How Accurate is Portable XRF Compared to Fire Assay for Gold Analysis?

By: Publisher Team | Oct 29, 2020 20:32 PM
How Accurate is Portable XRF Compared to Fire Assay for Gold Analysis?

Pawn shops, jewellers, and cash-for-gold operations need to accurately assess if a piece of jewellery is made of real gold and precious metals or if it’s alloyed with other metals, and more importantly, the percentage of the precious metal content so value can be determined.

You cannot always tell the exact metal, or the percentage of precious metals in a piece, just by looking at it.

Fire assay is the most accurate technique, and is considered the legal method for gold hallmarking, but it is a destructive method because you have to melt the piece in order to determine the gold or other metal concentration.

Portable X-Ray Fluorescence (XRF) technology is another technique commonly used in pawn shops, cash-for-gold operations, and jewellery stores.  With XRF precious metals analysers, shop staff  can measure the content of all gold and precious metals, as well as determine the presence and concentration of other trace, alloying elements, and dangerous heavy elements, which could impact health and the valuation of the pieces. Most importantly, it is a non-destructive technology, so the piece does not lose any value during testing. This is an especially important factor if you’re dealing with high value items.

To alleviate concerns, we conducted a study, tested samples, and compared XRF precious metals analysis with fire assay. We analysed six large, flat items made of different types of gold with various grades and various compositions, and we found that accuracy was typically within 0.1 or 0.2% of the fire assay results.

We then analysed small, irregular samples and found out that the accuracy was better than 0.5 weight percent. Here’s a chart so you can see at a glance the results for the various pieces of gold.

There are a few exceptions to this study.  We do not recommend using portable XRF analysis on gold-filled jewellery, gold bars and bullions. If it is used, we strongly suggest that a secondary analysis is done just to ensure the absence of thick plating or any adulteration.

Source: Thermo Fisher Scientific – Analyzing Metals

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