Diamond Education

Welcome to Diamond School. The information contained is based on the 4C’s. Diamond School contains more integrated information and goes beyond the 4C’s.

Disclaimer: Information contained in Diamond School is accurate, based on many years of experience. It is to help people understand diamonds up to an intermediate level. We are obligated from this information only to our customers.

Shape

There are several different Shapes of diamonds, the most popular is the Round Brilliant Cut. Round Brilliant Cut diamonds are designed to be the brightest, the most modern having 57 – 58 facets:
Shape
Other popular traditional Shapes are:
Shapes

Weight and Cut

Weight of diamonds and other gems is measured in CARATS. One carat = 100 points = 0.2 grams. eg: 50 points = 0.50 Carat (half carat), 10 points = 0.10 Carat, 1 point = 0.01 Carat, etc. The size : weight ratio of Fancy Cut diamonds varies more than properly Cut Round diamonds. See comparison of sizes below for Round Brilliant Cut diamonds.

2.00cts. 1.75cts. 1.50cts. 1.25cts. 1.00cts. 0.75cts. 0.50cts. 0.25cts. 0.10cts. 0.05cts.
8.0mm 7.8mm 7.4mm 7.0mm 6.5mm 5.9mm 5.2mm 4.2mm 3.0mm 2.4mm


The diameters shown above are indicative only and will fluctuate. The diameter measurements when viewed on all proper certificates will very rarely be measured as perfectly round, for example 5.2mm may read: 5.15 - 5.22mm x depth.

Very precise measuring instruments are used to measure diamonds and any slight difference shown on certificate is normal, however a big difference for example: 5.10 - 5.30 x depth is usually not normal for a Very-Good Cut and definitely unacceptable for an Excellent Cut (visually, a Very-Good or Excellent Cut Round Brilliant will appear perfectly round).

H & A ( Hearts & Arrows ) is a characteristic that is confirmed on some Very-Good and Excellent Cut diamonds. When diamond is viewed from the crown 8 perfect arrows are visible and when viewed from the pavilion 8 perfect hearts are visible. For the diamond to qualify for this additional grading a strict criteria applies. If the hearts and arrows don’t appear as a perfect 8 of each then H & A is not granted.



The Cut grade is sub-divided into two main categories:

1: Proportions (Prop.)
2: Symmetry (Sym.)

Polish is a third sub category, which is sometimes integrated with the symmetry.

The cut grade can be determined from a combination of Proportion and Symmetry / Polish. This method is one way to determine a Cut grade and we believe it’s also the best method.
Some certificates do not use the word “Proportion” but instead use the word “Cut” which is also correct (as Cut can mean Proportion), however Proportion is more specific and in our opinion it’s a better word to use. The diamond certificate is mainly to protect the end consumer (as they usually haven’t got the knowledge of an expert) so the perfect certificate should include separate grading of: Proportion, Symmetry, Polish and an overall summary that combines the values of the 3 categories and summarises them to 1 overall value to determine a “Cut Grade”. As a reputable diamond dealer myself that is what I have been doing for years.
Why I am making this point: If you described your cockatoo as a parrot you are correct as it is a parrot, but it can be misleading as people perceive a parrot as a colourful smaller bird and not a big plain white bird. The word “Cut” is said generally in the industry, like saying the word “Parrot”. Some dealers use it to describe Proportion only and others, like myself use it to describe the overall combination of Proportion, Symmetry and Polish.

Excellent Cut Very Good Cut Good Cut Fair Cut Poor Cut
P S P S P S P S P S P S P S P S P S P S P S P S
Exc/Exc Exc/VG VG/VG VG/G *G/VG G/G G/F F/G F/F F/P P/F P/P
*G/VG is borderline between Good and VeryGood. It can be recognised as Good or VeryGood Cut

Round Brilliant-Cut diamonds:
Proportions are more important than Symmetry and Symmetry is more important than the Polish.

Fancy cut diamonds:
Proportions and Symmetry are similarly important but Polish is less important.

Round brilliant cut diamonds:
Cut grading as on most world recognised diamond grading certificates. Table below indicates the difference in the Cuts. Excellent is the best Cut, however Excellent makes usually have a smaller table diameter, some people prefer a bigger table and go for a Very-Good Cut. Excellent Cut grade is usually not used for the proportion (AKA: Cut) of Fancy Shapes diamonds.

Proportions:

  Excellent Very good Good Fair Poor
Crown angle
(degrees)
33-35 32-36 30-38 26-44 25-45
Pavilion depth 42-44% 42-45% 41-47%    
Table diameter 53-58% 52-63% 50-67% 49-72% 48-73%
Total depth 59.2-62.4% 58-63.8% 56.8-65.9% 54-70.1% 53.9-70.2%
Girdle thickness 0.51-2.95% thin-sl.thick 1% deduction 0-2.95% ex.thin-sl.thick 2% deduction 0-5.7% ex.thin-v.thick 4% deduction 7 and 8% deductions  
Culet None-medium None-medium None-sl.large    

Clarity

1: Good - Excellent proportion. More light and more brilliant on top.
2: Fair - Poor proportion (deep). Light escapes through sides.
3: Fair - poor proportion (shallow). Light escapes through bottom.


