The Acid Test

As well as beautiful vintage costume jewellery, there are many pieces of silver and gold in my SHOP. Both silver and gold hallmarks are often faked, confusing, or even absent from a given item of jewellery. For the sake of honesty and certainty, every item of precious metal I sell is fully tested before being listed. This post is about that process…

Silver
For this I use a vaguely named “silver testing acid”… It is a very effective and very simple test to carry out.

The acid is a transparent amber colour, and is dripped onto an item with a pipette. The second picture, above, shows what happens on a piece of steel (or any metal other than silver): no reaction, the solution remains transparent amber. The third picture shows what happens on a sterling silver ring: the result is an unmistakeable opaque blood red. After cleaning there will be left a dull grey mark on the silver (this is usually removable, read on)… There will be a similar, though slower and paler, reaction on silvers of a lower purity than sterling, and a faster and darker reaction on those above.

Gold
For this test I use two different acids (both are a mixture of nitric and hydrochloric). The first tests whether the item is gold (9ct or above) or not gold… The acid is clear and will react with non-gold metals, bubble fiercely and/or change colour. On gold there will be no reaction other than (on 9ct gold) a light brown stain left where the acid has been (this is removable, read on)…

The second picture, above, shows the acid on a non-gold item, as you can see it has bubbled up a vivid and quite pretty turquoise green colour. The third picture shows the result on 9ct gold – no reaction, the acid remains clear and still, leaving only a very faint brown tarnish.

Once I have confirmed that a piece is gold, of 9ct or higher, then the second acid is to work out the caratage. The test is carried out in the same way, though this acid will gently fizz a golden colour eventually, and again leave a faint brown stain. The golden fizzing is what you are timing. Basically the longer it takes to occur, the higher the carat of gold. Very approximately around a second per carat!  With practice it is possible to work out the purity of gold pretty accurately.

Plating
To make sure the item is solid silver or solid gold, and not plated, it needs to be filed into. This can be done with a tiny jewellery file in the most hidden place you can find on a given piece. Dust off any shavings and carry out the test again…

dscf4858Here is an example of a silver plated item – an opaque blood red result to the surface layer while the acid remains transparent amber on the filed area where a base metal is exposed. One should usually be neater with the acid, but this is a scrap piece and I needed enough to show in a photograph. On a gold plated item you would see bubbling/colour reaction on the filed area, with no reaction on the gold plating surrounding.

Notes

The acids should be handled carefully, they burn fingers and once ruined a nice pair of silk trousers which I had rather liked.

Tests should be carried out in daylight, a magnifying glass is helpful to see the reactions clearly.

Sometimes filing is enough – if it reveals any change in colour, i.e. copper, beneath the surface then you can be sure the item is plated.

Both the silver and gold testing acids will leave a faint mark on an item. I used to think these marks were permanent – most polishes do not remove them – but a very gentle rub with a little ‘Simichrome’ polish seems to do the trick.

And here are a few pretty things you can find in my SHOP….

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