How to recognize a quality diamond? By 4C rating

And what are the 4Cs of a diamond? 

• Color, 

• Clarity, 

• Cut,

• Carat.

Although not all criteria can be observed with the eye, they have a major impact on the appearance and price of a diamond. Even a slight difference in colour or clarity can mean an order of magnitude different value. That's why it's a good idea to be at least familiar with the internationally recognised grading system – whether you're planning to buy an investment diamond, a diamond engagement ring or just want to treat yourself to some unique diamond jewellery. 

Weight

The first of the "four C's" indicates the weight of the diamond. This is measured in carats (ct), with 1 carat corresponding to exactly 0.2 grams. The carat may be the most well-known measurement, but it's far from the only one that determines the value of a stone – it's simply one piece of the puzzle.

To determine the carat weight of a diamond, special jewellery scales are used that can weigh to three decimal places. The resulting weight is then rounded according to strict rules – for example, a 0.999 ct diamond can be rounded to 1.00 ct, but a 0.998 ct diamond can only be rounded to 0.99 ct.

In some cases, such as round brilliant diamonds, the weight can be estimated without scales – based on the diameter of the stone and the known proportions of the cut. Nevertheless, weighing on a laboratory balance remains the most accurate way of measuring.

Interestingly, the price does not increase uniformly with weight. The larger the stone, the rarer – and the steeper the price rises. So a 2 ct diamond is much more valuable than two one-carat stones combined.

MIALIS NOTE: Be careful – do not confuse a metric carat (ct) with a carat (kt). The kt is used exclusively to express the purity of gold and other precious metals

Cut

Cut is also one of the most important criteria affecting the overall appearance of a diamond. Unlike the other characteristics that a diamond acquires during its natural formation, the cut is the result of human labour. A well-crafted cut allows the stone to make the most of the incident light and enhance its sparkle, shimmer and brilliance. The cut is evaluated based on precise proportions, symmetry and quality of polish, and diamonds are classified into five basic grades based on the result.

Grades

1. Excellent / Ideal cut 

• Diamonds of the highest quality, only about 3% of all diamond production .

• They reflect almost all incident light.

2. Very good

• Very well made cut.

• Reflects most of the incident light.

• The untrained eye cannot tell the difference from a grade 1.

3. Good

• Diamonds of this type reflect most light.

• This grade accounts for a quarter of all production. 

4. Fair

• Well cut diamonds still fall into this grade.

• Less sparkle due to less light reflection.

5. Poor

• They do not meet the requirements for a quality cut.

• Diamonds have almost no sparkle, most of the light is lost on impact.

A quality cut will enhance both the sparkle and the value of the diamond – so it pays to watch the rating as well as the colour or clarity. 

HOW IS IT IN MIALIS? Most often we use diamonds rated Excellent and Very good, rarely Good. You certainly won't find Fair or Poor cuts in our jewellery.

​​The GIA colour scale

To determine colourlessness, the most commonly used scale is the one developed by the Gemological Institute of America (GIA). This is a scale from D-Z, with D representing the perfectly colourless variant – but this is extremely rare. As the letter of the scale increases, the intensity of colour increases and the value of the stone usually decreases.

The GIA colourlessness scale is divided into 5 categories:

D-F: colourless, most valuable and rarest diamonds.

G-H: almost colourless, but still looks clear in everyday jewellery.

I-J: considerable colour, more suitable for setting in yellow gold where the colour is lost.

K-M: the yellow tone is clearly visible, lower price category.

N-Z: coloured diamonds with a yellow to yellow-brown tinge, more affordable but less prized.

HOW IS IT IN MIALIS? Most often you will find jewellery with diamonds in G or D-F colour. But if you have specific color requirements, we can find and offer more variations.

Methods of determining colourlessness

1. Visual comparison 

The most common method is visual comparison with reference stones, the so-called master stones. These usually represent real diamonds with a minimum weight of 0.7 ct and a clarity of at least VS. Their degree of colourlessness is predetermined and it is by comparison that gemologists analyse the colourlessness of the diamond under examination. The process takes place under standardised lighting conditions, often under a lamp simulating daylight.

2. Electronic colorimeters

Electronic colorimeters are used to determine colorlessness more accurately, especially for diamonds set in jewelry where the color of the metal can affect the actual hue of the stone. These instruments measure colorlessness objectively and help eliminate subjective mistakes of the human eye.

3. Colored diamond comparison systems

There are also colored diamonds where it is the natural striking color that is desired. They are called fancy diamonds and have a distinctive coloration outside the usual D-Z scale. Special grading systems are used to determine the colour of fancy diamonds. These allow accurate determination of hue, saturation and colour saturation. Here, the more intense and saturated the shade of yellow, pink or even green, the more valuable the gemstone.

Clarity

The last evaluation criterion is cleanliness. Gemologists look for the presence of inclusions, which are formed during the natural formation of the diamond. Inclusions are considered flaws and reduce the value of the stone. They are classified not only by their quantity and position, but also by the shapes they resemble: crystals, chips, bruises, cavities, pinpoints, clouds, twinning wisps, feathers, needles, knots, grain centers.

The purity assessment is done at 10x magnification using a special magnifying glass or microscope. It is estimated whether the defects are visible at this magnification, how pronounced they are, how they affect the appearance of the stone and whether they can be observed with the human eye. On the basis of this information, the diamond is classified into one of the clarity grades, most often according to the GIA scale.

MIALIS NOTE: To make things not so simple, inclusions are not always necessarily a "flaw", for example, in salt and pepper diamonds or moss agates they are considered beautiful imperfections that make the gems more interesting and original.

Diamond clarity grades

• Flawless: no internal or surface imperfections, even at 10x magnification, rare.

• Internally Flawless (IF) / Loup Clean (LC): no internal imperfections, even at 10x magnification, there may be minor surface flaws that are not considered major. This is the highest grade used in the jewellery industry.

• Very Very Small (VVS1, VVS2): very, very small inclusions that are very difficult to detect at 10x magnification, even for an experienced professional.

• Very Small (VS1, VS2): very small, but a little easier to spot when using a magnifying glass, but not detectable to the eye of the casual observer.

• Small Inclusions (SI1, SI2): small inclusions, clearly identifiable under magnification, but usually not visible to the casual observer from the top of the diamond.

• Included 1 (I1) / Piqué 1 (P1): moderately prominent inclusions, visible under a magnifying glass and may be perceptible to the naked eye under certain circumstances.

• Included 2 (I2) / Piqué 2 (P2): distinct and more numerous inclusions, normally visible to the naked eye, may reduce the brilliance and optical clarity of the stone.

• Included 3 (I3) / Piqué 3 (P3): Inclusions are extensive and highly visible without the use of a magnifying glass, often significantly affecting the brilliance and appearance of the diamond.

HOW IS IT IN MIALIS? The most common diamonds in our studio are those with clarity grades SI1-S12 or VS1-VS2. We pride ourselves on quality, which is why you won't find lower grades with the letter I in our diamonds. However, if you have clear clarity requirements, we would be happy to offer you other options.

Bet on the proven

Now you know that the value of a diamond doesn't depend on size alone and you know the 4C's. The four main criteria. In practice, the fifth C - certificate, the certificate of authenticity - is also often used. This is issued by recognised gemological laboratories and ensures that the diamond actually matches the stated parameters.