Testing precious metals with magnets
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CONTENTS
SILVER
GOLD
PLATINUM
COPPER / BRASS / BRONZE
GEMSTONES
OTHER EVERYDAY (SERIOUS) USES FOR MAGNETS
WHICH MAGNET?
SILVER
Silver is not magnetic, not even with the strongest magnet. However, silver is diamagnetic. If you hold a silver coin at 45 degrees a suitable magnet will slide down it slowly. This is because the moving magnet sets up an ‘electrical field’* that slows its fall. Now try it with a non-magnetic coin (most coins), the magnet, predictably, just ‘falls off’ the coin.
The diamagnetic test is good not only for coins but for any items with a flat (and reasonably smooth) surfaces, e.g. trays, boxes, plates and trays, even knives and forks. You need to tilt the item so that the magnet slides down, you cannot do this on curved or lumpy surfaces.
This is not a guarantee test for silver. Copper is also diamagnetic (though not as strongly as silver). Most silver plated items are made of silver-on-copper. So if a magnet 'sticks' to the item, it cannot be silver or copper. If a suitable magnet shows the diamagnetic effect the item might be silver (most likely with a coin) or it could be silver-plating on copper.
Do not confuse diamagnetism with magnetism. Many coins contain nickel and are most definitely magnetic, the magnet will 'stick' to the coin.
The QUICKTEST ‘magnet tester' for silver.
We supply three suitable magnets so that you can test any size of coin.
I say the magnets are ‘suitable’ because if a magnet is too heavy it won’t work and if it is too weak it won’t work. We have chosen three small but very powerful (neodymium) magnets. You get all three magnets, a copper coin** (98% copper) to test, a carrying pouch and instructions.
GOLD
Gold is not magnetic.
Pure gold (e.g. a bullion bar) is not magnetic.
Jewellery is made from a mixture (alloy) of gold and other metals. Varying the percentage (expressed as 'carat') of copper and silver results in yellow, red or pink gold – none of these are magnetic. White gold will contain silver, and maybe palladium (neither are magnetic), or nickel (which is magnetic, but the proportion of nickel will be very low). So no matter what the gold mixture (carat), you will not be able to detect gold with a magnet.
A magnet is useful for sorting scrap (we supply many magnets for this purpose). This is because gold is not magnetic. So start by removing everything that is magnetic – it will not be gold. But please remember: if an item is not magnetic, it does not mean it is gold, most metals are not magnetic.
PLATINUM
Generally platinum is not magnetic.
However, it depends on the platinum alloy: if the platinum is mixed with ruthenium, iridium or palladium then no, none of these are magnetic; if it’s mixed with cobalt then yes, cobalt is magnetic so, theoretically, platinum can be attracted by a very powerful magnet. This, in itself, does not mean the metal is platinum (many white metals are magnetic) but it does mean that you should carry out further tests and not automatically throw it away.
PLATINUM V. WHITE GOLD
If you have read everything above very carefully, you may have noticed that white gold can contain a small percentage of nickel and and platinum may contain a small percentage of cobalt - and both are magnetic. A magnet will not attract white gold but will (if powerful enough) attract platinum. That is because cobalt is three times more magnetic than nickel.
COPPER / BRASS / BRONZE
Copper is not magnetic. Brass is a mixture (alloy) of copper and mostly zinc (zinc is not magnetic). Bronze is a mixture (alloy) of mostly copper with about 12% tin, and sometimes small amounts of nickel (nickel can make it very slightly magnetic but, generally, bronze is not magnetic).
As with testing precious metals, a magnet will not tell you if an item is made of copper / brass / bronze, but it will tell you if it isn't.
For instance, you are an antiques dealer: copper cookware, brass door knobs and bed posts, bronze statues - if it's magnetic, it cannot be copper / brass / bronze.
GEMSTONES
Many text books still tell you that gemstones are not magnetic. It is true that you can't detect magnetism in gemstones with iron magnets, but you certainly can with the powerful neodymium magnets. Sort 'parcels' of stones (or alluvial sand) by sweeping the magnet across them, this will pick out the most magnetic (garnet) which will jump onto the magnet. You can also test garnet pendants by dangling the chain - place the magnet near the garnet, it will swing the chain. The effect with other stones is much weaker. Test a stone by placing it a small piece of foam, floating the foam on water, then see if the magnet will pull the stone/foam across the water.
In addition to testing cut gemstones, the magnetic test is useful for rough (uncut) gemstones (especially useful since optical tests are difficult or impossible with 'rough').
There is an entire website devoted to magnetism in gemstones, it's called Magnetism in Gemstones.
OTHER EVERYDAY (SERIOUS) USES FOR MAGNETS
The pretty fridge magnets you buy in gift shops are very annoying - fine for fixing two or three sheets of paper to your fridge, but after that they all slide off. Our neodymium magnets don't have pretty pictures on them, but they will hold an entire year-calendar firmly.
You are shopping for cookware for an induction hob. The salesmen like to sell the most expensive cookware. All you need to know is: is it magnetic? If it is magnetic, it will work with your induction hob.
Magnets can be 'fun' - children learn about what is magnetic, they love to play with magnets - and please do buy some from us if you want to amuse your children. But keep clear of neodymium magnets - the smaller magnets can be swallowed and the larger magnets are too powerful, they will cause injury when the child gets a finger caught between the magnet and a metal objects.
WHICH MAGNET?
* It’s actually a quantum mechanical effect, I have read about it, I do not understand it. The phenomena was discovered in 1778. In 2009 the Americans, using a super conducting magnet, levitated a mouse (the animal, not a computer mouse). The effect of a small magnet on a silver coin isn't this dramatic.
** The effect is stronger on silver, but we can’t afford to give away a silver coin with our magnetic tester.