How to fire up a bloomery fur­nace

Buckinghamshire Advertiser - - LIFE & LEISURE - To find out more about the Iron Age and our Iron Age School work­shops visit www.coam.org.uk. PEARCE, COAM ED­U­CA­TION AS­SIS­TANT

man­u­fac­ture and met­al­lurgy. At the Chiltern Open Air Mu­seum (COAM, we have re­con­structed an Iron Age bloomery fur­nace based on re­search from ex­per­i­men­tal ar­chae­ol­ogy, ex­ca­va­tions and the help of Jack Greene, his­tor­i­cal ed­u­ca­tor.

Iron smelt­ing is a com­plex process re­quir­ing huge amounts of heat. We ex­tract iron from ores which are min­er­als con­tain­ing iron. The bloomery method of smelt­ing does not melt the iron, but in­stead, the tiny par­ti­cles of iron stick to­gether, sep­a­rat­ing from the min­eral and form­ing a ‘bloom’. The waste ma­te­rial (the slag) falls to the bot­tom of the fur­nace.

The fur­nace is a cone shape with a cir­cu­lar shaft run­ning down the mid­dle and is made of a ma­te­rial called daub. Daub is a mix­ture con­sist­ing of a clay and wa­ter slurry, straw, soil and horse ma­nure (fresh from our shire horses). The Daub is stuck onto a cir­cu­lar wat­tled frame, with a hole left for the ‘tuyere’ to al­low bel­lows to be at­tached.

Once the struc­ture is dry (which usu­ally takes a day) the leather and bone bel­lows, can be at­tached.

A fire is started in the bot­tom of the struc­ture and when well alight, the forge is filled half way with char­coal topped by crushed iron ore. The rest of the fur­nace is filled with char­coal. Bel­lows achieve the high tem­per­a­tures needed to smelt iron. The fur­nace is then bro­ken open to ex­tract the iron.

TOM

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