How to choose a diamond: the 4Cs explained

The 4Cs: the universal language of diamonds

When preparing to acquire a diamond, four fundamental criteria determine its value and beauty. Known as the 4Cs — Carat, Color, Clarity and Cut — these standards established by the Gemological Institute of America (GIA) in the 1950s constitute the universal vocabulary of diamond evaluation. Whether you are a seasoned collector or searching for your first stone, understanding these four pillars is essential for making an informed choice.

Before the 4C system, merchants used vague and often contradictory terms to describe diamonds. The introduction of this standard revolutionized global trade and offered buyers an objective framework for comparing stones, regardless of country or market.

Carat: more than just weight

The carat is the unit of measurement for a diamond's weight. One carat equals exactly 0.2 grams and is subdivided into 100 points. Thus, a 50-point diamond weighs 0.50 carats. This measure takes its name from the carob tree, whose remarkably uniform seeds once served as a reference for gem merchants.

The price per carat increases exponentially, not linearly, due to the growing rarity of large stones. A 2-carat diamond does not simply cost double a 1-carat stone — it can be worth three to four times more, as large rough crystals are considerably rarer in nature.

A perfectly cut one-carat diamond has a diameter of about 6.5 mm — barely larger than a lentil, yet capable of capturing all the light in the world.

Tips for optimizing carat value

Diamonds whose weight falls just below popular thresholds (0.90 ct instead of 1.00 ct, for example) often offer better value. The visual difference is imperceptible, but the savings can reach 15 to 20%. This strategy, well known to connoisseurs, allows you to invest the saved budget in cut quality.

Color: the quest for purity

The GIA color scale ranges from D (perfectly colorless) to Z (visible yellow or brown tint). The most prized diamonds are in the D to F range, considered colorless to the naked eye even under intense lighting. Stones in the G to J range, called "near-colorless," offer excellent value and are the preferred choice of savvy buyers.

It is important to note that this scale only concerns white diamonds. Fancy color diamonds — intense yellow, pink, blue or green — follow a completely different evaluation system where saturation and hue vivacity add value. An intense "Fancy Vivid Yellow" diamond can be worth far more than a white diamond of the same size.

The influence of setting on perceived color

The choice of setting metal significantly influences color perception. A G or H color diamond set in yellow gold will appear whiter than on platinum. Conversely, D-F diamonds reveal their full purity on a white gold or platinum setting, which adds no parasitic tint.

Clarity: reading inside the stone

Clarity evaluates the presence of internal inclusions and surface blemishes, observed under 10x magnification. The scale ranges from FL (Flawless, without any inclusion) to I3 (inclusions visible to the naked eye). Between these extremes, the grades IF, VVS1, VVS2, VS1, VS2, SI1 and SI2 offer a range of choices for every budget.

A VS1 or VS2 diamond often represents the best compromise between purity and price. At this level, inclusions are invisible to the naked eye and do not affect the stone's brilliance. Only a gemologist equipped with a loupe could detect them. For stones under one carat, even an SI1 grade can offer a perfectly clean appearance to the naked eye.

Every diamond carries within it a unique map of inclusions — like a mineral fingerprint forged in the depths of the Earth billions of years ago.

Cut: the soul of the diamond

Cut is arguably the most important of the 4Cs, as it determines the stone's brilliance, fire and scintillation. A perfectly cut diamond reflects light from one facet to another before sending it back through the top, creating that incomparable sparkle that makes diamonds magical.

The GIA evaluates cut across five grades: Excellent, Very Good, Good, Fair and Poor. Always prioritize an Excellent or Very Good grade, even if it means compromising on carat or color. A smaller but perfectly cut diamond will always be more beautiful than a large, poorly proportioned stone.

Different cut shapes

The round brilliant cut, with its 57 or 58 facets, remains the most popular and luminous. But fancy cuts — princess, cushion, emerald, pear, marquise, oval — offer distinct aesthetics and often better price-to-surface ratios. The emerald cut, for example, showcases clarity and purity with its broad step facets, while the cushion cut combines vintage charm with modern brilliance.

The choice of shape is primarily a matter of personal taste, but it also influences size perception and price per carat. At equal weight, shapes like oval or marquise appear larger than round, as they offer a greater surface area when viewed from above.