SUMMARY:

• 1) Gold density and carat: two fundamental indices
• 2) The composition of gold: various alloys, colors and chemical reactions
• 3) How can you tell if a coin is made of gold?

Given its physical and chemical properties, how can you tell if the object you're holding is really gold? Whether it's junk jewelry, gilding, plating or alloys, it can be hard to tell.

There are, however, several objective criteria that ensure reliable identification of gold: its density, its chemical composition, but also certain simple tests for coins and jewelry.

1) Gold density and carat: two fundamental clues

Gold density analysis. One of the most effective methods is to analyze the density of the precious metal. This is known as "density", a physical quantity that characterizes the mass of a material per unit volume.

This mass is precisely 19.32g/cm³ for pure 24-carat gold. By way of analogy, one liter of gold weighs the equivalent of 19.3 kilograms.

This level of density makes it a difficult material to counterfeit. In fact, gold has a much higher density than most metals. For comparison:

Technically, there are several methods for estimating this density, such as hydrostatic weighing. In this case :

• the metal or object is weighed dry
• A second weighing is carried out, this time immersed in water.
• The two results are used to calculate density = dry weight / (dry weight - immersed weight).

The result obtained will enable you to quickly detect whether the metal or object under analysis is a counterfeit made with less dense metals.

Please note: gold test kits are available from jewellers or on the Internet, enabling you to test the purity of your gold yourself.

The carat as a measure of purity

This term, which comes from the Greek "keration", is a globally recognized unit of measurement for determining the quality or, more precisely, the purity of gold.

Today, the carat measures the quantity of pure gold present in an alloy, expressed in 24 equal parts. One carat represents 1/24th of the total mass of an alloy. This makes it possible to distinguish several degrees of gold purity:

- Pure" gold, i.e. unmixed, is equivalent to 24 carats. Jewelry made from 24-carat gold is rare, as it is fragile and therefore unsuitable for everyday wear.

- 18-carat gold therefore contains 18 parts pure gold and 6 parts other metals (copper, silver, nickel, palladium, etc.). This represents a gold purity of 75%. This 18/6 blend is widely used in jewelry.

- 14-carat gold therefore represents a purity of 58.5% gold.

- A 9-carat gold therefore represents a purity of 37.5% gold.

After analysis, the carat also makes it possible to determine the value of gold for purchase or resale. Logically, the purer the gold, the higher its value. For this reason, it is imperative to check the official carat value when purchasing precious objects, to ensure their authenticity and fair market value.

For your information, ingots and jewels are generally stamped with the words "750". In concrete terms, this means the presence of 750 ‰ gold, or 18 carats. This marking is made when the jewel is manufactured.

2) The composition of gold: various alloys, colors and chemical reactions

Given the above, it's clear that the lower the carats, the higher the alloy content. Mixing pure and alloyed gold is a very common practice in the jewelry industry.

In fact, pure gold is too malleable, making it impractical for the manufacture of jewelry worn on a daily or regular basis. The use of alloys will modify the appearance and properties of the object. A solution that enhances strength and scratch resistance, for example.

The different types of alloys on the market

Among the alloys most commonly used in combination with pure gold are :

• Silver
• Nickel or palladium
• copper

The result of these different mixtures of gold and alloys is gold jewelry of varying hues.

Please note: when we commonly speak of "gold-plated", we are in fact referring to a base metal to which a thin layer of gold has been applied. The market value of such a product is incomparable to that of gold jewelry.

Chemical tests to assess the presence of gold

Given the variety of gold jewelry and objects available, it's easy to wonder about the reliability, traceability and quality of what you're buying. Nevertheless, there are several ways to check whether an object or piece of jewelry is made of gold.

These include :

- (As mentioned above) A gold purity test is possible.

- The use of touchstones on which the desired object is rubbed. An acid is then applied to analyze the chemical reaction.

- Nitric acid is used to determine whether the object is gold or another metal. Gold is not sensitive to this acid, so there should be no reaction.

Of course, these tests are not 100% reliable. Our precious metals professionals can provide you with the best possible support and a real guarantee of precious metal quality.

3) How do you know if a coin is gold?

When you call on the services of a gold and precious metals professional, accustomed to handling bullion and bullion coins, he or she will bring to bear his or her expertise based on a number of visual, tactile and technical methods.

Indeed, identifying a gold coin, such as a Louis d'Or, a Krugerrand or a 20 Francs Suisse, requires real know-how and the use of very specific tools.

A meticulous visual examination

It is important to note the presence of a hallmark attesting to the gold content. In France, there are several possible hallmarks:

• The seahorse symbol signifies 24-carat or 999 thousandths gold.
• The symbol of an eagle's head 1 or Coq Premier Titre for 22-carat gold or 916 thousandths.
• Tête d'aigle3, Coq3 symbol for 18-carat or 750 thousandths gold.
• The scallop symbol for 14-carat or 585 thousandths gold.
• The trefoil symbol for 9-carat or 375 thousandths gold.

Other elements to be checked include color homogeneity, absence of wear, and absence of oxidation of the analyzed gold metal.

For coins, additional verification points are required, such as the well-defined relief of the graphic, the standardized diameter and the exact weight of the coin. For example: