Methods for the Testing of Tarnish

Abstract

The various regimes usedfor tarnish testing of metals are reviewed. They can be subdivided into gas-phase and liquid-phase tests. The effects of parameters suchas temperature, relative humidity, light intensity, on tarnish kinetics are discussed. Attempts to correlate laboratory withfield tarnish trials are considered. The chemical processes taking place during these tests are discussed. On the evidence, it would appear that conditions of pH, and local potential of the moisture films on the surfaces of the metals, change continuously during such tests. Depletion effects in the liquid phase tests do not suggest that these are reliable, the more so since the very species being tested catalyse depletion (air oxidation of sulphide ions).