ED-XRF analysis techniques are becoming increasingly popular in the jewelry industry. The possibility of measuring a finished object of even complex shape, without destroying or ruining it, very quickly, is a unique attraction compared to other conventional techniques (e.g., ICP or fire assay). Despite their relative popularity, however, X-ray fluorescence-based techniques were generally relegated to a marginal role, limited to checking the rough composition, due to the perception that this type of measurement is inaccurate. Calibrating the analyzer with good references, choosing specific measurement parameters, and understanding the structure of the analyzed jewelry are fundamental in allowing much more precise and accurate measurements. In our tests, we work with and on the new ISO 23345:2021, which defines calibration, measurement, and interpretation of data for fineness analysis by ED-XRF.