Ten ways to test gold, silver and platinum
HOW TO CHECK GOLD AND OTHER PRECIOUS METALS
CONTENTS
VISUAL TESTS
MAGNETIC TESTS
HARDNESS / MALLEABILITY
THE ACID TEST
TEN COMMON QUESTIONS ABOUT THE ACID TEST
DE-PLATING
XRF (X-ray Fluorescence)
SPECIFIC GRAVITY (RELATIVE DENSITY)
RESISTIVITY
ULTRASOUND
MELT-AND-ASSAY (FIRE ASSAY)
ICP
RELATED ARTICLES
VISUAL TESTS
Before you start, LOOK at the item. And if you can’t see clearly (and nobody can see see tiny hallmarks with the naked eye!) buy a good quality jewellers loupe, it will be the best ‘tester’ you ever own. All modern gold, silver and platinum items made in (or imported into) the U.K. should be hallmarked.
Hallmark charts illustrating hallmarks must (by law) be displayed wherever precious metals are bought or sold. Familiarize yourself with these marks.
Alongside the hallmark is also a date letter, and you can look up the date letter in a hallmark book, there's one for British hallmarks and one for international hallmarks. This is useful for dating antique items.
There are dozens more 'general knowledge' hints and tips in The Gold & Silver Buyer's Handbook, £12.50 postage-free.
MAGNETIC TESTS
Gold and silver are not magnetic. So if it's magnetic it can't be gold or silver. But NOT being magnetic doesn't prove anything, copper (which is often plated with gold) is not magnetic, some steel is not magnetic. Also, a magnet won't help test white metals, some steel is not magnetic, some platinum is magnetic.
Some metals (e.g. copper and silver) are diamagnetic. Slide a tiny magnet down a flat item (or a coin) and it will set up a "field" that will slow it down. We sell special sets of magnets for this purpose. There is also an article specifically about testing gold, silver and platinum with magnets.
HARDNESS / MALLEABILITY
Precious metals are soft, large thin gold items (especially if made of high-carat gold) bend easily in and out of shape. Also, before testing the item you will have to file the surface with a fine steel file (otherwise you will merely test the surface plating). This is a good test in itself, you will soon see how easy it is to file gold or silver whereas the steel file will 'bounce off' an item made steel - no need to test any further.
THE ACID TEST
You've tried all of the above, you may have your suspicions, but now you need absolute proof: the acid test.
The two most popular brands of tester are QUICKTEST and TROYTEST. They comprise small bottles of acid in a wooden box. All sets test for gold (all carats) and silver; advanced sets also test for platinum, palladium and steel. There is a short article listing what each set (and each bottle) tests, for, click here to read it. Or to skip all articles and go straight to the products where you have the option to buy, click here (there is detailed information with each product description).
This is what you do
Choose a place on the item that is not normally seen and file the surface (a fine needle file is included with each set). Do this firmly but only over a very small area. This is to get past any plating, because if the item is gold plated, the surface IS gold and will test as such. Now put a tiny spot of acid on the filed area of the item. The acid will change colour, and that tells you whether the item is gold (and also the carat) or silver.
For gold, acids are designed to test to the nearest carat commonly used in jewellery, 9ct, 14ct 18ct, 22ct – but, with practice, results to within 5% can be achieved, very accurate! On silver, the acid gives a very definite reaction on Sterling (.925) silver, a slight reaction on 'low-grade' (.800) silver, and hardly any reaction at all on very low grade (.500) silver.
TEN COMMON QUESTIONS ABOUT THE ACID TEST
Q. How reliable is the acid test?
A. Very reliable. It has even entered the English language, we say (referring to ultimate proof), "The acid test is…"
Q. Will the acid test 'test' through gold/silver plating?
A. No, you must file the item first (a very fine needle-file is included with each testing set) so that you are testing whatever might be underneath any plating. You must file the item before carrying out a test with any electronic tester (unless the plating is very thin).
Q. Do I put the acid on the filings that have been taken off with the needle file?
A. No, you put the acid on the actual item
Q. Do acids cause any damage?
A. You must file it in a place where it won't show. If you can't file it you can't test it. On 9ct (and sometimes 14ct) the acid it leaves a stain. This can be polished off with a soft cloth.
Q. Are acids easy to use?
A. You need to spend a few minutes practicing, but the instructions are very clear, it really is not difficult.
Q. Do I need to wear special protective clothing when using acids?
A. As with all chemicals (e.g. household cleaners) you may wish to wear an apron to protect clothes. Small drops of acid stain small spots of skin yellow (if you’re careful, you shouldn't spill any!) and it can take a few days for the skin to grow back. I recommend that you buy special acid-proof disposable gloves (they come in boxes of 100 and are not expensive).
Q. I am colour-blind, how will I see the colour-change of the acid?
A. Unlike other brands you don't have to distinguish between reds, greens and browns. There are special instructions explaining what the "colour change" looks like to anyone who is red-green colour blind.
Q. Can acids test for white metals including testing platinum?
A. Yes, the Troytest (4-bottle set) and Troytest-5 (5-bottle set) can distinguish white gold, platinum, steel and Palladium.
There is a huge amount of information in The Gold & Silver Buyer's Handbook, £12.50 postage-free.
DE-PLATING
This is the most common type of 'low-cost' (under £500.00) tester.
