Tuyere and Bellows

by Jamie Hall on March 15, 2010

The evidence for most of this comes from De diversibus artibus by Theophilus. A copy of the text, in English and Latin, is available here. Most of it has alternating pages of Latin and English – with a little ingenuity, I’ve managed to print the English portion of the book. The pages suit A5, or two pages on a landscape A4 sheet. Only the latter third relates to jewellery, so not all of the book needs printing. In addition to the translation, there are notes in English, but they sadly don’t cover all of the text. Note that the translation was published in 1847.

The function of the tuyere is to provide a focused supply of air into a furnace. The air is usually provided by a motorised pump in the modern world, but in the past it had to be done by bellows or human lungs. Both approaches will be tried, but lungs alone are likely to be a difficult way to do it. Interestingly, Theophilus seems to refer the use of bellows so that the “furnace may become dry”. I assume that this was his interpretation of the effect on oxygen on fire.

When the tuyere is commonly discussed, it’s in a blacksmithing or smelting context – the furnace needs a powerful blast of air for many hours for the work to be completed. However, I don’t need a large furnace, and nor do I need to keep it at maximum heat for a long time – I’ll mainly be annealing, soldering and melting small amounts of silver, so I hope that bursts of 15 mins or so will be enough to achieve that. The rest of the time, the furnace will be burning, but at a low heat – this should also reduce my fuel consumption, which would otherwise require a very large mass of charcoal.

The pipe must be able to withstand considerable heat – the hottest part of the furnace will be that which has the most oxygen, and that means the end of the tuyere. An iron pipe seems like the simplest solution, but how easily would that be formed, and how authentic would that be to the middle ages? Some discussions of historical pipes usually refer to ceramic tuyeres – these could be made using the lost wax process, which would give them a very regular form, and a corresponding strength. At a later date, I might source or make a ceramic tuyere.

There isn’t much detail on pipes in De diversibus artibus, but Chapter IV describes bellows made from a whole ram’s skin, cut down the spine, and mentions that the head of the bellows has a hole for an iron tube – this must be the tuyere pipe, that carries air into the furnace. It’s good to have documentary evidence that iron was used for this purpose. I expect that the tuyere will be damaged by exposure to the furnace, though not as badly as it would from the heat from a blacksmith’s forge.

The bellows themselves are hard to work out from the description. Based on the way bellows were made in more recent history, the top and bottom of the bellows are made rigid with handled boards, which are hinged at the head of the bellows, where the pipe come out. A whole ram’s skin, cured and stretched, would be quite large, so I should be able to use something smaller and simpler. With a very small furnace, I might be in danger of providing too much air, and making the atmosphere more oxidating, if I have large bellows. This page on primitive blacksmithing has a diagram (fig 1) made of two small skins, and may use the same principles.

Anders Söderberg, here, describes a pair of bellows used with two hands to provide a regular airflow. I’ve read elsewhere that continuous airflow is more important than fast airflow. The easiest way to replicate this style of bellows will be with two bellows connected together. I expect that I’ll buy some on ebay, or check out car boot sales and charity shops. It might even be easier to make some.


P eter Bond March 15, 2010 at 13:09

If you have a look at “Basic Blacksmithing: An Introduction to Toolmaking”, there’s a lot of low-tech solutions to building forges & bellows.

As for the tuyere, a simple clay pipe works – as with the moulds, it may be worth tempering it with some sand (or grog if you have any); in a pinch, a chunk of scaffold pipe works. just be sure a) it isn’t galvanised – breathing zinc fumes is hazardous – and b) it isn’t aluminium…

Jamie Hall March 15, 2010 at 18:59

I’ll have a look at that book. I’m planning on getting some offcuts of iron or steel pipe from the local steel merchant.

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