The customer puts a thirty-gram bracelet on the counter, its 750 hallmark clearly legible. The buyer has a few minutes to price it while the customer waits, and the price hangs almost entirely on a number nobody can see: how many parts of gold per thousand the metal really contains. If the bracelet is a gold shell around a low-grade core, the hallmark misleads and the scale won't notice. This is what makes fineness testing the technical step that sets the margin of a gold buyer, a bullion dealer or a refiner. The XRF spectrometer made it fast and non-destructive. The number on the screen, though, only holds up inside a procedure. That procedure fixes what you look at before measuring, where you measure, when you file, when the piece leaves the counter for assay and what goes into the transaction record.
The number you are checking: parts per thousand, karats and the hallmark
The counter thinks in parts per thousand. A 750 is 18 karat, 750 parts of gold per thousand; 585 is 14 karat, 375 is 9 karat and 916 is 22 karat, while investment gold is expressed as 999 or 999.9. The hallmark promises a minimum, because article 3 of Italy's Legislative Decree 251/1999 rules out negative tolerances on legal finenesses, apart from a few exceptions. The full picture, with the legal finenesses of every precious metal, the official assay methods and the ISO standards, is in the article on method and standards for XRF analysis of gold and precious metals.
For a buyer the consequence is practical. A 750 that reads 740 at several clean points deserves a second look, provided the gap exceeds the uncertainty the instrument has demonstrated on that alloy type. If you don't know your instrument's uncertainty, you have no way to read any gap at all.
What to look at on the screen besides the fineness
Within seconds, or a few tens of seconds when more precision is needed, the spectrometer returns the fineness and the spectrum, and the two belong together. The fineness tells you how much gold sits in the measured spot; the spectrum tells you what it is alloyed with. Unexpected nickel in a yellow gold, rhodium on a white gold or silver too high for the color of the piece are clues the number alone would hide. Precision improves with measuring time, because statistical uncertainty falls as counts accumulate. Marco Actis Grande's paper at the 2016 Santa Fe Symposium makes exactly this point. The shape, roughness, size and composition of the piece shift the result, and only a sound operating method keeps false values out.
Then there is the limit that shapes the whole procedure. The gold signal comes from a few micrometers below the surface, about 4 in pure gold according to NIST attenuation coefficients, so the instrument reads the skin of the piece. The physics of that limit, line by line, is explained in the analysis of XRF measuring depth in gold. On a homogeneous piece the skin represents the core, and the rest of the procedure exists to tell when it doesn't.
Touchstone, hydrostatic balance and XRF: what each one sees
The touchstone survives because it is cheap and works anywhere. You streak the piece on the stone, apply acids matched to different finenesses and watch whether the streak holds. The result is a band, along the lines of "at least 585", and it depends on the eye of whoever runs the test. The stone shares XRF's main limit, since it too reads only the surface. A portable XRF analyzer, or a bench unit, adds a numerical value, the full composition and a spectrum you can store, show the customer or attach to the transaction record.
A hydrostatic balance measures density by weighing the piece in air and in water. It's a good check on bars and compact shapes, and a much weaker one on jewelry with stones, cavities or solder joints. The benchmark for all of them remains the cupellation of ISO 11426:2021. Christopher Corti, in his review of gold assaying at the 2001 Santa Fe Symposium, calls it the technique against which all others are compared. It destroys the sample, though, and needs a laboratory. Nobody cupels the wedding ring a customer brings to the counter.
The verification sequence for an item at the counter
A procedure that stands up to a dispute is short and runs the same way for every piece. Written down, it also becomes the tool for training whoever works the counter:
- intake: weight, photographs, reading the hallmark and identification mark under a loupe, looking for spots where wear shows a different color;
- cleaning the measuring spot of grease, dirt and polishing residue;
- readings at no fewer than three points, one of them in a worn or hidden area such as the inside of the clasp or the shank of a ring, away from solder joints and settings;
- comparing fineness, spectrum and hallmark, watching for elements that shouldn't be there;
- if readings disagree or the gap exceeds the written threshold, filing a spot that won't show, with the customer's consent, and measuring again;
- if doubt remains or the piece is valuable, a density check and assay;
- recording the reading and the spectrum with the transaction record.
