East Kirk of St Nicholas dig June 2008
East Kirk of St Nicholas dig June 2008
Conservator Margot Wright, Senior Curator, Marischal Museum writes:
The small finds from St Nicholas are now in Marischal Museum conservation laboratory.
They comprise coins, both copper alloy and silver, many shards of window glass, some of which are decorated with maroon-coloured/ochre paint. The glass is very fragile and exhibits various forms of decay such as pitting, laminating, iridescence and just falling to pieces! Much of the glass is covered with a brown deposit that obscures any decoration and so each shard must be laboriously cleaned by swabbing with distilled water, taking care not to leave any of the cotton wool fibres on the surface, to expose any decoration. This is all carried out under a binocular microscope. The glass must then be consolidated to hold it together. Sometimes, when the glass is extremely vulnerable, it has to be consolidated before any cleaning is undertaken. If pieces are found to fit together then, where possible they are joined using a conservation-grade adhesive.
Fragments of bottles and bowls have also been found as well as spectacle lenses, pince nez and there is evidence that some of the glass has been in a fire as there are pieces of glass that have obviously been molten at some time and have solidified upon cooling.
The copper alloy is cleaned mechanically using a scalpel or pin vice under a microscope. Again, evidence must be preserved so that the coins may be identified and dated. Some of the coins have been cut into halves or quarters. After cleaning, the coins are immersed in a solution of benzotriazole (BTA) in ethanol and subjected to a vacuum to aid penetration of the solution. This is a particularly nasty chemical so the Control of Substances Hazardous to Health (COSHH) regulations must be closely adhered to. The artefacts are then rinsed in ethanol to remove excess BTA, the solvent is allowed to evaporate and then the coins are protected by applying two coats of a special lacquer. When the lacquer has dried, the coins may be safely handled.
Many shroud pins have been excavated. Consequently, because mechanical cleaning by scalpel and pin vice is very labour-intensive, a decision has been made to chemically remove the corrosion products to expose the original patina, after which, the pins are rinsed in distilled water to remove the chemicals and then they are treated in a similar manner to the coins. There are also many copper alloy shoe- and boot-lace tags.
Unusual finds include the denticle of a thornback ray that must have been caught in a pocket. The key to a fob watch, presumably the fob watch was found but couldn’t be wound.
There are some textiles that will be examined by a textile conservator to determine how they should be treated. Hopefully, the textile fibres will be identified, a weave count undertaken and perhaps even whether the fibres are ‘S’ or ‘Z’ spun.
Iron is a major problem, particularly when it is unstable. No treatments are entirely satisfactory. Generally, the iron artefacts are photographed, drawn and X-rayed.
They have to be stored at a relative humidity (RH) of less than 15% so that corrosion is inhibited or, at best, slowed down. Because of the nature of the site, many iron coffin fittings were excavated at St Nicholas’ and many still have the remains of the wooden coffins to which they were attached. The wood will be left in situ so that it may be identified. Because there is so much iron associated with the site, the archaeologists and conservator will examine the X-rays and decide which artefacts should be fully conserved.
Conservation is slow and painstaking but we are getting there slowly.
For further details, please contact judiths@aberdeencity.gov.uk
East Kirk of St Nicholas May 2008