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Diamond Symmetry - Everything You Need To Know

A diamond's symmetry is the arrangement, size, and shaping of diamond's facets. The facets are the flat planes that run along the surfaces of the diamond. Symmetry is angles and lines that form the placement of the facets. Nowadays, symmetry is completely controlled by the manufacturing process. Machines very carefully cut diamonds to produce the most accurate shapes. However, at times the diamond cutter will leave a symmetry imperfection in the diamond in order to prevent a different inclusion from showing in the finished diamond. Symmetry is a subset of the diamond's cut grade.

Symmetry grades refer to how carefully and cleanly diamond facets have been cut in relation to each other. Low symmetry grades can have a negative effect on a diamond's sparkle and its ability to hide inclusions. While symmetry is not as crucial of an element in a diamond as the cut is, it can still make a different in the visual appearance of the diamond. However, it is important to avoid diamonds that have poor symmetry as this can be detrimental to the look of the diamond. Although symmetry is not as big of decider in the visual appearance, it can make a price different of up to 15% between the various cut grades. Therefore, it can be a good charecteristic to look at when comparing two diamonds that otherwise have the same cut grade and similiar charecteristics. Symmetry typically ranges from 'excellent' to 'poor'.

Diamond Symmetry Chart

Each Reputable jewellers's diamond certificate displays the symmetry grade, using the following scale:


Symmetry Symmetry Description
Excellent No symmetry defects visible under 10x magnification
Very Good Any defects are very difficult to see under 10x magnification
Good Any defects are difficult to see under 10x magnification
Fair Defects are noticeable at 10x magnification, and may be visible to the unaided eye
Poor Defects are visible to the unaided eye

Diamond symmetry chart.

Diamond Symmetry Chart Description

Excellent - The diamond's facets are perfectly sized and proportioned. The location of the diamond's attributes, such as culet, girdle table, etc. are in all the perfect locations. The diamond is not out of shape. The diamond can achieve an Excellent cut grade.

Very Good - The diamond's facet sizes and proportionately are near perfect. There may be one or two disproportionate elements that are viewed under 10px magnification. The impact on the diamond Cut grade and sparkle are minimal. The diamond can still achieve an Excellent cut grade.

Good - The size or location of attributes and facets is slightly disproportionate. The sparkle of the diamond is affected, as a result. The diamond can achieve a Very Good cut grade, at best.

Fair & Poor - The facets and proportionately are noticeably imperfect. In non-round shapes, the shaping is not perfect. The diamond's sparkle and brilliance are impacted adversely and the diamond can achieve, at best, a Good cut grade. A diamond with poor symmetry may misdirect light that travels into the diamond, sending it off at slightly wrong angles, and thereby reducing the diamond's brilliance.

Examples of symmetry imperfections: off center culet, misshapen facets, off center table, faceting that is not properly pointed, crown and pavilion misalignment, table and girdle not parallel. More information on symmetry defects is listed below. The symmetry grade is based on the severity of these infractions.

The grading methodology for symmetry can be further sub-divided into 2 types of categories - proportions and facets related.

A symmetry alteration that affects the alignment and balance of a diamond's facet structure is considered a proportioning flaw. These flaws are usually measurable and affect the diamond's overall appearance. These include the following:

On the other hand, facet related flaws are focused on the regularity of individual facets. Basically, similar facets should all be cut to equal sizes and regularity (i.e. all bezel facets should look the same, all pavilion main facets should look the same, etc.):

Types Of Symmetry Defects - Proportion Related Symmetry Features



Out-of-Round

Out of Round

Deviation from the circular shape of a round diamond; a flattened area such as that created by a natural or extra facet also constitutes out-of-round. Comparison of the minimum and maximum diameters can help assess roundness. The round cut diamond is not well shaped and the ratio of length to width is greater than 1.10.


Table off-Center

Table off Center

Deviation of the table from the central position on the crown; results in opposing bezels of differing sizes. When viewed through the table, more of the pavilion is seen to one side of the culet than the other. The table facet at the top of the diamond is not perfectly center. The light performance of the diamond may be affected. An off-center table may be listed as "Table Off-Center" (T/oc) on a diamond's report.


Culet off-Center

Culet off Center

Deviation of the culet from the central position on the pavilion; results in the cross-line formed by lower half facet junctions to be bowed or bent. When viewed through the table, more of the pavilion is seen to one side of the culet than the other. The point at the bottom of the diamond is not directly centered. Light performance may be reduced in the diamond pavilion. If the culet deviates from the center position, gemologists will mark it as "Culet Off-Center" (C/oc).


Table & Culet Alignment

Table Culet Alignment

Displacement of the table facet and culet in opposite directions. The proportional locations of the tablet and culet are incorrect.


Table & Girdle Not Parallel

Table And Girdle Not Parallel

The girdle plane is not parallel to the table. If the table and girdle are not parallel but the girdle is straight, the table may be the problem. The table may be off-center or tilted, which creates any uneven crown height. Gemologists may refer to this as a "Crown Height Variation" (CHV).


Wavy Girdle

Wavy Girdle

Undulating girdle. The girdle isn't in the straight line around the diamond. This can affect the evenness of a diamond's setting. A diamond's girdle should be parallel to the edges of its table, creating a straight, precise line.


