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), 10points = 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 |
|
|
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. |
