{"id":128,"date":"2010-03-01T16:35:08","date_gmt":"2010-03-01T16:35:08","guid":{"rendered":"http:\/\/primitive.userblogs.ganoksin.coms\/?p=128"},"modified":"2010-03-01T16:35:08","modified_gmt":"2010-03-01T16:35:08","slug":"planning-for-a-rudimentary-furnace","status":"publish","type":"post","link":"http:\/\/userblogs.ganoksin.com\/primitive\/2010\/03\/01\/planning-for-a-rudimentary-furnace\/","title":{"rendered":"Planning for a Rudimentary Furnace"},"content":{"rendered":"

The aim is to build a small outdoor furnace, constructed primarily from unfired clay, and fueled bycharcoal. The furnace needs to be able to achieve melting temperatures for sterling silver, so in the region of 900C. Failing that, the furnace needs to achieve about 650C for the purposes of annealing. Eventually, I’ll try to replicate specific designs of Viking and middle age furnaces, but for now, I want to work with the basic principles.<\/p>\n

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At a later date, my intention is to try different fuels. I’ve already discussed this here<\/a>.<\/p>\n

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I’ve started making enquiries about buying clay – if anyone has any advice please post a comment. Because of the kind of fires that I’ll be working with, it looks like earthenware crucibles are the most likely items for me to produce – they are fairly porous, and need lower temperatures than other clays to produce – I’m not intending on achieving temperatures high enough to make other kinds of pottery, and the methods I’ll be using will likely be limited to crude pit-firing. I’m hoping that I can use the same clay for both tasks.<\/p>\n

\"Initial<\/a>
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The initial site will be a disused flower bed in my garden – I can pack the soil into a slope, and build into it. The pit will be lined with unfired clay, or perhaps a layer of sawdust and then clay – I have a feeling that soil might prove a poor insulator. It might be possible to face the firepit with clay, leaving a hole on top, (to rest the crucible in), and a hole at the bottom front for the tuyere pipe to enter. It may be necessary to provide a lid of some sort to reduce heat-loss through the top.<\/p>\n

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From what I’ve read, the basic structural requirements are a refractory (or heat-proof) material, an insulating material surrounding that, and a protected area for the tuyere pipe to blow air into the fuel. Apparently, tuyere pipes can be damaged by extreme heat, and can be blocked by dirt, fuel, metals and residues, so the pipe needs protecting, while still injecting air as close to the centre of the furnace as possible. This might be achieved by placing several rocks or clay lumps around the end of the pipe, to stop objects falling directly into it. I’m intending to use a pipe that angles down into the furnace, ideally driven by bellows.<\/p>\n

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Beyond the basic materials to create heat, I’ll also need a few other items, which I’ll discuss in detail elsewhere.<\/p>\n