However, it only measures the
gold content of a thin surface layer,
so accuracy is severely compromised where the jewellery article has had a
chemical surface treatment (to enhance colour) or has been electroplated
with a layer of pure gold.
The more accurate XRF
instruments measure the intensity
of the generated gold X-rays by wavelength dispersion analysis. The use of
energy dispersive analysers results in cheaper instruments but reduced
accuracy. Reference alloy standards, of known
composition close to that of the test piece, are needed if accuracy is
required in XRF testing.
There are several instruments
appearing on the market developed specifically for gold jewellery assaying,
such as the X-tester, and these are more reasonably priced.
A major jewellery retailer in
has equipped each of their stores with such instruments. The gold content
of each piece is measured as it is sold, printing off a Certificate,
guaranteeing caratage conformance and providing consumer confidence in a
country where national Hallmarking regulations do not exist.