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27 July 2012

Using Thorns to Conserve the Hoard

One of the challenges we face in conserving hoard objects is the softness of the metal, especially the gold. Many hoard objects have a high gold content (there is a wide range but 60–80% gold is seen frequently), and gold is a particularly soft metal that can be scratched easily.

Steel implements such as scalpels, picks and pins are commonly seen in a conservator’s toolkit, but these tools are harder than the hoard objects and are therefore not ideal for cleaning objects because of the high risk of scratching.

Many hoard objects already have a number of surface scratches, but these are the result of use, burial or excavation (see Figure 1). We have also encountered a number of deliberate scratches on the objects that we are interpreting as ‘laying-out marks’ or marks made by the Anglo-Saxon craftsman during the manufacture of the object (see Figure 2).

Surface scratches typical of those seen on many hoard objects.

Figure 1. Surface scratches typical of those seen on many hoard objects. These marks were likely made during use or burial and are part of the object’s history.

Bottom of K1003 showing the deliberate marks in the gold on the bottom and left sides.

Figure 2. Bottom of K1003. Note the deliberate marks in the gold on the bottom and left sides. These marks made by the maker of the object add unique a human touch to the object and may give us information about the maker’s tools and techniques.

All of these marks on the objects are part of their history. The last thing we want to do is add new scratches to the objects during conservation. As such, we have had to find a conservation tool that enables us to do our job in the safest possible way for the objects. The solution, originally suggested by Hoard Conservation Manager Deborah Cane, is using natural thorns to clean hoard objects.

Thorns have the additional advantage of having very fine, flexible points that can get into very small areas. Many hoard objects have very fine cloisonné or filigree decoration, and a tiny implement is required to remove soil around these decorative features (see Figure 3).

Using a berberis thorn in a pin vice to remove soil from a gold hilt collar with cloisonné garnet decoration

Figure 3. Using a berberis thorn in a pin vice to remove soil from a gold hilt collar with cloisonné garnet decoration.

Thorns from several species of plant were trialled, but the thorns that had the properties we were looking for—softness, flexibility, and thin/small size—were berberis, pyrocanthus, hawthorn and blackthorn (see Figures 4 and 5). These thorns vary in size and flexibility, which enables us to select the thorn that is most appropriate for a particular object.

Thorns fresh from the garden waiting to be clipped

Figure 4. Thorns fresh from the garden waiting to be clipped.

Thorns clipped, sorted and ready for use in the studio

Figure 5. Thorns clipped, sorted and ready for use in the studio.

In addition to being softer than steel and safer to use on hoard objects, using thorns in conservation has other indirect benefits:

  • Thorns are a natural product that is completely biodegradable, so they can be disposed of along with regular rubbish
  • They are a sustainable and renewable product
  • They are free of charge and in abundant supply in the back gardens and allotments of Britain, so they do not affect our budget
  • Unlike cocktail sticks, they do not tend to split and splinter; instead, the point grows dull or the entire thorn snaps in half, at which point it is simply thrown away
  • They are safer; a conservator is far more likely to sustain an injury from a steel blade, pick or pin than a natural thorn, though we do always wear gloves while working to protect ourselves and the objects

A few potential risks to using thorns have been identified, the first one being that insects might hitch a ride into the studio on the thorns and their associated branches and leaves. To minimise this risk, bags of thorns are inspected prior to being brought into the museum, at which point they are held in the conservation offices instead of the studio until they are ready to be clipped. The second risk is that some natural substance such as plant juice/sap might be transferred from the thorns to the objects. To minimise this risk thorns are inspected and only dry, clean thorns are used. The thorns brought in have been quite dry and no leaching of any substance has been observed.

Use of natural products for conservation is nothing new. Porcupine quills and cactus spines have been used by conservators for some time, but as far as we are aware thorns are not being used elsewhere in conservation. If you know of conservators elsewhere using thorns for other projects please do let us know.

See a video blog  of our student interns, Evelyn Ayre and Arianna Carini, preparing thorns for use on the hoard.

Our thanks go out to the Friends of BMAG for their support and for so generously donating thorns for hoard conservation.

Cymbeline Storey

Staffordshire Hoard Conservator

Birmingham Museum & Art Gallery