Brad Shute's Wicked Good

Question and Answer Page (4)
* Glass Furnaces *

Questions and answers about glassmaking furnaces.

* Updated June 11, 2007 *

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Following are questions I have been asked about glass, along with my answers to them. If you have glass questions, feel free to post them to my Glass Discussion Board. I regret that I no longer have time to answer questions individually via e-mail..

Q. I have heard of tank furnaces and pot furnaces. Can you explain the differences and also explain why you use the type you do.

A. This looks to be a full page question...

For studio use there are two primary types of furnaces which then divide into several subcategories per type. The types are tank furnaces and pot furnaces. The primary difference between a tank and a pot (also referred to as a crucible) furnace is the method of construction of the part which contains the molten glass.

Tank furnace

Pot furnace

Invested pot - Somewhat of a hybrid of a tank and pot furnace, refractory material fills the space between the pot and the backup insulation. This keeps the glass from leaking out if the pot cracks and provides some extra mass to keep the pot from cooling too fast and cracking in the first place. The pot will be useable longer because of this backup material, but when it does finally fail it is usually taken apart in the same manner as a tank furnace - with a sledgehammer. This furnace can take nearly as much abuse as (maybe more than) a tank furnace and melts better glass. This is what I built when I first opened my studio. Durable, easy to build, good glass quality, and energy efficient. This is what I would recommend for someone starting out, unless for some reason they needed a really large furnace. Then there isn't much choice other than a tank furnace.

All of these furnaces can be heated many different ways, but the most common in a studio situation is natural gas or propane, with electricity a distant third. As with the construction type, each has advantages and disadvantages. My first furnace was natural gas fired (the common choice, when available), and my current one (no pun intended) is electric, which I like very much. In an area where electric rates are not sky-high, I would personally ALWAYS build an electric furnace. (The fact that I have about 50 years worth of heating elements in stock doesn't hurt either.)

Some reasons I like electric furnaces:

Extended life of furnace materials and crucible due to even heating, no gas pressure fluctuations to worry about, simple and comparatively inexpensive safety system, no trips to the shop in the middle of the night to relight the furnace after a power failure (it restarts automatically), no flue necessary to vent combustion byproducts (and to waste heat), nearly idiotproof control system (depending on the creativity of the idiot), constant furnace atmosphere, and they won't blow up one's shop in the event of a disaster.

Last, and to me the most important - excellent glass quality.

There is more information about my electric furnace, including a crude wiring diagram of the control system, on this page. Questions about electric glass furnaces are also welcome on the discussion board of the website. There are many other people there who use, and/or have built, electric glass furnaces.

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