Gold-plated items: the opening bracelet, measured
Thin electroplated gilding still lets the signal from the underlying metal through, and a spectrum showing silver, copper or zinc in proportions that don't fit the reading is already a warning. As the layer grows towards a few micrometers, the core signal fades and the instrument sees only the gold skin. Even with no intent to deceive, pickling and finishing can leave the surface richer in gold than the core, so readings come out above the true fineness.
Take a worked example built on the opening bracelet, assuming a homogeneous alloy under the gilding. Three ten-second readings on the links come out between 748 and 752, in line with the hallmark. A fourth reading inside the clasp, where wear has rubbed the surface away, gives 590 with copper and zinc clearly visible. Filing a hidden spot confirms the second value. This time the hallmark was lying. From that point the bracelet has to be treated as gilded 585. On thirty grams, the gap between the two finenesses is worth about five grams of fine gold (30 × 0.165), paid for and never received.
The step that saved the purchase is the third one, the reading in a worn area, and it is the first one at risk of being skipped when the counter is busy. Some instruments also offer a coating-thickness mode, useful when you already know the piece is gilded and need to know by how much.
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Email us Message us on WhatsAppSmall bars and tungsten cores: when you have to look inside
With bars the risk changes shape. Tungsten's density is almost identical to gold's, about 19.3 grams per cubic centimeter for both, so a gold-clad tungsten core can pass a routine hydrostatic weighing as well as XRF, which sees only the shell. It is the worst case for a buyer. The LBMA, looking back at the concerns raised in the early 2000s, reports that such inserts were found in small bars but never in the large bars of the Good Delivery system. The same page notes that most London vaults installed ultrasonic testing equipment in those years.
Ultrasound works because sound travels through the two metals at very different speeds. René Böttcher and Lothar Spieß of Technische Universität Ilmenau presented the case in a poster at the 2014 annual conference of DGZfP, the German society for non-destructive testing. For longitudinal waves they report 3,240 m/s in gold and 5,261 m/s in tungsten. Sound in tungsten is therefore about 1.6 times faster, and the back-wall echo of a bar with an insert returns sooner than its thickness would predict. The same authors note that the fakes are clad in a gold layer thick enough that X-ray fluorescence does not get through it. For a bullion dealer buying small bars from private sellers, the practical rule is to pair the surface reading with a check that goes through the piece, accurate density or ultrasound, before paying full value.
Who sets the acceptance threshold at the counter
The law sets the finenesses and the official methods of analysis, and fineness inspections fall to the Chambers of Commerce, which take samples and have them assayed by authorized laboratories. No rule says when a gold buyer may trust an XRF reading. That threshold is set by the operator. It is worth writing down, spelling out which deviation from the declared fineness triggers a second reading, which one triggers filing, which one sends the piece to the assay lab.
The basis for setting it is the uncertainty the instrument demonstrates on samples of known fineness from the same alloy family, re-checked at regular intervals. Without that rule, a three-digit number is just an opinion.
The transaction record and where measurement helps
Since 2017 the trade has been governed by Italy's Legislative Decree 92/2017. Articles 3 to 6 require registration with the OAM register, customer identification and traceable payments from 500 euros upwards. Every transaction then needs a numbered record with a description of the item, the metal price taken from a reliable and independent source, the valuation and two digital photographs from different angles. The record has to be kept for ten years. The decree doesn't require a measuring instrument. An XRF reading saved with its spectrum, however, makes the valuation in that record reasoned and traceable, and protects the dealer when a customer or an inspector challenges it. Since 17 January 2025, as the Bank of Italy notes, professional gold operators under Law 7/2000 also fall under the OAM, following Decree 211/2024.
There is one boundary every buyer should know. The counter spectrometer produces a technical and commercial assessment, while official assaying of fineness and hallmarking belong to laboratories and enforcement bodies. Promising a customer a certification the instrument cannot issue is a professional mistake.
