Methods of testing gold (and other precious metals)
How to check gold.
Advice on testing gold, silver and platinum from the leading manufacturer of precious metal testers.
There is also a very good book on the subject.
Before you start, LOOK at the item. And if you cant see clearly, buy a good quality magnifier, it will be the best tester you ever own. All modern gold, silver and platinum items made in the U.K. or imported into the U.K. should be hallmarked.
Wall charts explaining hallmarks are shown (by law) wherever precious metals are bought or sold, familiarize yourself with these marks, its as important as being familiar with coins. Forged hallmarks (as with forged coins) exist but are rare, possibly because the authorities go to lengths to track down forgers, with a maximum penalty of seven years in jail.
No hallmark? Then start testing! The first two tests do not require acids.
Firstly, a magnet. Gold and silver are not magnetic. So if it's magnetic it can't be gold or silver. But NOT being magnetic doesn'tt 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.
Secondly, 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.
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.
Here are common questions I am asked about these acid testers.
Q. Do they work?
A. Yes. Mankind has been using the acid test for hundreds of years, it has even entered the English language, we say (referring to ultimate proof), "The acid test is..."
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 I HAVE to file the item?
A. Yes. There is no way of knowing if the item is thickly plated unless you file the surface to test underneath, so if you can't file it you can't test it. Incidentally, even electronic testers cannot test through plating (unless the plating is very thin).
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 household cleaners, you may wish to wear an apron to protect clothes (in a shop, it looks really impressive if you wear a lab. coat). Small drops of acid stain small spots of skin yellow (if youre 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). Full safety instructions come with every kit and every bottle, please read them.
Q. I am colour-blind, how will I see the colour-change of the acid?
A. I'm red-green colour-blind and I have included special instructions explaining what the "colour change" looks like to me, our acids do not require you to see the difference between green, brown and grey! Total colour-blindness is extremely rare and is associated with more serious eye conditions (if you think you are totally colour blind, see your optician).
ELECTRONIC GOLD TESTERS...AND OTHER METHODS
Low-cost electronic testers vary in price from under £150.00 to about £500.00. The cheapest use a strong acid as a contact fluid and are not accurate; the best is the KEE tester.
Melt-and-Assay (Fire Assay). Melt the item (or part of it - if only a fraction of a gram). The service costs (if we get it done for you) £95.00 and takes two to 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, and it's up to you where to sell it (there are many tips in The Gold & Silver Buyer's Handbook).
ICP (Inductively-coupled plasma mass spectrometry). 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. Prices from about £35,000.00, but what you get is a laboratory set-up, not a 'device'. We do not sell these.