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The Essential 7C's
Instead of grams or kilos, diamonds are weighed in carats (not to be confused with gold’s Karat which signifies purity). This simply denotes a measuring scale where each 1 carat = 0.2 grams (0.50 carat = 0.1 gram and 5 carats = 1 gram).
1. The carat
As the carat weight increases, so does the size of a diamond. However, confusingly, this relationship is not a linear but rather a curve - so a 2.0ct diamond will not appear twice as big as a 1.0ct diamond.
Expert Tip 1
When comparing similar diamonds try to look at the measurements. Some diamonds with similar weights can vary significantly in measurements. Pick the one with wider measurements, and you will gaina larger diamond surface area for the same value.
Expert Tip 2
Certain diamond sizes are highly sought after (e.g. 0.50ct, 0.75ct, 1.0ct) and prices can vary dramatically depending on the carat weight. A 0.90ct diamond can be 10-20% better value than a 1.0ct diamond of the same quality but can appear almost identical in size but very different in price.
HISTORY & BACKGROUND
The term carat originates from the Greek and Arabic names for the carob tree - Keration in Greek and Qirrat in Arabic. The dried seeds of the Carob (or Locust) tree were once widely used by trading merchants as counterweights for weighing gold, diamonds, gemstones and pearls due to their relatively consistent weight and size. It is important to note however, that the term “carat” with reference diamonds is different to “karat” which is the value used for the purity of gold.
The Byzantine era used glass pebbles, based on carob seeds, for weighing coins, which weighed in at 196 mg, consistent with the average weight of an individual carob seed. However their use eventually diminished as it was discovered that despite their visual uniformity, the seeds were not actually consistent in weight. Many attempts were made to standardise the measurement of gemstone weight and it was only in 1907, at the Fourth General Conference on Weights and Measures that the “carat” was adopted as the official metric measurement for gemstone weights.
In 1913 the United States officially accepted the ‘carat’ as the gemstone measurement, and in 1914 the United Kingdom and Europe followed suit. By the 1930s, the majority of the diamond and gemstone industry had agreed to the standardised measurement, which is still in use today.
Dimensions play an important role in the appearance of a diamond. In addition to the carat weight, the distance across the top of the diamond must also be taken into consideration. A common misconception is that half a carat is half the size of one carat. In fact, a half carat is half the weight of one carat, but the millimetre difference on a round stone is only 1.35mm. The average measurement for a 0.50ct stone is 5.00mm, while the average 1.00ct stone measures at 6.35mm.
While carat weight may indicate a diamond’s size, the shape and cut of a stone also play a large part in determining how large or small the stone appears. An elongated shape such as the Marquise cut may appear larger than a rounded shape such as the round brilliant even if the two stones share the same weight.
When comparing two stones of the same shape however, it is important to look at the cut grades and table and depth percentages, as shallower stones will tend to appear larger than deeper ones. Other aspects such as girdle width can also affect how large a stone appears, while not necessarily affecting the quality of the stone.
2. The color
Diamond colour is graded according to the GIA colour scale, from D to Z. D is rated the most colourless, and therefore the most sought after and costly.
For white or colourless diamonds (as opposed to coloured diamonds, which is a whole different story), the diamond industry has adopted an alphabetical colour scale from D to Z, with D as the highest grading. As you go down the scale, the diamond starts to develop a yellow or brown tint.
Experts in the world of diamonds determine the colour by comparing a diamond against a master set of diamonds of different colours. Without comparing diamonds side by side, it is very difficult to see the difference between a D and a G.
Completely colourless diamonds (such as D and E) are much rarer than others which is why they come with a higher pricing premium. The key question is always where to draw the line when choosing the colour of a diamond - how far can you compromise colour before the diamond is too tinted? The answer to this question is relative to your budget and quality expectations.
Expert Tip 1
For colourless diamonds the differences between D to G are barely visible but can offer 20 to 40% better value. D is generally more for the investor or diamond connoisseur.
Expert Tip 2
H graded diamonds are often considered on the border between premium colourless and tinted diamonds, and therefore offer great value without any visible yellow or brown tint unless compared side by side with a whiter diamond.
Expert Tip 3
I and J colours will generally face up white from the top, but you will be able to detect slight yellow or brown tints when viewed from multiple angles. CaratGlow highly recommend staying with GIA only for these colour grades, as any other certificate in this range is likely to fall below your colour expectations.
Expert Tip 4
K and L are acceptable on a GIA certificate in terms of tint if that major compromise is needed to reach size within a budget. CaratGlow strongly recommend setting these diamonds in Yellow or Rose Gold jewellery to make the diamond appear less tinted.
D is the highest colour grade attributed to a diamond, denoting that the stone is completely colourless (white); as such, they are extremely rare and command the highest prices.
The colour difference between a D and an E graded stone is usually only visible to an expert gemmologist using master stones as a comparison, although E graded stones are slightly cheaper.
