Archaeology, Archaeology Research

pXRF of the Crosby Garrett Roman parade helmet

I posted previously that I would update after I had seen what is now being called the Crosby Garrett helmet.

In the end, I was asked not to by the Portable Antiquities Scheme with whom I was working, because of all of the uproar surrounding the helmet. On the day I travelled to see the helmet, I spent some time in the office of one of the PAS staff as they fielded calls regarding the helmet, and it was clearly politically sensitive, so I was happy not to make things any more difficult. However, it’s been over a year so I think I can now blog about the subject without any difficulty.

The analysis itself went well, although I only had thirty minutes with the object. The technique I used, x-ray fluorescence spectrometry, is non-invasive, so no samples were taken and the object was not damaged in any way. The downside of this is that the technique only examines the surface of the object, to a depth that (depending on material) may be as little as the width of a red blood cell.

As the surface of the helmet is covered in a grey-green-blue patina, probably a compact layer of copper oxides/sulphides etc., it is likely that the analyses I did would have been affected by this. That is to say, the numbers that the analytical machine generated are unlikely to accurately reflect the composition of the metal used to make the helmet. I’ve worked on similar objects with patinas/corrosion products before, and unfortunately its very difficult to judge how inaccurate the analyses are, as the conditions vary between objects.

I was able to confirm that the helmet is a copper alloy, as is the griffin finial, though this is probably no surprise to anyone. Despite the limitations of this analysis, I do believe that I can demonstrate that the griffin finial is of a slightly different alloy composition than the helmet. It’s not a large difference, but I suspect it relates to the different techniques used to manufacture the finial. The finial looks like it was cast and then worked by hand, which would call for an alloy tailored to casting, whereas the helmet would have required more complex manufacturing techniques that are outside my experience.

I hope at some point to publish the analyses, complete with a proper discussion of why the data is difficult to interpret and particularly why the numbers cannot be taken at face value. However my data were used by a number of publications during and after the sale of the helmet, so it remains to be seen whether I will be able to publish it myself in a more scientific format.

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