The root of the problem is many jewellers rely on acid tests to determine the authenticity and karat value of the item in question. Purchased for up to $50 per kit, acid tests are a common and accepted practice to help determine the approximate karat value of precious metals, such as gold. By their nature, these tests are qualitative and can have limited accuracy.
The test works by applying a series of acids—which are corrosive and require the jeweller wear special protection—to determine karat range, namely, those between 10-, 14-, 18-, and 22-karat gold. Based on the chemical reaction that takes place, or the lack thereof, the user may conclude the karat value of a jewellery item lies within a certain range (e.g. above 14-karat and below 18-karat). What the test does not reveal is the actual gold concentration, the existence and concentration of other precious metals, or whether the piece is gold-plated. The acid test is, to a certain degree, destructive, and by no means acceptable when evaluating high-value items, such as numismatic coins.
Typically priced between $100 to $1000, electronic precious metals testers are another tool jewellers commonly use. This technology measures the electrical conductivity of gold in a piece of jewellery and can serve as an indicator for its gold content. Although electronic testers can provide an answer quickly, they are limited to the types of precious metals that can be detected (i.e. typically gold and platinum) and may be less accurate with high-karat items. In addition, they may produce false results due to possible cross-contamination of the testing probe.
