How to Read the 4C of a Diamond, and Where to Look on the Certificate

Most people have come across the term 4C at some point. A certificate is a short list of letters and numbers, and it is not obvious how far any of it should be pushed. This article reads the 4C, the shared measure for diamonds used the world over, from the point of view of the person buying one.

Paying for a difference that appears on the certificate, or paying for a difference you can see on the hand. This article is written so that you can make that choice yourself.

• What the 4C are
• Color. How close to colorless
• Clarity. Whether inclusions are visible to the eye
• Cut. The one C decided by human hands
• Carat. A unit of weight, not of size
• Where to look on a certificate, and in what order
• Frequently asked questions

What the 4C are

The 4C are the international standard for assessing the quality of a diamond. Color, clarity, cut and carat weight. Each word begins with a C, which is where the name comes from. GIA, the American gemological institute, set the system out in the 1950s, and laboratories around the world now work to the same measure. Lab grown diamonds are graded on exactly the same 4C standard as mined stones.

One thing to say at the outset. The 4C are the common language of price, but they do not describe everything about beauty. Two stones with identical grades still look different in the hand.

So this article covers more than how to read a grading table. It is built around one question, which is where the line falls for the naked eye. Whether you pay for a difference on the certificate or for a difference you can see on your skin is yours to decide, and being able to decide it is, we think, the real value of knowing the 4C.

Color. How close to colorless

Color describes how close a stone is to colorless. On the scale set by GIA, D is the highest grade, and the letters run E, F, G and onward as the yellow tint grows stronger, ending at Z.

D, H, N and Z. The same shape of stone takes on more yellow as the grade descends.

From the buyer's point of view, the line sits between F and G. Up to F a stone is colorless, and from G it is near colorless. Graders, though, turn the diamond face down and set it beside master stones to judge the color.

Telling D from G by looking at a single stone face up is not easy even for a specialist. ANNA DIAMOND works only with F color and above because we hold to the colorless band while keeping the price within reason.

Clarity. Whether inclusions are visible to the eye

Clarity describes how few inclusions a stone holds inside it and how few marks it carries on the surface. From the top, the scale runs FL, IF, VVS1, VVS2, VS1, VS2, SI1, SI2 and then I1 to I3.

What matters is that this examination is carried out under ten times magnification. Most of the grading table therefore describes a world that only appears once the stone is enlarged.

From the buyer's point of view, the line falls between VS and SI. At VS and above, inclusions are essentially never visible to the naked eye. Put the other way, FL and VS look almost the same on the hand.

Whether that difference carries as much meaning as the difference in price is left to the person choosing. ANNA DIAMOND works only with VS and above, where inclusions cannot be seen by eye.

Cut. The one C decided by human hands

Color, clarity and carat weight are settled at the moment a stone forms. Cut is the exception.

At what proportions, and with what precision, the rough is polished. It is the only C in which human skill becomes the grade itself.

Cut is also what affects brilliance most. A stone whose proportions have slipped lets the light that enters escape through the bottom.

However good the color and clarity, light does not come back if the cut is poor. On the GIA scale there are five grades, from the top down: Excellent, Very Good, Good, Fair and Poor. IGI sometimes adds Ideal above Excellent.

Excellent is on the left, where light returns upward. ANNA DIAMOND works only with stones in that left hand state.

One thing we would rather say plainly. An overall cut grade is, as a rule, issued for the round brilliant cut alone. Shapes such as oval and pear often carry no overall grade at all.

An empty field does not mean lower quality. Where a cut grade exists, as it does for round brilliants, ANNA DIAMOND takes Excellent and above as the standard.

Carat. A unit of weight, not of size

Carat is often taken for a measure of size, though it is a measure of weight. One carat is 0.2 grams, a fifth of the weight of a one yen coin, which weighs exactly one gram.

The relation between weight and appearance holds a small surprise. Calculated at standard round brilliant proportions, the approximate diameter is 4.3mm at 0.3 carats, 5.2mm at 0.5 carats and 6.5mm at 1 carat.

Doubling the weight does not double the diameter seen from above. That is why picturing size from carat weight alone leaves a gap between the number and the stone in front of you.

The relation to price is worth knowing too. With mined diamonds in particular, large rough is scarce, so the price steps up sharply as carat weight rises. With lab grown diamonds that step is gentler, and the same budget reaches a larger stone. We go into the difference in price against mined stones in this article.

Where to look on a certificate, and in what order

That is how a certificate is read. To close, here is the range of stones we choose. Cut goes straight to brilliance and cannot be changed afterward, so we do not give ground on it, and for color and clarity we set the standard at the line where the eye can tell.

Frequently asked questions

If the 4C are the same, will every stone shine in the same way?

No. Even with identical grades, the position of the inclusions, the fluorescence and the finer points of the cut leave every stone looking a little different. The 4C are a common language for comparing prices, not a certificate of beauty. In the end we would suggest choosing by the light of the stone itself.

Can you see the difference between D color and F color?

Telling them apart by looking at a single stone face up is difficult even for a specialist. Grading is done with the stone face down, set beside master stones. On the hand, the difference shows far less than the difference in price.

I am unsure about quality when jewelry comes without a certificate.

Small stones, known in the trade as melee, are not issued individual certificates by long standing convention. ANNA DIAMOND provides an IGI certificate for every stone of 0.5 carats and above, and buys to a standard of F color and above and VS clarity and above, including the stones that come without one.

Are lab grown diamonds graded on the same 4C as mined diamonds?

They are assessed on the same measure. Laboratories such as IGI use the same D to Z color scale and the same FL to I clarity scale as they do for mined stones, and state clearly that the stone is laboratory grown.

What happens if I lose the certificate?

The value of the stone is not lost. With an IGI certificate, the contents can be looked up on the issuing laboratory's site using the report number. If the girdle is inscribed, the number itself remains on the stone.

After your purchase

ANNA DIAMOND offers returns within seven days, a two year quality guarantee, and free cleaning for life at our own store in Daikanyama. Payment in installments is available with no added fee.

You are welcome to see the stones in person

On paper, the difference between grades is a single letter. Brilliance, though, only becomes clear once a stone is resting on your hand. At the ANNA DIAMOND Gallery in Daikanyama, Tokyo, you can hold diamonds with IGI certificates and look at them for yourself. No appointment is needed.

For lab grown diamonds themselves, we explain the basics in our illustrated guide to lab grown diamonds.