In this case, we were requested to assist in understanding the origin of stains that appeared on the surface of 18K gold bracelets.

Examining the stains using Auger electron spectroscopy, it was found that the stains are the result of a 150 Angstrom deep surface layer composed mainly of silver and sulphur.

Specifically, a silver-rich sub-micron surface layer was detected and underneath this layer, a 24k gold sub-micron layer exists, the remaining material is compsed of 18K Gold. This surface structure is undesired, as the inertness of silver is inferior to that of gold.

The stains observed on the surface layer contain, in addition to silver, various contaminants originating from deficient cleanlinessof the coating baths. Therefore, in addition to eliminating the silver layers, an improvement of the process contaminant control was recomended.