English: A collection of metal working debris dating to the modern period. The debris consists of approximately 18 pieces of metal and four fragments of crucible, all of various shapes and sizes. The metal itself is mostly brass, some of which has iron, tin, lead and nickel components. There is a zinc ingot as well as gunmetal and other alloy fragments. The crucible fragments are highly vitrified. The collection was submitted to Oxford Materials for analysis. The FLO is indebted to Dr Peter Northover and Dr Brian Gilmour for their time, expertise and analysis of the material. The report and analytical results written by Dr Peter Northover follows below.

Analysis of metallurgical debris from 'Witney area'

A metal detector find of a small collection of semi-finished products such as bar, and metalworking waste, from near Cogges was submitted for metallurgical analysis. A selection of the material was analysed by X-ray fluorescence analysis with energy dispersive X-ray spectrometry. The writer is indebted to Dr. Brian Gilmour for assistance with these analyses.

The data from 13 pieces [was analysed]. In all cases there was a variable amount of iron in the analysis from the environment with the exception of some of the brasses which had been cleaned and could contain iron as an impurity.

Five of the pieces can be described as brasses. One is yellow brass with a measured 32.3% zinc; when brass is melted zinc is lost to the vapour phase and the original zinc content of this brass would have been about 34%. The composition is typical of a number of modern brasses which can also contain minor additions of other elements not measured here (for example aluminium).

Four more brasses have around 29% zinc and are also alloyed with varying amounts of tin and lead to improve strength and mechanical properties. The nickel impurity in three examples is typical of brasses made at the end of the 19th century and for much of the 20th century. The fourth in this group, with 18.9% zinc, could be scrap of a little earlier vintage.

One piece, with 8% zinc and 6% tin could be described as gun metal, but might rather be the result of mixing a variety of copper alloy scrap, together with some copper. The other two mixed compositions, with low zinc and tin, have roughly the composition of pre-decimalisation bronze ("copper") UK coinage. Somebody might have been melting down a sack of old pennies. In the table there follows a bronze, possibly a modern phosphor bronze; the zinc could come from contamination from the crucible the melter was using.

There are two pieces of zinc, one more or less pure, the other containing percentages of copper, tin, and lead, again probably the product of rather mixed re-cycling. The final two pieces are of lead and a white metal which is probably either type metal or a bearing metal.

Although, in theory, these alloys could have been made at any time in the last two or three centuries, the condition of some of the pieces, the nickel impurity in the brass, and the potential use of coinage metal, combine to suggest a 20th or even 21st century date for the activity at Cogges.