Thursday, April 30, 2009

Used Kilns - What to Ask

Should you purchase a used kiln for annealing your beads? Here's a few random thoughts on the topic.

A kiln is not really any more sophisticated than a well-insulated toaster oven. Sometime you see older kilns for sale - here's some questions to ask before you buy:

What what is designed for, and what has it been used for? A quick google may find that out for you. Ceramics kilns, kilns for enameling, etc, all can be used, with some caveats. Kilns for metal clay are relatively new - so unlikely to be too old or damaged. These may be sorta small - but they might work. Enamelling kilns may have some messy spills inside - but you can put a kiln shelf over it if you can't get the stuff out.

What voltage is it? 220 or 110. 110 is easy - 220 is faster to heat up and more efficient, but you have to have the plug for it (like a dryer plug.) Installing a 220 volt plug is non-trivial - it requires an electrician.

Are the elements encased? Bead kilns often have the heating elements in quartz tubes - this prevents you from touching them accidentally with metal mandrels. Metal mandrel on metal element is a bad thing. Alternately - the elements in a bead kiln may be recessed in the roof of the kiln where they are harder to stick a mandrel into. (But, not impossible. I know of someone who has done this.)

Top opening or front opening? A door on the front is nice - and if it has one - will it stay up by itself? Top opening - I know quite a few bead makers that prefer this. A pair of long tweezers helps a lot - put on the big suede welding gloves, grasp the mandrel below the bead with the tweezers, swing the door open (now you are losing heat) - pop the bead in, and swing it closed. You can practice with the kiln off and just mandrels!

How big is the inside of the kiln? Mandrels are often 9 inches or 12. Do you have enough room to get the mandrels in? Or, conversely - is it so big it is overkill? Heating that extra space will cost money.

How big is the outside of the kiln? You need space around it between it and the walls, etc. Do you have room for it? (Hint - if it takes more than one strong person to move it - it's probably overkill for beads.)

Is it old? It may be quite inefficient and leak heat through old, damaged firebricks or a poorly-fitting door. Ceramic fibre blanket can be replaced, however - especially around doors - where I think it is designed to be replaced on a regular basis. If the clips to hold this in place are missing - a couple of bent mandrels can replace them. Bend to shape. I use bent mandrels to repair all manner of things!

Are the elements in good shape? - not sagging or heavily corroded or kinked? Elements can be replaced - but they ain't free. Might be worth it though.

Is is controlled by a kiln-sitter? Ceramic kilns have a device that uses a cone melting at a specific temperature to shut off the kiln (called a kiln sitter) - a rather ingenious method of controlling the temperature but not accurate enough for glass. The usual protocol is to circumvent the cone sitter and install a pyrometer (a thermometer for high temperatures) to display the temperature and to manually control the temp with the control dial, or to install a digital controller. (Installing a digital controller is easy, btw. There is usually a hole in the kiln for the temperature probe. Pull this out - they aren't usually secured. Thread the one from the controller into the hold. Plug the kiln into the controller. Plug the controller into the wall. Turn the kiln to full. Set the controller. That's it. Done.)

If it's a very good price - it may be a good deal. (To me - I would want it to be under $200). Otherwise - kilns have come down a lot - and I do love having a digital controller! And a swing up bead door!

Of course - check out the cost of shipping if it isn't local - that may destroy any savings you were going to get!

1 comment:

  1. I really enjoy your blog and work on different glass.

    Just stopping by to let you know you have been tagged! :) Feel free to play or not, whatever you wish.