Analysis of gold

Analysis of gold jewellery

Why do we need to analyze gold jewellery in modern times?

Gold jewellery is sold on basis of pure gold content of jewellery.

The analysis provides accurate information on content of gold (fineness) in jewellery with precision of 1 part per 1000 or in carats, where 24 carat gold is pure gold.

In many countries, there are laws determining which purity of jewellery may be sold and the allowable tolerance of gold in any jewellery. Some of these countries demand that every part of jewellery is tested (as it is in our country) or analyzed, and marked with suitable endorsement (stamp).

Definition of Analysis

Analysis is a professional term used for quantitative chemical analysis of materials, for  specific metal or chemical element for which there is an interest. The analysis is often associated with the analysis of ores and metals. In the context of gold, analysis is done to determine the share of gold in the metal.

The ancient Greeks knew three methods of quantitative analysis of gold and silver which are used even today. Stone with certain acids, fire assay cupellation and a method for determination of density are just some of them.

Fire assay cupellation - sample boiling at 1150 °C

Gold analysis techniques

Today in the modern world, there are several techniques of analysis but each of them is specific. This means that some analysis techniques damage the objects they analyse or may change its original shape, whereas other techniques do not damage the sample that is analyzed. There is also a question of working on the precision on individual techniques, how accurate (quantity of tolerance) is the result of analysis. Some of the methods not only get results such as the proportion of gold in some alloy, but they also determine the full composition of the alloy. The following table will briefly describe the precision of individual techniques.

We do the analysis using a technique called fire assay cupellation because it gives the most accurate results. We use this technique for jewellery that we make.

Fire assay cupellation is an ancient technique that was first described by Egyptian writings in 1360 BC and the technique is still used in the same way. This is the most accurate technique, which serves as a basic, standard technique by which all the other techniques are compared.

Fire assay cupellation complies with ISO standard 11426, whose license we hold. In general laboratories worldwide that analyse gold, use ISO standard 11426.

Fire assay cupellation

A technique of fire assay cupellation really depends on two measurements of the analytical balance (analytical balance 0.01 mg). The principle of analysis is based on the removal of all metal by oxidation (cupellation), after which, pure gold and silver alloy remains. The second step is removing silver with nitric acid. After this operation, pure gold remains, which is weighed on the analytical scales. The proportion of gold in the original alloy is given mathematically.