The colour difference between an E and an F is only visible to an expert gemmologist using master stones as a comparison. F grades are the lowest and therefore least expensive of the premium colours.
G graded diamonds are nearly colourless and a slight colour difference only become perceptible when compared to diamonds of grades D or E. G stones appear colourless especially once set and therefore offer excellent value for money.
H coloured diamonds are near colourless diamonds which still appear totally white or colourless if they are not compared side by side with higher colour graded stones. The H colour is generally considered the watershed between colourless diamonds and slightly tinted diamonds.
I coloured diamonds are very slightly tinted diamonds, however, once set in jewellery, these stones may appear colourless. If you are looking to maximize your budget, then an I coloured diamond offers great value for money.
J coloured diamonds are very slightly tinted diamonds, however, once set in jewellery, especially in yellow gold, it is harder to see the slight yellow tint which the J grade produces.
K coloured diamonds are slightly tinted diamonds, however, once set in jewellery, especially in yellow gold, it is harder to see the slight yellow tint which the K grade produces.
Seventy Seven Diamonds currently offers only stones in the higher range of D-J, as these are the only grades we recommend, however, lower clarity grades can be made available on special request.
3. The Clarity
When diamonds are formed, deep underground and under extreme pressure and heat, imperfections in the crystal structure can form and mineral impurities become trapped inside the stone.
The size of these impurities and imperfections determine the clarity grading of a diamond. Diamonds without such impurities are very rare.
The grading scale starts from Flawless / Internally Flawless (FL/IF), Very Very Slightly Included (VVS1/VVS2), Very Slightly Included (VS1/VS2), Slightly Included (SI1/SI2) to Included (I1, I2 and I3). 77 Diamonds does not sell diamonds below SI2 as they are not considered suitable for jewellery. Generally, diamonds below a VS2 grading are likely to have visible inclusions to the naked eye however this is on a stone by stone basis.
Clarity IF Image Internationally Flawless: These rare high clarity diamonds are 100% flawless inside the diamond with no blemishes or inclusions.
Clarity VVS1 Image Very Very Slightly Included 1: There will be one minor inclusion within a diamond of this grade but only visible under 20x magnification or more.
Clarity VVS2 Image Very Very Slightly Included 2: There will be minor inclusions within a diamond of this grade but only visible under 20x magnification or more.
Clarity VS1 Image Very Slightly Included 1: Diamonds of this clarity will have several inclusions that are only visible with magnification of 10x but remain clean to the naked eye.
Clarity VS2 Image Very Slightly Included 2: Diamonds of this clarity will have several groups of inclusion that are only visible with magnification of 10x. A small percentage of these are not eye clean.
Clarity SI1 Image Slightly Included 1: Only 50% of diamonds of this clarity have no visible inclusions so it is important your selected diamond is eye clean.
Slightly Included : 85% of diamonds of this clarity have some form of visible inclusion or blemish to the naked eye. Slightly Included : 85% of diamonds of this clarity have some form of visible inclusion or blemish to the naked eye.
Clarity I1 Image Included 1: Due to the high level of inclusions here, we do not recommended this clarity grade for diamond jewellery.
Expert tip 1
As magnification is needed to see impurities in diamonds witha VS1 grading or higher, a choice of VS1 or higher is a subjective quality choice which goes beyond what can be seen to the unaided eye. Larger Diamonds with these higher grades are much rarer and therefore command greater pricing premiums, and also tend to perform better as an investment.
Expert tip 2
Although SI1 and SI2 are in general not eye clean, the impurities may be light in colour or scattered and so in up to 20% of cases, SI1 graded diamonds may appear to be eye clean. That number falls to just 5% for SI2s.
There are many different types of impurities, but feathers and crystals are the most common forms of inclusions found in diamonds.
4. The Cut
Often confused with a diamond shape, the cut is actually the grading that determines how well the diamond sparkles. It encapsulates Brightness (white light reflecting from the top surface), Fire (flares of colour) and Scintillation (flashes of light).
The cut grading currently only applies to Round diamonds as they are technically easier to measure in terms of light performance. Other shapes – such as Princess cuts, Cushions cuts, Emerald shapes, do not have a cut grading on their certificate but 77 Diamonds provide an estimated cut grading based on equivalent parameters.
Cut grades range from Excellent, Very Good, Good, Fair and Poor. The grading takes into account various attributes of the diamond that cannot be seen or measured with the untrained eye. An excellent cut grading will have the best light performance, mainly influenced by the relationship of surface table and the depth of the diamond (not too deep or too shallow).
It is very hard to see the difference between an Excellent and a Very Good cut diamond as the direction of light is the same in both cut gradings. We therefore recommend you try to stick with an Excellent or Very Good cut, but if needed to fit the budget, a Good cut can offer an excellent-value alternative without any major compromises. Just make sure you are not on the "Deep" side or you will end up with a diamond that looks smaller than the actual carat weight.