The aim of this analysis has been to identify the metal that the shroud pins associated with SK[2] were made from. The original assessment of the shroud pins (Baker and Baker 2007) suggested that the pins were possibly gold, or gold-plated, and it was recommended that the pins were examined and, if required, analysed by an archaeometallurgist.
To determine the type of metal that the pins were made from, it was felt that the least destructive method of analysis would be X-ray fluorescence (XRF). In XRF, a beam of X-rays is directed onto the surface of an object, which then emits an X-ray spectrum. The spectrum contains peaks for each element present and this information is used to calculate the relative amount of each element present. XRF is a commonly used method of chemical analysis in archaeology and it can be used as a non-destructive technique (English Heritage 2001).
The main limitation of XRF is that, used non-destructively, it can only analyse the surface layer of an object, which may not reflect its true overall composition. To overcome this limitation it is normal practice to analyse the surface and then remove a small amount of material from the object to allow analysis of the sub-surface.
Surface XRF analysis was performed on one of the pins. The surface of a section of the pin was then ground away to reveal clean sub-surface metal. The results of the XRF analysis are shown in Table 4.
The results show that the pin is made from brass and that it is not plated. The difference in composition between the surface and sub-surface is as expected from 'weathered' brass.
It may be worth noting that the particular ratio of elements present is typical of brass used for the manufacture of thin wire and pins. Coincidentally, this particular type of brass was/is colloquially described as 'yellow brass', because of its golden colour (Overman 1852, 683).
The pin analysed is typical of those recovered and the results are very likely to be representative of all the pins. The fact that the type of brass used for the pins was known for its gold colour may just be a coincidence, rather than deliberate choice, as this particular alloy was the most suitable for drawing into fine wire.
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| File last updated: Wed Jan 19 2011