For diamond certification the Cut grade is generally only provided for Round diamonds. This is because it is extremely difficult to assess the ideal proportions of the likes of princess, emerald and Cushion cut diamonds.
However, there are some experts that have done research about the ideal proportions for these shapes, and thus we will provide you with a small guide below.
ROUND BRILLIANT CUT
This is the most brilliant of all the diamond cuts. Here is a guide to the depth percentage and table percentage you should be looking for in regards to each of the sought after grades.
ROUND BRILLIANT CUT
Excellent
Depth percentage – 60 – 63
Table percentage – 53 – 58
Very good
Depth percentage – 58 – 64
Table percentage – 52 – 62
Good
Depth percentage – 56 – 67
Table percentage – 50 – 67
STEP CUTS
(Asscher and Emerald)
ASSCHER
Excellent
Depth percentage – 58 – 65
Table percentage – 60 – 65
Very good
Depth percentage – 55 – 70
Table percentage – 59 – 70
Good
Depth percentage – 52 – 75
Table percentage – 52 – 75
EMERALD
Excellent
Depth percentage – 58 – 65
Table percentage – 60 – 65
Very good
Depth percentage – 55 – 70
Table percentage – 59 – 70
Good
Depth percentage – 52 – 75
Table percentage – 56 – 75
MODIFIED BRILLIANT CUTS
(Pear, Princess, Marquise, Radiant, Oval, and Heart)
Here is a guide to the depth percentage and table percentage you should be looking for in regards to each of the sought after grades.
PEAR
Excellent
Depth percentage – 58 – 64
Table percentage 55 – 62
Very good
Depth percentage – 57 – 66
Table percentage – 53 – 64
Good
Depth percentage – 56 – 68
Table percentage – 52 – 65
PRINCESS
Excellent
Depth percentage – 62 – 73
Table percentage – 57 – 72
Very good
Depth percentage – 60 – 77
Table percentage – 55 – 75
Good
Depth percentage – 57 – 83
Table percentage – 52 – 85
MARQUISE
Excellent
Depth percentage – 58 – 64
Table percentage – 55 – 62
Very good
Depth percentage – 57 – 66
Table percentage – 53 – 64
Good
Depth percentage – 56 – 68
Table percentage – 52 – 65
RADIANT
Excellent
Depth percentage – 62 – 68
Table percentage – 58 – 65
Very good
Depth percentage – 58 – 70
Table percentage – 56 – 70
Good
Depth percentage – 57 – 75
Table percentage – 54 -75
OVAL
Excellent
Depth percentage – 58 – 64
Table percentage – 55 – 62
Very good
Depth percentage – 57 – 66
Table percentage – 53 – 64
Good
Depth percentage – 56 – 68
Table percentage – 52 – 65
HEART
Excellent
Depth percentage – 52 – 60
Table percentage – 55 – 62
Very good
Depth percentage – 50 – 62
Table percentage – 50 – 62
Good
Depth percentage – 45 – 65
Table percentage – 52 – 65
MIXED CUTS
(Cushion)
Here is a guide to the depth percentage and table percentage you should be looking for in regards to each of the sought after grades.
CUSHION
Excellent
Depth percentage – 62 – 68
Table percentage – 58 – 65
Very good
Depth percentage – 58 – 70
Table percentage – 56 – 70
Good
Depth percentage – 57 – 75
Table percentage – 54 – 75
Online vendors list their diamonds for sale, the stones are actually filtered and organized based on the individual vendor’s own set of standards.
For example, one vendor might assign an Excellent cut grade to a princess diamond with 71% depth and 67% table while another vendor might assign a Very Good cut grade to the same diamond.
Next, the numbers and proportion charts found in our article are just guidelines we think nice looking fancies might fall in.
There are really no hard and fast rules when it comes to selecting fancies. The charts are there merely to act as guidelines to help you out.
We can’t place a figure to correlate a fancy’s visual beauty based on the table and depth proportions only.
