X-ray vision sheds light on the Staffordshire Hoard story

By on 04/08/2011 in Culture, News

Conservation experts are employing 21st Century techniques to shed light on the origins of a hoard of 1,400-year-old Anglo-Saxon gold.

Conservators at Birmingham Museum and Art Gallery (BMAG) are using state-of-the-art X-ray Fluorescence (XRF) as they piece together the story of the Staffordshire Hoard.

The technique will enable experts to analyse the exact metallic composition of more than 3,500 artefacts that make up the largest hoard of Anglo-Saxon gold ever found.

Through XRF curators have discovered some Hoard artefacts contain 94 per cent gold (around 22 carats). This is far higher than most modern jewellery, and as gold is very soft unless it is alloyed with other metals, may explain why some objects are very worn in places.

BMAG curator David Symons said: “Experts are currently piecing together the fascinating story of the Hoard and through this technique we can understand so much more about this magnificent find.

“X-ray Fluorescence has added to our growing knowledge of the Hoard, making it possible to carry out detailed and accurate analysis of the composition of artefacts - something that would have been much more difficult in the past.”

Graeme McArthur, Intern for the Hoard Conservation Team at BMAG, recently analysed two hoard objects using XRF. His findings can be seen below.

K353 Gold Pommel

K353 Gold Pommel

The object shown above is the pommel of a sword or knife, a pommel is the part found at the very end of the handle. This pommel has been decorated with twisted wires in a technique known as filigree. The bright yellow colour of the metal suggested that it was very pure gold with little silver or copper present that can make it slightly pink or white. Analysis showed this to be the case with a large gold (Au) peak present on the spectrum shown below in fig. 2 and only very small peaks for copper (Cu) and silver (Ag). The result given was 94% gold which is around 22 carats. This is far higher than is usually used in most modern jewellery as gold is very soft unless it is alloyed with other metals. This may explain why the surface of this object is very worn in places.

XRF spectrum for the surface of K353

XRF spectrum for the surface of K353

The object shown below is a decorative silver edging that would have been riveted to a larger object. It is inlaid with a substance known as niello; a compound containing silver and/or copper and sulphur. It has also been gilded along the left side.

K64 Silver Edging

K64 Silver Edging

The spectrum produced on the silver surface inlaid with niello shown below indicates that the surface is mostly silver as would be expected. Although sulphur will be present as part of the niello it is unlikely to appear on this spectrum as it is a light element which produces low amounts of energy which may be absorbed before it reaches the XRF's detector. 

XRF spectrum for the silver surface of K64

XRF spectrum for the silver surface of K64

ENDS

NOTES FOR EDITORS

Photographs are available to download from: http://www.flickr.com/photos/birminghamnewsroom/sets/72157627353916208/

For further details about the Staffordshire Hoard conservation work go to: http://www.staffordshirehoard.org.uk/

Conservators currently working on the Hoard conservation are available for interview.

For more information contact Geoff Coleman on 0121 303 3501

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