for firing PMC is my SpeedFire Cone System. It is pictured here and is basically a modified campstove with a pyrometer. The cone, made of a fireproof material, concentrates the flame to bring the heat to the proper firing temperature. Any type of PMC can be fired on the SpeedFire. It uses the same propane fuel used in camp stoves, which can be found for about $2.00 in Wal-Mart. It screws right onto the bottle of propane or there is an adapter available so it can be hooked to a larger propane tank, like the ones used on gas grills. The SpeedFire Cone System is around $150.

I have experimented quite a bit with my SpeedFire Cone. The pyrometer is a big help. It’s probably not as accurate as one on a kiln, but it gives a good idea of firing temperature, so it’s easy to regulate. Just gently adjust the gas higher or lower to increase or decrease the temperature. It seems to hold its temperature well. The recommended firing time for PMC for optimum strength is two hours. I can get at least that much time out of one can of the propane. I am sure it would be even more economical to attach it to the larger propane tanks. When firing, I sit with the SpeedFire for a few minutes to monitor the temperature and then I use a kitchen timer to time the firing, checking on it occasionally. I use mine in the middle of my garage floor with plenty of clearance both around and above.

The SpeedFire Cone fires flat pieces well. I have also fired some round and domed pieces and they retained their shape. Traditionally, when kiln firing, most dimensional pieces are fired either in vermiculite or on a fireproof fiber blanket so that they retain their shape. I don’t know if this would work on the SpeedFire as the heat needs to surround the piece. I have used small bits of the blanket underneath corners and edges which has worked well. I have also fired Cubic Zirconia stones on the SpeedFire with no problems and organic cores seem to burn off just fine. If you intend to use one outdoors, choose a sheltered area. The flame is open enough that a good wind might interfere with firing.

The SpeedFire is also available in a mini version, which uses a refillable canister of butane fuel. I have not tried one. It appears to be quite a bit smaller than the regular SpeedFire and the specs say that the canister holds enough fuel for about 30 minutes of firing. There is no pyrometer. It runs about $90.

1 comment:

  1. Thanks for this information. I have no kiln and no idea how to fire domed pieces. I have UltraLite, it works good, but domed pieces become flat.

    Regards from Slovenia,


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