Besides that, the polish and symmetry grading of a fancy is really unrelated to how the diamond will look in real life.
Very often, you will find that a Very Good/Good diamond can look a lot better than another diamond with Excellent/Excellent polish and symmetry.
Origins of Fancy Shaped / Cut Diamonds
When cutting rough diamonds it is more desirable and profitable to make a round stone, as opposed to a fancy shaped one. Rounds diamonds are easier to cut since all the facets in a tier are cut to the same angle and depth. If this is done correctly then the diamond should be ideal in terms of brilliance and dispersion. To best achieve this they are usually cut on automated machines.
However, with oddly shaped rough material this is not always possible, due to the nature of its shape. In this case it is more sensible to obtain maximum yield from the rough and rather to cut a fancy shaped stone more similar to the shape of the rough. For example, if the rough is a rectangular shape it would be best to cut an emerald, radiant or baguette shaped diamond, the obvious advantage being to greatly reduce the weight loss of the finished diamond. Cutting a round diamond would be wasteful.
Fancy shapes must nearly always be cut by hand because they have to be customised and optimised from irregular shaped rough material. This can happen if the lapidary or cutter needs to cut an inclusion out of a regular octahedron, in which case an odd shape is left. Generally, though, fancy shapes are more common in larger sizes because of the cost and time involved in cutting.
Proportioning
Fancy cuts also require a variety of angles to get the facets to come together. (If you cut eight symmetrically arranged facets at the same angle, they will come to a point and give you an octagonal outline.
In order for the facets to reach the ends of an emerald or other shape, the angles and/or facet arrangement has to change.) As a result of the varying angles, fancies are not as brilliant as rounds.
Fancy cut diamonds have a much broader range of proportions. Length to width ratios are not standardized.
For example, emerald and princess cuts often have tables to 80%, and marquis’ diamonds are so thin that they are significantly less brilliant than other shapes.
Fancies cannot be judged by the same standards as rounds. Colour and clarity grading the same, but proportion and cut grading varies considerably.
Proportion ranges are much greater for fancies than with rounds.
There is no general agreement as to what proportions are best, (as between long or fat pears, stubby or elongated emerald cuts.)
Shape appeal counts highly in the proportion grade, but it is difficult to evaluate as there are no standards to go by.
It requires a judgment based on your knowledge of diamonds in general and the particular shape you are working with.
Begin your shape analysis by asking three critical questions;
- Are corresponding parts evenly made?
- How does the chosen cut affect brilliance and dispersion?
- Do the chosen proportions add weight that does not contribute to the diamond’s beauty?
Major Symmetry
- Should be symmetrical, top to bottom and side to side.
- Hold with tweezers on table and culet. Look at sides and ends. (Hearts and pears only ends.)
- Any variations will affect brilliance, plus visual appeal.
- As with rounds, Major Symmetry (proportions,) or Minor Symmetry, (finish.)
- Off center table. If obvious with loupe, major.
- Table and girdle not parallel. Should be straight, not wavy. Hearts and pears will be slightly larger at ends. If obvious under 10x, major.
- Culet or keel off center. Should be cantered and straight. From side, (emerald, oval, marquis,) ends should taper down at same angle. If one end is steeper than the other, it qualifies as off center.
- If noticeable under 10x, major.
- Hearts and pears, culet should be centered on widest part of gem. Too high or too low, when viewed face up is considered off center. Judge without magnification. If it detracts from appearance, it is major.
- Sides not parallel on step cuts. If noticeable without magnification, it is major.
- Uneven corners on step cuts. Should be equal length. If you can see variation without magnification, it is major.
- Uneven wings on hearts, pears, and marquis. If you can see variation without magnification, it is major.
- Uneven lobes on hearts. If you can see variation without magnification, it is major.
- Uneven shoulders on ovals and pears. If you can see variation without magnification, it is major.
- Uneven bulge on pavilion of step cuts. Even if not eye visible, major.
