How XRF Testing Works in a Hallmarking Laboratory

X-Ray Fluorescence (XRF) spectrometry is the primary analytical method used in BIS-authorized hallmarking centres for testing the purity of gold and silver articles.

The Science Behind XRF

XRF works on a fundamental principle of atomic physics. When a sample is irradiated with high-energy X-rays from the instrument's X-ray tube:

1. The X-rays displace inner-shell electrons in the atoms of the sample
2. Outer-shell electrons drop down to fill the vacancies, releasing energy
3. This released energy (fluorescent X-rays) has a wavelength characteristic of each element
4. A detector measures the energy and intensity of the fluorescent X-rays
5. Software calculates the elemental composition based on these measurements

Why XRF Is Ideal for Hallmarking

• Non-destructive — the article is returned to the jeweller intact
• Fast — results in seconds to minutes
• Accurate — modern XRF systems achieve accuracy within ±0.1% for major elements
• Comprehensive — identifies all elements present, not just gold or silver

Calibration and Quality

XRF instruments in BIS-authorized centres are calibrated using certified reference materials traceable to national and international standards. Regular calibration checks are mandatory to ensure ongoing accuracy.

Limitations

XRF measures surface composition, typically to a depth of 10–50 micrometres depending on the element and energy. For articles suspected of having surface coatings or plating, complementary methods such as fire assay may be used.