A Chinese proverb says, “Gold cannot be pure and people cannot be perfect.” Fineness is perhaps the most important parameter when considering the quality of a gold item. Several different methods can be used to define this value, from the merely comparative touchstone method to the extreme precision of inductively coupled plasma mass spectrometry (ICP-MS). Among these, fire assay is certainly the most used. Although it is intuitive and reliable, this method has some drawbacks: It may be operator/environment sensitive, it can have limitations in the analysis of certain alloys and, most important, it is a destructive test. According to new market requirements, which demand a fineness test for every single piece, it is clear that a destructive method is no longer applicable. X-Ray Fluorescence (XRF) is a non-destructive test for compositional analysis of jewelry but it requires knowledge and judgment to avoid false values. The aim of this work is to review the underlying physics of the test method and define the correlation between sample characteristics (shape, roughness, dimension, composition) and analysis output in order to draw a reliable operational technique. 

Author: Dr. Marco Actis Grande