How they work: a microscopic amount of the metal is 'dissolved' into an acid or salt solution - but it's only the non-gold that will dissolve, so the machine calculates the percentage of metal that has not dissolved = the percentage (in 'carat') of gold. Ease-of-use: easy (we have experience in using several models). Limitations: not reliable on platinum, can't test silver. Will not 'read' through plating, you must file the item so that you are testing whatever might be underneath any plating. Safety: the salt-solution versions are safe. Cost of tester: the cheapest use a strong acid to dissolve the sample (about £100.00), the good models use a harmless salt solution (about £350.00). Cost of consumables: the 'pen-probe' with the salt solution lasts a few hundred tests, replacements are about £50.00. Availability: we sell the best model, the KEE tester.
Some people complain about the cost of the KEE and replacement probes and want to know about "better" testers that "aren't so expensive to run". The answer:
1) Sets of acids (see above) are cheap, replacement bottles are cheap, no batteries, they don’t go wrong, they are more accurate than de-plating testers, and they test for white metals including silver, platinum, Palladium and steel.
2) XRF (see below) uses x-rays instead of a probe. However, unlike a KEE, you can't calibrate it yourself, if you are getting strange readings you must send it back the supplier who will charge a few hundred pounds for a ‘service and calibration’. When the ‘sensing tube’ wears out (or if you break it) a replacement costs over £1000.00. This puts the cost of running a KEE in perspective!
XRF (X-ray Fluorescence)
How they work: they fire x-rays a fraction of a millimetre into the item and see if it 'glows' (fluorescences). Ease-of-use: reasonably easy to use. I spent a few hours playing with one: impressive! Within a few seconds the display shows an approximate chemical composition of the metal; you need to wait a minute or two for an accurate reading. Limitations: Some models give you a 'probability' that the item might be plated but, to be certain, you need to file the surface so that you are testing whatever might be below any plating. Safety: They work on ex-rays, I see market traders holding each sample in their fingers whilst testing, they will get cancer. However, these testers are quite safe if used properly. Cost of tester: prices have come down immensely, the handheld versions are now about £10,000.00 and the 'cabinet' versions about £20.000. Cost of consumables: no 'consumables' but there are a few parts that cost £1000.00 each to replace when they wear out. They also need regular servicing which costs a few hundred pounds. Availability: we do not sell these, good makes are Niton and Fischer.
SPECIFIC GRAVITY (RELATIVE DENSITY)
How they work: weigh the item, weigh it again while it's immersed in water, get out your calculator and make a calculation. Ease-of-use: not easy, you really do have to work slowly and meticulously. Limitations: the cheaper testers can only hold small items; good for high-carat gold but not so accurate for low-carat gold. Safety: safe. Cost of tester: about £100.00 for an attachment for your own scale; a dedicated computerised balance, £1000.00 to £1500.00 (on special clearance from Quicktest) or £2000.00 to £3000.00 from other suppliers. Cost of consumables: none, just water plus, maybe, batteries for your balance. Availability: we have two models.
There is also a Sovereign tester, which works on the same principle, but simpler (no water required). A special 'tester' measures the diameter and thickness of the Sovereign; a weighing scale is included to weight it; if the size and weight are correct, then it's made of 22ct gold. There is also and antique version.
RESISTIVITY
How they work: measures the electrical resistance through a metal. Ease-of-use: complicated. The tester measures the resistivity in different directions and the size and will compare the readings with known values in the database (this is not something you can do with an electrical meter!) Limitations: limited to coins and small bars. You must know what the coin/bar is meant to be made of (e.g. 22ct) then the tester will indicate how close (e.g. to 22ct) the sample is. Safety: safe. Cost: about £2000.00. Availability: we don't currently sell these.
ULTRASOUND
How they work: they pass sound-waves through the object to see if it is the same all the way through or if it is 'filled' with another substance, e.g. a gold bar filled with non gold. Ease-of-use: complicated! You must measure the depth of the sample very accurately and you must use specialist software to translate the reading into something meaningful as regards gold. Limitations: measuring the sample is easy with flat bars, difficult with coins, impossible with jewellery. It will not detect gold plating; it will not tell you if the sample is made of gold, it will merely show that it's the same metal all the way through. Safety: safe (the same 'sound waves' as used in ante-natal testing). Cost: £750.00 to £1000.00. Availability: we don't sell these but it's a standard engineering instrument, e.g. to 'see' the inside of steel or concrete structures.
MELT-AND-ASSAY (FIRE ASSAY)
How it works: take a sample and weigh it. Then melt it and refine it, to leave pure gold. Weigh it again and calculate the percentage (in carat) of the gold. Ease-of-use this is not a 'tester', this is the method used in the laboratories of smelters. Limitations: it's destructive. Safety: smelting / refining is very specialist and skilled. Cost: we can send your gold for melt-and-assay, £95.00 + VAT (allow 2 to 3 three weeks). We are not bullion dealers, we do not buy gold, our charge is just for the service, we give you the result and send the gold back to you.
ICP
Inductively-coupled plasma mass spectrometry.
How it works: a tiny tiny amount of the gold is vaporised and the resulting light analysed. It uses a high-vacuum system, high energy electron beam and an X-ray detector. Ease-of-use this is not a 'tester', this is the method used in research laboratories and some Assay Offices. Limitations: it's destructive. Cost: from £50,000.00.
To see all precious metal testers, click here.
See also, The Gold & Silver Buyer's Handbook, £12.50 postage-free.
RELATED ARTICLES
More methods of testing gold (and other precious metals)
Acid tests, what he various testing kits do
Details / review of KEE electronic gold tester
Testing gold, specific gravity method