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 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. must 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,
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. And some some platinum is magnetic. We have a large range of magnets.
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. It doesn't matter which shape of file you use but we suggest you buy a few because they wear out.
THE ACID TEST
You've tried all of the above, you may have your suspicions, but now you need absolute proof: the acid test (this is where expression the acid test comes from).
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, (there is also detailed information with each product description).
This is what you do:
File the surface (a fine needle- file is included with each set). Do this firmly but only over a small area, and in a place it won't show (eg the inside of a ring shank, the back of a brooch, the clasp of a chain). This is to ensure that you are testing the item underneath any plating. Put a 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). There are also acids to test for silver, platinum, Palladium and steel.
An alternative to using a needle-file is to use a steel scraper and scrape (scratch*) the surface, see . This advanced method takes more skill than using a file, read about how this works.
* This is the origin of the expression, coming up to scratch.
Another advanced method uses a touchstone instead of putting the acid directly onto the item. There is a simple (relatively!) method using a touchstone and samples (test-needles) supplied by Quicktest; you can also (just out of interest) can see the advanced method used at the Birmingham Assay office.
For GOLD, acids are designed to test to the nearest carat commonly used in jewellery (in the UK, 9ct, 14ct 18ct, 22ct) but, with practice, results to within 5% can be achieved. SILVER: in addition to non-silver you can distinguish Sterling (.925), 'low-grade' (.800) and (just about) very low grade (.500) silver.
If you have decided to buy a TROYTEST or QUICKTEST testing set and what to know more, you may wish to skip the rest of this article and go to Guide to chemical testers (gold-testing acids)
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 also file the item before carrying out a test an electronic tester (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 cloth or polishing sticks.
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). You can read about other safety equipment and what we do, and don't, recommend.
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.
DE-PLATING
This is the most common type of 'low-cost' (£300.00 to £600.00) 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, not very accurate on white metals (including white gold), 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: they all require a contact liquid or gel, with most makes this is a salt solution (safe) but some use an acid. 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 to £500.00). Cost of consumables: the 'pen-probes' with the salt solution lasts a few hundred tests, replacements are about £50.00. Availability: we sell the best model, the KEE tester.
XRF (X-ray Fluorescence)
How they work: they fire x-rays a fraction of a millimetre into the item and see if it 'glows' (fluoresces). A display lists the percentage of all the metals; in the sample, not just the precious Metals! Ease-of-use: reasonably easy to use. Within a few seconds it gives an approximate result, a detailed analysis take a minute or two. 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 underneath. 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 in the last few years, now as low as £10,000.00 for the handheld models, up to £40.000 for the 'cabinet' models. Cost of consumables: there are 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 costs between £1500.00 and £2500.00. Cost of consumables: none, just water plus, maybe, batteries for your balance. Availability: we have the MD-200S by Mirage on special offer.
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 weigh it; if the diameter, thickness and weight are correct, then it's made of 22ct gold.
RESISTIVITY
How they work: measures the electrical resistance through a metal. Ease-of-use: (don't know, never used one!). Limitations: 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. With the cheaper models (just a few hundred pounds) you must measure the dimensions very accurately with a micrometre. The advanced models (£1500.00 to £2000.00) help you measure the dimensions as part of the process, and they have a built-in database of common items which includes the measurements. Safety: safe. Cost: £500.00 to £2000.00 as above. Availability: we do not 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: (not sure, we've never used one). These are standard testers in the world of engineering, e.g. to see if steel is rusting or concrete is corroding, but when used for precious metals it requires specialist software to translate the reading into something meaningful. Limitations: it will readily show if an item is not homogenous but it won't tell you what the item is made of (e.g. gold). Safety: safe (the same 'sound waves' as used in ante-natal testing). Cost: £750.00 to £1000.00. Availability: we do not sell these.
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 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,
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