When buying jewellery, most customers mainly focus on its design, price or the size of the gemstone. Hallmarks and certificates often receive less attention, even though they confirm the authenticity of the materials used and can tell us a lot about the quality of a gemstone.

The Czech Republic has one of the best systems for controlling precious metals in Europe, which gives customers a high level of protection when buying jewellery. However, many people still do not know what the different marks mean or how to read a certificate correctly. So, let’s look at what you should pay attention to when buying jewellery.

Hallmarks Are the First Guarantee of a Precious Metal’s Authenticity

The first thing I recommend checking when buying jewellery is the hallmark issued by the Czech Assay Office. It confirms that the precious metal has been officially tested and meets the stated purity standard.

On a piece of jewellery, you will most commonly find:

• a hallmark confirming the officially verified purity,
• a purity mark, for example 585 for 14-carat gold or 925 for sterling silver,
• a maker’s or responsibility mark identifying the manufacturer or importer.

However, not every piece of jewellery is legally required to have a hallmark. Hallmarking is required for gold and platinum jewellery weighing more than 0.5 g and for silver jewellery weighing more than 3 g. This means that delicate earrings, small pendants or thin chains may be completely fine even without an official hallmark. A reliable jeweller should always be able to explain what the individual marks mean and provide information about the origin of the materials used.

Certificates Confirm the Characteristics of a Gemstone

If a piece of jewellery contains a diamond or another valuable gemstone, a gemological certificate also plays an important role. It is issued by an independent laboratory that objectively examines and describes the characteristics of the stone.

Some of the most respected laboratories include GIA (Gemological Institute of America), IGI (International Gemological Institute) and, in the Czech Republic, ČGL (Czech Gemological Laboratory).

Each certificate has a unique identification number, which can usually be verified online. On some diamonds, this number is also laser-inscribed directly on the girdle of the stone.

It is important to know that diamonds and coloured gemstones are certified differently. Diamonds are graded according to the international 4Cs system, while certificates for sapphires, rubies and emeralds mainly focus on the type of mineral, whether the stone is natural, possible treatments and, in some cases, its geographical origin.

How to Read a Diamond and Gemstone Certificate

Many customers look only at the number of carats when they see a diamond certificate. In reality, weight is only one of many characteristics that determine the value and beauty of a diamond.

Diamonds are graded worldwide using the 4Cs system, created by the Gemological Institute of America (GIA) and now used by most respected gemological laboratories. This system makes it possible to compare diamonds objectively.

On a diamond certificate, pay particular attention to the following information:

• Carat (Ct) – shows the weight of the diamond. A higher number of carats means greater weight, but it does not automatically mean higher quality or a more beautiful stone.
• Color – describes the colour of the diamond. The scale starts with D, which represents completely colourless diamonds, and continues to Z, where a yellowish tone is clearly visible.
• Clarity – describes the purity of the diamond based on the number, size and position of natural inclusions and other internal or surface characteristics.
• Cut – evaluates the quality of the diamond’s cut. The cut has a major influence on how the diamond reflects light and how much it sparkles. Even a smaller diamond with an excellent cut can look much more beautiful than a larger stone with an average cut.

A certificate usually also includes several other characteristics:

• Polish – evaluates how well the individual facets of the diamond have been polished. Well-polished facets allow light to travel through and reflect from the stone more effectively.
• Symmetry – describes how precisely and evenly the individual facets are cut. Better symmetry helps the diamond interact with light and gives it a more lively appearance.
• Fluorescence – describes how the diamond reacts to ultraviolet light. In most cases, it does not have a major effect on everyday wear, although it can slightly influence the appearance of some stones.
• Laser Inscription – some diamonds have their certificate number laser-inscribed on the girdle. This makes it easier to check that the certificate really belongs to the specific diamond.

High-quality certificates often also include a Clarity Plot, which is a diagram showing the position of inclusions inside the diamond. It works like a unique “fingerprint” of the stone and helps confirm that the diamond matches its certificate.

Certificates for Coloured Gemstones

The 4Cs system is not used for coloured gemstones in the same way as it is for diamonds. Their certificates mainly focus on confirming the type of mineral, whether the stone is natural, its weight and dimensions, and especially whether it has received any treatments.

The most common treatments include:

• Heat Treatment – commonly used for gemstones such as sapphires and rubies to improve their colour or clarity. It is a standard and widely accepted treatment.
• Oil Treatment – mainly used for emeralds. Oil fills small fractures in the stone, making it appear clearer.
• Fracture Filling – fractures in the gemstone are filled with a special substance or glass.

Other enhancement methods, such as diffusion treatments or impregnation, can change the appearance of a gemstone and may have different effects on its value. A high-quality certificate should always clearly state whether the gemstone has been treated and what type of treatment was used.

A Certificate Is Important, but It Is Not the Only Sign of Quality

A hallmark and a certificate provide important reassurance, but they do not guarantee the quality of the entire piece of jewellery. For example, a certificate does not tell you anything about the quality of the craftsmanship, how securely the gemstone is set or what level of after-sales service the jeweller provides.

Our family has been working with precious metals and gemstones for more than 50 years, and during that time we have learned one important thing – the most valuable certificate is the customer’s trust. That is why we also recommend looking at the services offered by the jewellery store. Does it provide jewellery cleaning, repairs, ring resizing or regular jewellery inspections?

The best jewellers do not disappear once the customer has paid. They take care of both the jewellery and its owner in the long term. Good after-sales service is therefore one of the best signs of a reliable jeweller.