Development of damage functions for copper, silver and enamels on copper

Abstract

This paper describes the development of damage functions for silver, copper and enamels using different representative environments in five historic buildings with a wide range of environments. The copper and silver corrosion rates were determined from Purafill Onguard 3 piezo-electric quartz crystals coated with copper and silver. The thermal deterioration of enamels has been of concern in conservation for some time. Such deterioration, occurring at the metal/glass interface, is difficult to assess visually. Acoustic emission is an extremely sensitive technique that can detect micro-cracking in rigid materials. Its use for enamels has been developed through a series of simple experiments. It was found that events are generated from the development of cracks, as small as 1 micron in length, at the metal/glass interface. A series of experiments in showcases with sensors attached to replica enamels with a conductive gel derived the damaging level of thermal shock, below which acoustic emission was not detected. Replacing the tungsten lighting with LEDs reduced the thermal load and no longer caused acoustic emission. Monitoring of historic enamel plaques (without the gel) replicated these results. Two correlation methods were used to remove environmental noise. Damage functions are normally developed from periodic measurements of a material’s deterioration and a multivariate fit to environmental data. There are questions about how to deal with semi-continuous data such as temperature and relative humidity for this process. Semi-continuous measurement is now available for some damage types such as the Onguard copper and silver piezo-electric quartz microbalances, resistance-based metal sensors and acoustic emission. The high sensitivity of these devices allows data to be collected at the same measurement interval as temperature and relative humidity logging (30 or 60 minutes). The development of damage functions provides an improved way to assess environmental data. It can allow a move towards more targeted standards, defining equal risk of deterioration, instead of the present prescriptive approach.

Cite this work

No public copy is stored for this record, so only the metadata is cited.

Stored only when both papers are in the corpus — 3 citations exist upstream.