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24 July 2012

The Hoard Conservation Team Visit to the British Museum, 19-23 March 2012

As part of our continuing partnership with the British Museum (BM) the Metals Conservation Department at the BM hosted the hoard conservation team in March this year, for a week of information-sharing and discovery. The team at the BM have a great deal of experience working with Anglo-Saxon material and we wanted to learn more from them about the condition of the objects in their collection, conservation treatment approaches, and what changes they have seen in the objects over time. It was also a good opportunity for us to see a variety of objects dating from the same time period as the hoard but from different cultures and locations. For example, it was interesting to compare the hoard with cloisonné garnet work from the continent.

Curator Barry Ager showed us a variety of Anglo-Saxon objects in the collection, including a number of swords from sites across Britain (image 1.). Some of these swords were in remarkably good condition and the blade pattern welding was clearly visible. Many swords had lost their hilts and associated fittings, but a few had the hilts and fittings at least partially intact.

Image 1. The Sutton-Hoo Sword, British Museum image database

Conservators Marilyn Hockey, Fleur Shearman, Duygu Çamurcuoğlu and Ana Tam showed us a variety of objects from Ringlemere, an early Anglo-Saxon cemetery in Kent. Unlike the hoard, many of the Ringlemere objects were iron knives or copper alloy objects such as brooches and buckles, and many had preserved organic material such as textile attached to them. The team examined x-rays of some of these objects (images 2a and 2b) and it was interesting to see just how much additional decorative and manufacturing detail could be seen thanks to this method.

Image 2a. First x-ray

Image 2b. Second x-ray.
Images 2a and 2b. These x-ray plates show the same object at different stages of excavation from the soil block (these images are property of the British Museum).

The first x-radiography in image 2a shows the object in a block as it was found in the ground.  The block was so dense only the outline of the object is visible. Once the soil block was carefully excavated to reduce its thickness, a second x-ray was taken. This shows the beautiful detail on the object. On further examination the conservators discovered that the metal had completely mineralised and that the x-ray was the only way to view the beautiful decorated surface.

The team also spent a day with Fleur Sherman and Hayley Bullock, who took us to the Sutton Hoo reserve store and showed us a variety of shield bosses and other materials. It was fascinating to see these objects, much of which are still in fragments, in store. It makes one realise the research potential that still exists in the collection. Hayley also discussed her work researching shield bosses and handles. She talked through looking for organics (e.g., textiles that might suggest handles were wrapped), construction details such as rivets, and the thickness and layers of the shield itself, as evidenced by the metal remains. She has published a technical study in the British Museum Technical Research Bulletin, Vol 5 (2011), pp. 15-24.

The department of scientific research at the BM is well established: material testing such as chemical characterization and accelerated ageing to understand deterioration take place here. These are aimed at both informing the choice of display and storage solutions and at identifying historic materials.

Here the team had the opportunity to see some of the analytical equipment in operation and talk to some of the scientists who run analysis and interpret the results (image 3). These discussions were very useful in helping us understand the function and limitations of the different analytical methods. The hoard team has gathered several hundred samples, some of which are now being analysed at the BM using methods such as scanning electron microscopy (SEM), gas chromatography/mass spectrometry (GC/MS), x-ray diffraction (XRD), x-ray fluorescence (XRF), and Raman spectroscopy. The results of this analysis will help us better understand the materials, manufacture and use of hoard objects.

Image 3. Cym and Deb talking to Sue La Niece in relation to the use of the SEM. It is in the piece of equipment that some of the hilt plates will be examined in to see if there is organic material remaining within the soil residue.

In 2009 and in cooperation with the BM, a number of hoard objects containing garnets were analysed at the Louvre Museum in Paris using particle-induced x-ray emission (PIXE) (Images 4a and 4b). BM scientists are interpreting the data and producing a report of the results (to be published in 2013). These results will tie into the larger ‘Garnets Classical to Early Medieval (GCEM)’ project, which is looking at the physical and chemical characteristics of garnets from objects dating from 300 BC – 700 AD.

Image 4a. The PIXE equipment

Image 4b. The PIXE equipment and the beam being lined up on one of the garnets in the Hoard.

In addition to hoard-related activities the team also met with metals conservators and learned about their recent or current projects. Jamie Hood and Alex Baldwin showed us the incredible Chiseldon cauldrons (images 5a and 5b.), a prehistoric hoard (ritual deposit) of 12-13 copper alloy cauldrons. See the BM’s blog about the cauldrons: http://blog.britishmuseum.org/category/archaeology/chiseldon-cauldrons/.

Image 5a. Cym examining the cauldrons in the studios at the BM

Image 5b. Part of a cauldron

Marilyn Hockey talked to us about the conservation of the Hallaton Helmet (http://blog.britishmuseum.org/tag/hallaton-treasure/), a 10-year project to reconstruct a highly fragmentary Roman iron helmet with silver overlay.

Image 6. The highly fragmented Snettisham helmet

Another of the challenging conservation projects at the BM: the highly fragmented and corroded Snettisham helmet. This puts the poor state of conservation of some of the Staffordshire Hoard objects into perspective. The team were reminded that when conserving objects such as these helmets,  the mounting and display solutions ought to take into consideration their extreme fragility and that safe, practical strategies be devised for the purpose.  The conservator is called upon not only to provide solutions to achieve the stability of an object, but also to contribute to the interpretation of each individual piece or fragment, in order to create a coherent, authentic and ethical reconstruction.

One of the areas of interest was understanding how silver objects deteriorate under archaeological conditions and what surface finish one can expect to see on a silver object and how fragile the silver structure becomes.

These images show how the silver can become denatured. The surface becomes dull, rougher and more crystalline. The image at the bottom shows all that remains of a deteriorated silver bowl. The remaining parts being so fragile that they are supported on Perspex mount. This not only supports the fragile pieces of silver but remove the need to handle the fragile objects.

The week spent at the BM was very educational and worthwhile, and we would like to thank our hosts for making the week so informative and fun and for providing information that will be useful to us in conserving the hoard.

 

Deborah Cane, Cymbeline Storey, and Deborah Magnoler

The Hoard Conservation Team
Birmingham Museum & Art Gallery