How to test gold at home: which checks mean something, and which will damage it

01

What a home test can settle, and what it cannot

A kitchen test has one job. It sorts a drawer into the things that are probably not gold and the things that might be, so that you stop spending attention on the first group and start asking proper questions about the second. That is worth doing, it costs nothing, and it is the whole of what a home test achieves.

What it cannot do is give you a carat. The hallmarking guidance published by the Assay Offices of Great Britain states that it is not possible to detect by sight or by touch the platinum, gold, palladium or silver content of an item. That is why hallmarking exists at all. A piece can pass every check below and still be 9ct, 18ct, gold-filled or heavily plated brass, and those four are very different things.

02

The four checks worth running

None of these needs anything you would have to buy, apart from a cheap magnifier if you have none, and none of them puts a chemical on the piece.

1. A magnetAny fridge magnet will do, though a stronger one is better. Hold it against the body of the piece rather than the fastening. Gold, silver, platinum and palladium alloys are not attracted to a magnet. If a whole bangle, a whole ring or the length of a chain lifts towards it, that piece is not precious metal and you are finished with it. If nothing happens, you have learned that it is not steel, and nothing else.
2. Wear points and colour break-throughLook at the tips of chain links, the underside of a clasp, the edge of a ring shank, the high points of any raised decoration and the back of a pendant where it has rubbed on clothing. Coatings go from those places first. A yellow-pink or grey colour showing through means a different metal underneath, and one glimpse of it settles the question. Seeing no break-through means only that the piece is not worn through yet.
3. The marks, read under magnificationRest the piece on something plain and pale, bring the light in from the side rather than straight on, and look with the strongest magnifier you have. A phone camera at its closest focus works. You are looking for a number, for a small walking lion on silver, and for a shaped shield with initials in it. Marks are often worn, half-struck or filled with polish, and a mark you cannot read is not the same thing as no mark.
4. Weight against sizePick two pieces up, one in each hand, and compare. Solid carat gold is startlingly dense, and people who have never held any are surprised by it. A chain that feels lighter than it looks is hollow, plated or both. This is a comparison and not a measurement, and it works far better between two objects of similar size than on one object alone.

What each result actually licences you to conclude

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Read that table across rather than down. Three of the four checks tell you far more when they fail than when they pass, which is true of nearly all cheap testing. The sorting guide takes the same checks through a whole box rather than a single piece.

03

Why a magnet passing proves nothing

The magnet is the most useful thing in the drawer and the most over-read. What it finds is iron, in practice steel, and it finds it very reliably. The Royal Mint explains the same effect in circulating coinage: the 5p and 10p changed from cupro-nickel to nickel-plated steel in 2011, and it is the iron in the steel core that makes them stick.

That is the limit of the information. Brass does not stick. Bronze does not stick. Pewter, aluminium, zinc alloys and most costume-jewellery castings do not stick. Neither does gold. A piece that sits quietly against a magnet has told you it is not made of steel, and a great many worthless things are not made of steel.

The same goes for watch cases with a steel back on a gold front, spectacle frames with steel hinges, brooches with a steel pin and cufflinks with a steel swivel. Each of those is a mixed-material object where one small part is steel because steel is the right material for a spring. What the magnet is good for is the whole-piece pull, and a whole-piece pull is conclusive.

04

Reading the marks, in British notation

A British hallmark is several small marks struck together, and the one people mean when they talk about carat is the fineness mark. It is a number in parts per thousand, not a letter and a k. The approved standards for gold under Schedule 2 of the Hallmarking Act 1973 are 375, 585, 750, 916.6, 990 and 999 parts per thousand. On jewellery, the first four are the ones you will meet.

British fineness marks for gold and what each one is

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A piece marked 10k or 14k was made for a market that uses that notation, most often the United States, and those pieces reach British drawers constantly through inheritance and travel. They are not British hallmarks and the number is a manufacturer's claim rather than an assay office's finding. The hallmarks guide sets out what a full British mark contains and which foreign marks mean what.

