It is easy to know what metal a piece of jewellery is made of if it is hallmarked or has the gold purity stamped on it. However, so much jewellery is not marked at all and so a seller has to ‘test’ the piece to determine what it is made of. How have they tested the piece and how reliable is this testing? Well, for jewellery sellers, there are two main ways of testing the quality and content of the metal. The first method is acid testing, the second uses electronic testers. There are other methods such as x-rays, but they require use of a laboratory, and some destructive tests such as fire assay but they can damage the jewellery.
Acid testing, as the name suggests, involves the use of acids. A photo of an acid testing kit is shown at the top of the post. It is a box containing different bottle containing acids, plus a black testing stone. The bottles are labelled 9kt, 14kt, 18kt, 22kt, silver and platinum. Let’s say we are testing for gold, then the piece of jewellery to be tested is swiped across the testing stone, leaving a metal sample. Then a drop of acid from the 9kt bottle is placed on the metal sample. If it dissolves the metal of the sample, this means that the gold is of a higher quality, so you then need to test for 14kt gold, and so on, until the acid dissolves the metal sample.
Electronic metal testers, which are battery operated, don’t use acids but most use some form of testing gels. The prices vary quite a bit. Some only test for gold, either yellow, rose and white gold, while some also offer silver testers as well.
None are made in Australia which makes it very difficult if a problem occurs and it needs repair. They are generally quite easy to use and it is good not to be using acids.
The pieces of jewellery that remain a problem with all testing methods described here is identifying gold that is is rolled gold, gold filled or gold plated. If the layer of gold is thin, the testers may pick the underlying metal up but if it is a thicker external gold layer, the testers will only pick up the gold layer. You need to file down through the gold layer to do a proper test but this can be destructive to the piece which you want to avoid.