Symmetry - finish grade

Grade Definition
Excellent none or very negligible Symmetry deviations and/or finish faults
VeryGood none or negligible Symmetry deviations and/or finish faults
Good finish deviations are hardly perceptible
Fair/Medium the Symmetry deviations are perceptible
Poor the Symmetry deviations are significant

A minimum Cut grade of Good is required to maintain a nice cut with high brilliance. The Cut is very important since it makes the diamond sparkle the way it should, the diamond's beauty comes from it's sparkle. The better the Cut grade and usually the better the sparkle. Weight, Colour and Shape are a preference but Cut and Clarity represent quality. For example: If a diamond was graded: 1.00 ct F SI1 with a VeryGood Cut grade it will look better to the naked eye than a 1.00 ct D VVS1 with a Fair Cut grade, or 1.00ct F SI1 Excellent Cut grade will look better to the naked eye than a 1.00ct D VVS1 with a Good Cut grade. In these cases Cut prevails over Colour and Clarity.

Clarity has a role in the brilliance of the diamond only when there is so much inclusions in the stone affecting brilliance, Clarity grade: I 2 and lower.

Round Brilliant-Cut diamonds should have 57 - 58 facets. Grading of facets is Symmetry. Sometimes a diamond will have 1 or a few extra facets which will be indicated (ef) in green marking on the certificate. Green is always for external features. Extra facets are OK if underneath crown, on pavillion or girdle. If on top then it will down grade Symmetry more than if underneath. One or a few extra facets is usually better than 1 or a few less facets.

Example:
Some diamonds we have seen had VeryGood Proportions and Symmetry, 1 extra facet was underneath and the Cut grade was still VG/VG, if there wasn't any extra facets then it would have still been the same. It was difficult to find the extra facet even with 10x magnification and not noticeable from top of diamond. When the Cut grade is high then these features will be minor and are nothing to worry about. In severe cases or when there is irregular shaped facet(s) then Symmetry is downgraded.


Colour and Fluorescence

Colour

Diamonds come in a range of Colours, from totally Colourless to tinted. The most rare and valuable Colour is the highest and whitest, Colour D. Colour however is a personal choice, a lower Colour that isn't as valuable is still just as good in quality as a higher Colour if the Clarity and Cut is the same. Some natural Fancy Coloured diamonds, eg: Intense yellow, pink, blue, red, etc can be much more valuable than the whitest diamonds. Natural Fancy Colours are not classed as low Colours. The lowest Colour is a personal choice. The lowest Colour to stay true white is Colour H. Colour I is a commercial white, Colour J is slightly tinted but can still look white or whitish. I and J Colours may still be OK for white diamond shoppers. People who demand the finer whites should start looking from Colour G and above.

D - F G H I J K L
M N O P Q R S

Fluorescence

Diamonds can have nil, slight, medium, strong or very strong Fluorescence.

Fluorescence when strong and very strong can make Colour of diamond appear different under certain types of lighting. Some people like this but most prefer nil and no higher than medium. Blue Fluorescence will make Colour look whiter, especially if it's a low Colour. A yellow Fluorescence will make Colour look lower, especially if it's a high Colour.

Do not take Fluorescence into account if graded nil, slight and in most cases medium. Negligible Fluorescence usually cannot be seen with eye and is nothing to worry about. Fluorescence is not necessarily bad. In some cases it can be advantage, eg: Budget restricts that you buy a low Colour diamond, but you prefer a higher Colour. Strong – very strong blue Fluorescence will make diamond appear whiter, but beware sometimes it can also make diamond look milky – so you should see the diamond first or buy from a reputable source that will advise you correctly.

Clarity

Most diamonds contain inclusions that may be visible with naked eye or only visible under 10x magnification. SI2 and higher is not visible with naked eye under normal grading rules. SI3 is a split, a diamond that was too good to be a I1 and not good enough to be a true SI2, however usually SI3 stones are graded either SI2 or I1 as most laboratories do not grade SI3.

The lowest Clarity we recommend is I1. (I2, I3 heavy inclusions) (I 4, I 5 - reject stones).

The highest Clarity is FL: Flawless, IF: Internally flawless with minor surface blemishes. (Other term used by some labs, LC: Loupe clean, meaning: Flawless or Internally Flawless)

VVS VVS1, VVS2: very, very small inclusions, very difficult to see under 10x magnification.
VS VS1, VS2: very small inclusions, difficult to see under 10x magnification.
SI SI1, SI2: small inclusions, easily seen under 10 x magnification, not visible through the crown with naked eye.
I1 (also known as P1): inclusions can be seen easily under 10x magnification, but do not influence the brilliance. Inclusions are visible with naked eye through crown.
I2 also known as P2): large and/or numerous inclusions, which can be seen through the crown with naked eye and are damaging to brilliance.
I3 (also known as P3): larger and/or more numerous inclusions which are easily visible with naked eye and are very damaging to brilliance.

There are other features in some diamond that have a role in the Clarity, good examples are cloud or graining in the diamond. Example: D IF with a faint cloud was downgraded to D VS2. As long as the Clarity is downgraded by the grading laboratory to VS2 then it's OK since it's sale value was a D VS2 which is much less valuable than a D IF.

Diamond grading certificates will indicate all internal features (inclusions, etc) with red markings and all external features with green markings. External features are usually not part of Clarity grading.

FL      IF VVS1   VVS2 VS1    VS2 SI    SI I1 I2 I3

Note: VVS1 is slightly higher clarity than VVS2, 1 is always higher than 2 in each clarity grade.
I = Imperfect P = Pique (*both terms are used but have the same meaning).


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