Training and routine checks: who measures, and by what method
A written procedure is only as good as the people applying it. Whoever works the counter has to read a spectrum as well as a number and spot rhodium or nickel out of place. They also need to know where to measure on a chain and where to avoid it on a ring with stones, and know the thresholds that trigger filing or assay. Training pays off most on real pieces, ideally a small in-house collection of items of known fineness that includes at least one plated piece and one rhodium-plated white gold.
Each working day can start with a reading on a reference sample, logged in a register. If the reading drifts beyond the set gap, the instrument gets re-checked before the first piece is valued. Two minutes make every reading of the day defensible. A portable or bench X-ray spectrometer also brings the radiation-protection duties of Italian Legislative Decree 101/2020, which differ between a shielded unit and a handheld one. The offer should make clear who takes care of them.
When a counter reading closes the deal, and when the lot goes to assay
The line runs through the value at stake. For used jewelry gold that is homogeneous, clearly hallmarked and consistent across several readings, a methodical XRF measurement is enough to close the deal. Items with conflicting readings, small bars from private sellers and lots heading to refining are a different matter, because a few parts per thousand weigh on kilograms of metal. There the surface reading becomes the filter that decides what goes to assay. A counter with few purchases, almost all standard hallmarked jewelry, can stay with a touchstone and an outside lab. An instrument starts paying for itself as volumes, doubtful items and disputes grow, and the numbers can be worked out with the method in the guide on what a handheld XRF analyzer costs and returns.
One criterion holds the rest together: the higher the value of a single piece, the more the decision moves from the counter to the lab. To choose between configurations, from detector and precious-metal calibrations to format, the guide to choosing a portable XRF analyzer helps. So do the page on XRF and PMI spectrometers for material analysis and the one on the portable XRF analyzers we distribute. If the decision concerns your own counter, the next step is a test on your typical items, before any proposal.
What to send us for an assessment
To set up a test that is useful for your counter, we need a few details:
- types of items you buy (mixed scrap gold, wedding bands, chains, coins, small bars) and their share of the total;
- metals you handle besides gold, such as silver, platinum and palladium;
- number of purchases per day or per week and peak periods;
- current testing method (touchstone, hydrostatic balance, outside lab) and disputed cases in recent months;
- preference between a shielded bench instrument and a handheld one, with the space available;
- how you record the valuation in the transaction record today and whether you want to archive spectra.
You can send them by email to info@dipitech.com or on WhatsApp, with a few photos of your most common items.
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Frequently asked questions on verifying gold fineness at the counter
How do you verify gold fineness without damaging the item?
With X-ray fluorescence: the instrument reads the surface composition in seconds, without acids and without removing metal, and returns the fineness in parts per thousand together with the spectrum. On doubtful items it should be backed by readings at several points and, where needed, a small file mark in a hidden spot or a density check.
Touchstone or XRF: which is more reliable at the counter?
XRF, because it gives a numerical value, the full composition and a spectrum you can archive, while the touchstone gives a fineness band that depends on the operator's eye. Both read only the surface, so neither one, on its own, exposes thick plating.
How do you spot gold-plated items with XRF?
By measuring at several points, including worn or hidden areas, and by reading the spectrum. Thin gilding still shows the metal underneath, while thick plating is exposed by a small file mark and a new reading. Bars and high-value items also need a check that goes through the piece, such as accurate density or ultrasound.
How do you detect a small bar with a tungsten core?
With a check that goes through the piece, because XRF reads only the shell and tungsten has almost the same density as gold. Ultrasound gives it away: sound travels about 1.6 times faster in tungsten than in gold, 5,261 versus 3,240 m/s in measurements by Technische Universität Ilmenau.
When should a piece be sent to assay?
When the gap from the declared fineness exceeds the threshold written in your procedure, or when readings at different points disagree. As a precaution it is also worth sending small bars bought from private sellers and lots heading to refining, where a few parts per thousand weigh on kilograms of metal.
How much does an XRF spectrometer for gold buying cost?
It depends mainly on two things: the format, bench unit with a shielded chamber or handheld, and how much of the procedure you want built into the instrument. That ranges from a spectrum archive linked to transaction records to gilding-thickness measurement. DIPITECH prepares a tailored quote within 24 hours and arranges a test on your own items, so the choice starts from real readings.