A missing mark is what people most often misread. Articles below a certain weight are exempt from compulsory hallmarking, and for gold that weight is one gram, so a stud earring, a fine chain or a thin band may carry nothing and be perfectly good. The Assay Offices' guidance adds that any pre-1950 item may be described and sold as precious metal without a hallmark if the seller can prove it meets the minimum fineness and was made before 1950. A heavy unmarked piece, on the other hand, has not been identified yet, and only a test settles it.

05

The folk tests, taken one at a time

Search for this subject and you will be shown the toothpaste, vinegar, lemon, ice, lighter, ceramic streak and float tests, usually as a numbered list with no verdict attached. Here is the verdict, method by method, with what each one actually measures.

Seven household methods and what each is really measuring

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Two of those deserve more than a line in a table. The lighter test does real harm, because heat does not stop at the surface. It softens the metal, takes the temper out of a spring and opens the solder at a link or a setting. It will craze or burn pearls, amber, coral, opal, turquoise and emerald without warning. A piece worth keeping as jewellery can stop being worth keeping in ten seconds.

The acid test is the other. It is a long-established trade method, not a home one. The Goldsmiths' Company Assay Office describes touchstone testing as lightly rubbing the article onto a stone of basanite. Every other traditional method it lists needs a physical sample taken from the article by scraping or drawing. Testing acids are corrosive, and applied to the piece rather than to a streak they leave a permanent dull mark. No procedure for either is given here, and it is wise to be wary of any page that gives one.

06

Carat is the number, and no kitchen test reaches it

Suppose every check goes your way. The magnet ignores the piece, the wear points are clean, there is a mark you cannot quite read, and it feels heavy for its size. You now know you are holding something that might be gold. You do not know whether it is 9ct or 22ct, and 22ct holds well over twice as much gold as 9ct in the same weight of metal.

That is why the home tests stop where they do. Establishing a fineness needs an instrument or a laboratory, and more than one method, because each has a gap. The Goldsmiths' Company Assay Office uses non-destructive X-ray fluorescence alongside touchstone work, cupellation, titration and, for platinum and palladium, ICP analysis. It notes that on occasion the surface layer has to be removed to find out what the alloy underneath is. The XRF guide explains where surface reading goes wrong, and the testing page sets out the methods Assaypost uses.

The most useful thing you can do at home is not a better test but a better photograph. A sharp picture of a mark, a worn link tip and the whole piece beside a ruler answers more than any of the seven methods above. It lets a person who reads hallmarks tell you what you are holding before you post anything. That is what the photo route is for, and the sell gold page explains what happens after it.

07

Seller risks and exceptions

• Testing a piece that should not be tested. A signed brooch, a pocket watch or a piece of antique silver can be worth considerably more intact than as metal, and a scratch, a burn or an acid mark on it is money gone. Identify first, test later, and see what to keep back.
• Reading a pass as a result. Three of the four checks only tell you something when they fail. A piece that passes all four has not been identified; it has only survived elimination.
• Trusting a number stamped on a piece. A fineness mark on an unhallmarked item is a claim by whoever struck it. Gold-filled stock is stamped with a real carat and a fraction, and thickly gilded pieces are stamped with plating codes that look like fineness marks.
• Cleaning or polishing before you photograph. Polishing takes metal off the highest points of a piece, which is exactly where the hallmark is. See whether to clean before you sell.
• Assuming a magnet-free clasp means a gold chain. Plated brass does not stick to a magnet either, which is why the wear points and the weight matter alongside it.
• Forcing a watch case back to look for marks. Cases are fitted, snapped or screwed, and a slipped knife marks the case and the movement. A jeweller opens one in seconds.

08

When not to test it yourself at all

For those pieces the sensible first move costs nothing and changes nothing. Photograph the marks and the piece and ask what it appears to be, or take it to a valuer or a saleroom and ask for an opinion. The guide to valuation, appraisal or offer sets out which of those you actually need and which you do not, and what we buy says plainly which materials are taken here and which are not.