What XRF actually does
X-ray fluorescence spectrometry, XRF for short, is a method of measuring what elements a piece of metal is made of without damaging it. A handheld instrument fires a controlled, low-energy X-ray beam at the surface of the item. The atoms in the metal absorb the energy and re-emit it at characteristic wavelengths, each element has its own fingerprint, and a detector inside the instrument reads those wavelengths and reports the composition in seconds.
In practical terms, the operator places the item against the test window, holds the trigger, and a few seconds later a screen shows percentages: gold, silver, copper, zinc, palladium, nickel, and any trace contaminants. The piece is not scratched, filed, drilled, heated or chemically treated. It comes out of the assay in exactly the same condition it went in.
Why hallmarks alone are not enough
A hallmark is a maker's declaration of intended purity at the moment a piece was made. Real items have life histories. A wedding band made in 1965 may have had the inside re-sized in 1982 with a different alloy. A signet ring may have had its stone reset in 1991, with the new claws soldered using a lower-carat solder. A snapped chain may have had a replacement link added in 2003 from whatever the jeweller had on the bench. The hallmark on the original part is unchanged. The metal of the whole piece is no longer uniform.
XRF reads what is actually present today, including solder joints and replacement parts. Sometimes that is slightly below the hallmarked purity, occasionally slightly above. Either way, the charity is paid for what is in the parcel, not for what the maker claimed half a century ago. For a trustee or auditor reviewing a roll-up, that distinction is the difference between an asserted figure and a measured one.
What XRF can read confidently
- The percentage composition of solid gold, silver, platinum and palladium pieces, to a fraction of a percent
- The presence of trace elements like cadmium, nickel and zinc, which matter for refiner pricing
- The difference between a solid alloy and a plated piece, in seconds, on the same window
- Whether two parts of one piece (band and clasp; ring and setting) are the same alloy or different
- Whether an unmarked piece, suspected by the donor to be gold or silver, contains those metals at all
Each reading produces a numeric record that can be attached to the parcel reference on the written valuation. That is the audit-friendly outcome a trustee briefing values: not "we think it was 18ct" but "the XRF reading on day of valuation, attached to parcel reference, shows 74.8% gold".
What XRF cannot do
Important limitations a charity shop manager and a trustee should know.
- It does not value stones. Diamonds, sapphires, rubies, emeralds and pearls are valued separately by gemmological assessment, not by XRF. A diamond ring sent to GoldPaid is XRF-assayed for the metal, and any stones are appraised through specialist channels with the working shown in the written report.
- It does not read through thick plating without surface preparation. XRF reads the top few microns of metal. On a heavily-plated piece with a polished gold surface, the initial reading will look gold-rich. A trained operator spots the wrong composition profile, files a tiny test point on a hidden surface, and re-reads to confirm the core. This is the only situation in which any surface preparation may be needed, and it is done on a non-visible point.
- It does not value design, provenance or maker. A signed designer piece by a well-known UK maker, or a piece with significant antique value, is worth more than its metal content. Those pieces are routed to specialist valuation rather than scrap, with auction comparables cited in the written report.
- It does not measure weight. XRF tells you what is in the metal; the calibrated scale tells you how much there is. Both feed into the calculation.
How GoldPaid builds a defensible offer
- 1. XRF assay. Each item is read on the test window. The composition is logged against the parcel reference.
- 2. Calibrated weighing. Each item is weighed to 0.01 gram on calibrated scales. Mixed lots are separated by purity first, so 9ct is never paid at an 18ct rate.
- 3. LBMA benchmark price. The fine metal content is priced against the London Bullion Market Association PM fix on the day of valuation, the recognised global benchmark used across UK bullion and refining.
- 4. Written itemised offer. The charity's head-office contact receives a written report showing the XRF composition, the weight, the rate used, and the offer for each line item.
- 5. Payment or return. If the offer is accepted, payment is by Faster Payments to the charity's registered bank account, same day where the offer is accepted before 3pm UK time. If the offer is declined, every item is returned, free, tracked and insured. Free insured return of any item the charity chooses not to sell.
Why this matters for the trustee audit trail
A charity board has a duty to make decisions on evidence and to keep records that withstand independent scrutiny. The default disposal route for unsorted specialty donations, sale to a weighbridge scrap buyer, produces a single cheque with no per-item breakdown. There is nothing to audit against, and no way to detect under-payment after the fact.
An XRF-based valuation produces a per-item record. The trustee briefing pack on a monthly roll-up can show: which shops sent what, the composition of every item, the weight of every item, the benchmark rate used, and the offer arithmetic. A finance director can check any line item against the LBMA fix for the relevant day. A trustee with no specialist background can verify that no part of the process is hidden.
For multi-shop charities, that level of evidence is what allows a board to compare disposal routes properly. The trustee briefing sets out the seven questions a board should ask before approving any new supplier arrangement, and the XRF-plus-LBMA pricing model is structured to answer all of them on paper.
Common volunteer questions about the technology
Is X-ray safe?
The XRF instruments used for metal assay run at very low X-ray energies, fully shielded, and trained operators follow standard radiation-safety protocols. There is no residual radiation on the piece after the reading. A piece returned to a charity shop is no different from a piece that has been weighed on a kitchen scale.
Does the reading change the metal?
No. XRF is a non-destructive method. The X-rays cause the atoms to fluoresce momentarily; nothing is removed, added or chemically changed. The piece is unchanged by the test.
How accurate is it?
For solid gold and silver alloys at typical jewellery purities, modern XRF instruments read composition to within a fraction of a percent. The accuracy is comfortably enough for fair-value pricing and is the same technology used by mainstream UK bullion dealers and assay-office reference labs.
When XRF is most useful for a charity
XRF earns its place when the piece is uncertain. A clearly-hallmarked 18ct ring barely needs the technology; the hallmark is a strong indicator. The technology earns its keep on: pieces with missing or worn hallmarks, pieces with replacement parts and solder repairs, mixed lots of unknown small items, plated pieces that look very convincing, and any item where the donor history is unreliable. In all of those cases the XRF reading is the only way to give the charity an honest, evidence-based figure.
A shop manager who sends a parcel knowing the items will be XRF-tested is sending evidence into a measured process, not asking for a verbal guess. That changes the trustee conversation about charity-retail specialty disposal from "we hope we got a fair price" to "here is the per-item evidence". Indicative figures move with the market; the firm offer is set only after XRF assay confirms purity and weight of the specific items sent.
Common questions
Is XRF the same as an acid test?
No. An acid test files a notch in the piece and applies a chemical reagent to estimate the carat. XRF is non-destructive, reads the elemental composition directly, and is far more precise.
Will XRF tell us what a piece is worth on the open market?
XRF tells us the metal composition. Weight and the LBMA benchmark rate on the day of valuation translate that into a metal-content figure. Items with design or antique value are routed to specialist valuation rather than priced on metal alone.
Can XRF read the inside of a hollow chain?
It reads the top few microns of the surface. On hollow gold chains made of solid gold sheet, that reading is accurate for the alloy. On plated hollow pieces it reads the plating, which is why a trained operator checks for the wrong composition profile and prepares a discreet test point if needed.
Does XRF need the piece to be cleaned first?
No. Surface dirt and tarnish do not stop XRF from reading the underlying metal. A gentle wipe is fine; no abrasive polishing is needed.
How long does an XRF reading take?
Seconds per item. The bottleneck for a parcel of mixed pieces is sorting and weighing, not the assay itself.
Can we have the XRF reading on the report?
Yes. Each item on the written valuation shows the XRF composition, the weight, the rate used, and the line-item offer. That record is what a trustee or auditor can verify independently.
What about pieces that have stones?
The XRF assay reads the metal. Any stones are appraised separately, with the working cited in the written report. A diamond ring is never priced as scrap.