What is a touchstone ?

Determining the selling price of gold jewelry depends on the title of the object. Indeed, depending on the purity of the product, bracelets or rings do not have the same value. It is for this reason that gold buying companies and jewelers seek to estimate the exact composition of the product. There is a simple solution to determine if a piece of jewelry is 18 carat gold.

The touchstone is actually made of jasper, a hard stone. It has the particularity of attaching traces of gold, and of not reacting to the acids used. Thus, you can know the alloy of the jewel with quite great precision.

However, precautions should be taken throughout use. The composition of the product is determined using an acid, or more precisely aqua regia. Aqua regia is a mixture of nitric acid and hydrochloric acid.

The first appearance of the touchstone dates back to Antiquity. This touchau method appears regularly in specialized literature in the Middle Ages and the 19th century. It experienced a particular expansion in the 15th century, to fight against fake jewelry. Even today, it is used to know the title of an object supposedly made of gold.

Other methods have been tried over the years, including the cup test, but the touchstone allows reliable results to be obtained quickly and simply.

Nowadays, jewelers can also weigh objects, with specially calibrated scales. But the touchau method still remains valid in title control offices.

The acid used with the touchstone is a mixture of nitric acid and hydrochloric acid. This association is more commonly called “eau regia”. Its oxidation properties guarantee dissolution of all non-precious metals, but also gold, under certain conditions. This is why the alloy of acids is precise, to guarantee the most accurate measurement.

The quantities of acids to be respected are:

• 18 carat gold test: 2 to 4 for 1 volume of nitric acid;
• Gold test greater than 14 carats: 49 to 1, with the addition of distilled water;
• Gold test less than 14 carats: pure nitric acid.

On contact with acid, the gold will react and change color. Depending on the shade, it is possible to determine the purity of the metal. In the case where the gold does not vary, it can be assumed that the fineness is greater than 18 carats. The more the color changes, the weaker the title. Finally, if the gold completely disappears, this means that your jewelry does not contain gold at all.

The touchstone is part of a kit, including a jasper fragment and accessories (acids). Each time, the acid contents are separated into different bottles, to facilitate use and testing.

Using the touchstone follows several steps. To begin, the tester places the jasper flat on a table. Then, the professional or individual rubs the object to be tested, in order to leave a mark on the stone. All types of products can be rubbed: diamond rings, drills, etc. Then, you must delicately apply a few drops of acid and observe the reaction. The reaction may cause a color change, which then indicates an estimate of the titer. The use of aqua regia must be done with caution. Good to know: you must seek medical advice after any contact with skin or eyes.

Gold Union specializes in the purchase of gold and the sale of gold bars and silver. You can now contact an advisor to find out about the entire range of investment bars and gold coins. The presentation of references can take place in agency, or via our e-commerce site.