Fulford battlefied under threat

July 2014 dig

The Fulford Tapestry

Tuyères

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To achieve high temperatures for metalworking, air had to be forced into the furnace near its base through one, or sometimes more, small holes in the crucible that contained the charcoal. Their purpose was to protect the flammable materials of the bellows, made of wood and leather, from the heat of the furnace. These air inlets are often called tuyères, although recent literature refers to the holes in the furnace wall as ‘blowing holes’. This differentiates a separate, ceramic ‘donut’, histoRiccally called tuyères, from the blowing holes that lined the crucible.

“The fired clay material at Blue Bridge Lane includes a well-preserved tuyère (Find no 6233), which is vitrified on one side and oxidised on the other. The once-central hole has a diameter of about 15mm.”

The ceramic used has a high proportion of frit in the body which is of a white material. The frit, which is often ground particles of previously fired clay, is commonly incorporated in ceramic material which is designed to be subject to high temperatures. 

The use of wood ash for this purpose was mastered by Japanese craftsmen to produce their fine glazes. The flux lowers the melting point of the material with which it is intimately mixed, forming a glaze. Such glazing can be produced at temperatures as low as 800C.[i]

A close inspection of the ‘glaze’ on the fragments and the material suggests that we are dealing with different hearths. Their shapes also suggest that they formed parts of the hearth rather than the tuyères.

The interpretation that is placed on these fragments is that they are related to the other hearth objects by their location. All the material could be subject to laboratory examination when this area is fully investigated and a proper search organised. They might have formed a part of the equipment which was routinely carried on expeditions as the modern recreation below illustrates. In this example, soapstone[ii]  is used for tuyères, although no source for its use has been located.

These are three samples (of a total of 10) of coated material found close to the furnace bottom. The image on the right has a matt coating on a gritty ceramic base. The item on the right has a high glaze reminiscent of wood-glazes. The base material has a high content of frit. 
An example of a tuyères from the Lodese Museum store. It has a similar gritty ceramic base as those found at Fulford. However, there is no catalogue of these items making it difficult to draw any conclusions from the fragments found at Fulford.  

Tuyères and bellows: The use of twin bellows blasting air into the furnace is well demonstrated here. No part of the bellows touches the tuyères. Indeed, the gap has been shown by experiment to enhance the amount of air forced into the fire. In a personal conversation, the smith told of an attempt by 20 blacksmiths to weld items together and only 3 succeeded.

The successful hearths all employed two bellows and a gap to allow the blast from the bellows to draw even more air through the hole in the tuyères by the Venturi effect. Only with the enhanced temperatures achieved in hearths of this design did it prove possible to weld items together. As the interpretation attached to these furnace finds is that they were welding items together, one might expect to find other items displaying evidence of enhanced working temperatures.

 

 


[i] Bernard Leach A Potter’s Book – Faber 0571096727

[ii] Soapstone is a metamorphic rock, talc-schist rich in magnesium, produced by heat and pressure but without melting. It is common in Scandinavia.

 

 

There is a site devoted to saving the battlesite: The site has the story of the process that has allowed the site to be designated an access road to a Green Field, flood-plane housing estate. Visiting Fulford        Map York

And another website for the Fulford Tapestry that tells the story of the September 1066: This tells the story embroidered into the panels.

There is a blog covering these sites where you can leave questions and make comments.

The author of the content is Chas Jones - fulfordthing@gmail.com

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