How do you verify the karat when buying scrap gold?

Why is the karat of scrap gold verified separately?

Scrap gold is not a single batch: one bag can hold pieces of different karats, made in different workshops, some repaired, some plated. That is why the karat of each piece is verified separately, and no single karat is assumed for the whole bag.

Karat expresses the share of pure gold in the alloy out of 24; when the same ratio is written out of 1,000, it is called fineness. For example, 18 karat is 750 fineness; on 14 karat jewellery the karat stamp is usually 585.¹ The purpose of verification is to see whether the piece really contains gold in that ratio.

What does a stamp tell you, and what not?

A number such as 585 or 750 on the piece is often a karat stamp struck by the maker itself. Such a stamp does not show that an independent body has measured the piece; it is the maker’s declaration.² There are also marks that look like stamps but carry no karat meaning.²

If the stamp is accompanied by an abbreviation such as GF or RGP, or a fraction such as 1/20, the number describes the gold layer on the surface, not the whole piece. We explain these marks in detail in our article How can you tell plated gold? In short, the stamp is read and noted, but it is not accepted on its own as proof of karat.

What to watch for in a scrap piece

Situation	Why it matters	What to do
Mixed scrap	The pieces may be of different karats	Each piece is measured and noted separately
Soldered chain, earring, ring	Jewellery solders contain silver, copper and zinc alongside gold³	The measurement is taken at a spot away from solder points⁴
Suspected plating or filling	The surface layer may not be the same metal as the body	The piece is measured at several points; a destructive test is recommended if needed⁵
Dirty or worn surface	As plating wears, the metal underneath becomes visible	The surface is cleaned, and worn spots are checked separately

Solder is a separate alloy that joins the parts of a piece of jewellery. The hard solders used in jewellery contain a high proportion of the metal being soldered; gold solders are made of gold, silver, copper and zinc.³ So the composition at a solder point can differ from the body. GIA’s touchstone guideline also says to take the sample from a part of the piece that is not visible and away from solder points.⁴

Step by step at the jeweller’s bench

1SeparateSeparate the pieces in the scrap one by one; assess each one separately.

2Read the stampNote the karat number and whether there is an abbreviation such as GF or RGP, or a fraction, next to it.

3Choose a spotChoose a clean surface away from solder points for the measurement.

4MeasurePut the piece on the measuring window in the chamber. Close the lid and tap START.

5If doubt remainsIf you suspect thick plating or a filled piece, measure it at several points; a destructive test may be needed.

When buying scrap, measure the karat in front of the customer. The result appears on screen; the stamp, the visual check and the measurement are assessed together.

Measurement methods and their limits

Touchstone and acid: The piece is rubbed on a black stone; its streak is placed next to the streaks of needles of known karat, and acid is applied over them. By seeing which streak dissolves, the karat of the piece is found by comparison.⁴ The guideline also describes making a small notch in a hidden spot on the piece and dropping acid on the fresh metal: a strong, foaming green reaction shows that the piece is a metal that is not gold.⁴

XRF: The tube sends X-rays into the piece from below. Each element answers at its own energy: gold at 9.71 keV, silver at 22.16 keV. The detector counts these rays and the software turns them into ratios.⁶ The measurement involves no cutting, scraping or acid; the piece stays as it was before the measurement. XRF measures the surface: with thin plating, the base metal underneath (e.g. copper, zinc) shows up in the result and the plating is revealed.⁵

Destructive test: Fire assay is a method in which the sample is melted at high temperature and completely consumed; it is the accepted standard method for evaluating gold ore.⁷ If suspected thick plating or filling cannot be resolved by measurement, such a destructive test is recommended.

FAQ

Is a scrap piece stamped 585 definitely 14 karat?

No, not definitely. The 585 stamp is often the maker’s declaration; to verify the karat, the piece is measured.

Where should a soldered piece be measured?

At a spot away from solder points. The composition of solder can differ from the body.

Is one measurement enough for a bag of scrap?

No. Because the pieces may be of different karats, each piece is measured and noted separately.

Does XRF measurement damage a scrap piece?

No. The measurement involves no cutting, scraping or acid; the piece stays as it was before the measurement.

Can a thickly plated piece be detected with XRF?

XRF measures the surface. If you suspect thick plating or a filled piece, measure it at several points; a destructive test may be needed.

All values are measured under the manufacturer’s test conditions and may vary with the shape and surface of the sample.

Karat isn’t guessed. It’s measured.

Try the live analysis to see how a measurement looks on screen, or request a quote for your business.

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