BUTSER ANCIENT FARM ARCHIVE 1973-2007 Archivist Christine Shaw
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Butser Monograph:

The Discovery and Utilisation of Tin

the late A G Hamlin B.Sc.

SUMMARY

This work builds on the earlier studies, carried out by the author, on the production of copper, bronze, lead and iron.

Reasons are given as to why tin could, in principle, be readily produced using primitive smelting methods, provided relatively poor yields from an ore are accepted. The modern supporting concepts from thermodynamics are summarised.

A variety of approaches was explored in the use of a pottery kiln, a bowl furnace and a shaft furnace, to produce both tin and copper-tin bronzes.

In reality, production of tin proved more difficult than was expected and it was found that the discovery and utilisation of tin did not fit the system derived in earlier work for other metals.

The reasons behind this are discussed and the author indicates that tin bronzes may have been an easier use than the pure metal. The relationship of this to the juxtaposition of copper and tin ores in Cornwall, UK, a metal producing area of antiquity, is explored.

The bowl furnace proved most amenable to the preparation of both tin and copper-tin bronze (10%-20% tin). Initial indications were that, while a pottery kiln could be used successfully to produce copper-tin bronzes, the likelihood is that tin may not be readily discovered by this route. With the shaft furnace design in use at Butser, neither tin nor copper-tin bronze was produced but this does not preclude success using other designs.

[Summary written by Roger Hedge C.Eng.]

INTRODUCTION

The theory of the discovery and exploitation of metals developed at Butser Ancient Farm is based on the idea that the discoverers of metals were concerned with the production of pigments from the coloured ores of the metals of antiquity [1,2]. Pigments need to be very finely divided if they are to give good covering power. Manual grinding to this degree of fineness involves heavy labour, and the ideas developed at Butser assume that heat, applied by pottery kiln technology, would have been used as a means of breaking down the structure of the ore, either physically or chemically.

When a pottery kiln is working at maximum efficiency, the flue gases heating the ore are finely balanced between oxidising and reducing capability. If the conditions in the kiln stray from this maximum towards the reducing capability of the flue gases, for a sufficient length of time, metal rather than a finely divided ore will be formed.

Thus metals would inevitably have been discovered wherever ores were being processed to make pigments and there is no need to postulate a single source for their discovery and development, although the time scale for the realisation of the potential of the discoveries would depend on the perspicacity and skill of the processors.

Extensive experimental work at Butser Ancient Farm has verified that this theory is entirely tenable for many metals [1] and that it can be extended to explain why the reliable production of iron was delayed some thousand years compared with that of lead, copper, silver and lead-bronze.

However, tin does not fit this theory. Tin ore (cassiterite, tin dioxide) is dull brown to black in colour and although it gives a white streak on an abrasive surface, it would have been unlikely to attract much attention as a potential pigment. Moreover, the ore is sufficiently basic to react rapidly and completely with the ceramic material of crucibles, to form a glass, long before it reaches temperatures high enough to convert the ore to metal. It would therefore have been a non-starter in the pigment/pottery kiln theory of the discovery of metals and some other explanation for the appearance and use of tin must be found.