FEBRUARY 26TH 2016 - Coin Hoard Blog - Jersey Heritage

My colleague Viki and I went to Birmingham Museum and Art Gallery last week. Pieta Greaves, one of their conservators had invited us over so we could X ray our gold jewellery with their high resolution equipment.

This went really well and we get better images on all the pieces than we'd seen until now.  It confirmed some of our ideas about them and also presented us with a few surprises.  One surprise (which I should have known if I read more about the hollow torques from the Snettisham hoard in England) is that the bulk of each torque was made of a hoop of wood fitted around an iron rod.  The X rays showed the 4-5mm iron rod at the torques' centers but they also showed the grain of the wood surrounding these, now preserved by the corroding iron. 

The X rays also showed that most of the torques had a very simple join at the "double ring" end, worn at the throat.  We had been expecting a T bar and slot join but in fact most of them just have the plain gold tube of one half slotting into a hole within the other buffer side half.

The real bonus of the trip however was that we were given access to an X ray fluorescence spectrometer which for the first time allowed us to determine exactly what the composition of the metals in the jewellery surfaces was.  It turned out to be much higher than we had expected, pretty consistently between 95 and 97% gold.  This means that they are about as pure gold as could be made, essentially twenty four carat.  We also checked the results between gold that we had cleaned and gold we hadn't and were relieved to find that the  treatment we use does not appear to affect the results.  Whether these results are correct for the whole thickness of the gold is not definite yet as there is a possibility that the Celts used a surface enrichment technique to remove impurities from the surfaces.  Hopefully we'll answer this later.  The X ray spectrometer also revealed that the red, resin-like material coming out of the open end of one torc was in fact just iron corrosion and not an organic compound at all.

I'll have to sign off now as I'm in a mad rush but I'll write again next week.  Finally, a big thank you to Pieta and all of the staff at Birmingham Museum and Gallery for all their help and patience while we were over there as it was just great.  PS. Staffordshire hoard, blimey!