In my final months of my first year at Cardiff I worked as part of a project to clean and stabilise Anglo Saxon grave goods from Star Hill, near Bridge in Kent. The objects were part of an excavation that took place between 2005-2008. Unfortunately, they received no after care and much of the documentation was poor.
The main concern of the work was to clean and document the mineralised preserved organics (MPO) that covered much of the iron objects. This phenomenon occurs when the metal corrodes at a faster rate than the organics decay, and the form is recreated in the corrosion products.
I was allocated an iron knife, fragments of a second iron knife, a bundle of keys wrapped in MPOs and a number of small pieces of chatelaine. All these objects consisted of iron, some small elements of copper alloy and mineralised textiles. Aside from these I was also allocated six glass beads.
Most of the cleaning took place using hand tools under the microscope. A porcupine quill, stiff, short brush and glass bristle brush were used to remove the chalk matrix that remained. The chalk was present as both white clumps, and a more yellow composition that took on the shape on the textile it covered. Both were easily removed with careful abrasive action. Only the very soft chalk was removed as more abrasive action risked damaging the MPOs. This simple mechanical treatment was used for the chatelaine pieces, the bundle of keys and the broken knife. I really enjoyed this work, it required a steady hand and attention to detail, and am pleased with the final results.
The knife blade required treatment under the air abrasive unit to remove powdery corrosion products. Towards the handle end mineralised textiles were present, these were protected using cling film when in the air abrasive. I had had a little practice using the equipment and this helped me grow in confidence. The depth of the corrosion varied across the blade, which meant in some areas I quickly hit the metal below the magnetite layer. A bulging area that resembled weeping was left so as not to risk the stability of the blade.
Air abrading was also used to reveal the construction method of the chatelaine. Copper alloy wiring was utilised to connect short iron rods that created the chain. The best example of this wiring was identified using the X-ray images and chosen to be revealed. Using a little aluminium oxide powder to remove the iron corrosion that covered it, an echo of the original wire was revealed in iron magnetite. It is beautiful! I am very pleased with the results.
Finally, there was the cleaning and coating of the glass beads. This was carried out using IMS and ethanol applied using a cotton swab, and coated in Paraloid B72 5% in acetone applied with a small brush. The glass beads are lovely and the simple treatment was sufficient to bring out their detail.
I really enjoyed carrying out this work, much of which cannot be seen. The MPOs are fascinating and revealing the copper wiring was fantastic! It has sparked a growing interest in archaeological work just in time for my month in Çatalhöyük, Turkey, working with in-situ archaeological structures and newly excavated objects.