Girdle Thickness Variation

Girdle Thickness Variation

Variation of the girdle thickness at "valley" positions. Additionally, an imperfect girdle may be thicker in some spots than others, which can cause issues with light dispersion. "Girdle Thickness Variation" (GTV) would be noted on a diamond's report.


Crown Angle Variation

Crown Angle Variation

All eight crown angles are not equal; typically related to table off-center.


Pavilion Angle Variation

Pavilion Angle Variation

All eight pavilion angles are not equal; typically related to culet off-center.


Note: That variations in crown height and/or pavilion depth result from one or more of the following deviations: wavy girdle, table and girdle not parallel, crown angle variation, pavilion angle variation and/or girdle thickness variation.



Types Of Symmetry Defects - Facet Related Symmetry Features



Misalignment

Misalignment

Displacement of the crown and pavilion facets in relation to each other. A gemologist may note this imperfect as a "Misalignment" (Aln) on a report.


Non-Pointing

Non-Pointing

Fully formed facet that does not reach its prescribed location (short facet) or is incompletely finished (open facet), resulting in adjoining facets not meeting at precise points. If a facet is not pointed, it interrupts the basic design of the diamond, which was engineered to shine as much as possible. For instance, a round brilliant diamond has 58 perfectly pointed facets aligned precisely for the ultimate sparkle.

A diamond may have a "Short Main" (SM) or "Short Bezel" (SB) if the point does not reach its intended location. But, it may also have an "Open Main" (OM) or "Open Bezel (OB) if the point is unfinished altogether. Or, if the pavilion has uneven points, it may be noted as a "Lower Half Variation" (LHV) in the report.


Misshapen Facet

Misshapen Facet

Difference in shape or size between one facet and another of the same type; or distortion of a given facet. A proper diamond table should be octagonal, with 8 equally shaped sides that abut equally shaped facets. If the facets are not all the same size or shape or the table has uneven sides, it can alter the face-up appearance of the stone.

Misshapen facets that affect a diamond's face-up appeal include bezels (MB) and stars (MS). If the star facets vary in length, it may be noted as a Star Percentage Variation (SPV). Or, the table may not be octagonal (T/oct or TEV).


Non-Octagonal Table

Non-Octagonal Table

The table is not a regular octagon; results in misshapen star and bezel facets. A proper diamond table should be octagonal, with 8 equally shaped sides that abut equally shaped facets. If the facets are not all the same size or shape or the table has uneven sides, it can alter the face-up appearance of the stone.

Misshapen facets that affect a diamond's face-up appeal include bezels (MB) and stars (MS). If the star facets vary in length, it may be noted as a Star Percentage Variation (SPV). Or, the table may not be octagonal (T/oct or TEV).


Missing Facet

Missing Facet

Asymmetrically missing or deleted facet. You may notice an "Extra Facet" (EF) , see below, in your report, or maybe a facet is actually missing altogether! In this case, you may see "Missing Facet" (MF).


Natural

Natural

Part of the original rough diamond's surface that remains on the polished diamond; typically causes an out-of-round girdle outline, short facets or misshapen facets. Naturals are rough spots on a diamond from before the stone was polished. Usually, they start at the girdle and move either upward to the crown or downward into the pavilion. If a diamond has rough patches, a gemologist will note it has "Natural" (N) sections.


Extra Facet

Extra Facet

Additional facet placed without regard for symmetry and not part of the standard cutting style; typically causes an out-of-round outline, short facets or misshapen facets. Sometimes, a gem cutter may add extra facets to a diamond, throwing off its sparkle. Although they can appear anywhere, extra facets typically manifest near the girdle on the pavilion.

You may notice an "Extra Facet" (EF) in your report, or maybe a facet is actually missing altogether! In this case, you may see "Missing Facet" (MF).



Diamond Symmetry Scales Examples

Select Symmetry Scale

Excellent Very Good Good Fair poor


Excellent

Excellent

Misalignment ranges from no symmetry features to minute symmetry features that can be viewed with difficulty face-up at 10X magnification.

Some typical features that would establish an excellent category include misaligned, misshapen, non-pointed, or extra facets that are barely visible.


Note: Some features were enlarged for the purpose of illustration; it is the appearance at 10X magnification that is considered during evaluation. Note, too, that each finish category encompasses a range of appearances and the selected examples do not represent the highest or lowest point of that category.

Very Good

Very Good

Minor symmetry features are seen face-up at 10X magnification.

Some typical features that would establish a very good category include slight table or culet off-center, a slightly out-of-round outline, and/or minor misshapen, non-pointed or extra facets.


Note: Some features were enlarged for the purpose of illustration; it is the appearance at 10X magnification that is considered during evaluation. Note, too, that each finish category encompasses a range of appearances and the selected examples do not represent the highest or lowest point of that category.

Good

Good

Noticeable symmetry features are seen face-up at 10X magnification. The diamond' s overall appearance may be affected when viewed with the unaided eye.

Typical features that would establish a good category include any proportion feature that is noticeable - such as table or culet off-center, out-of-round outline, wavy girdle, table and girdle not parallel, girdle thickness variation or crown or pavilion angle variation - and/or many noticeable misshapen, misaligned, non-pointed or extra facets.


Note: Some features were enlarged for the purpose of illustration; it is the appearance at 10X magnification that is considered during evaluation. Note, too, that each finish category encompasses a range of appearances and the selected examples do not represent the highest or lowest point of that category.

Fair

Fair

Obvious symmetry features are seen face-up at 10X magnification. The diamond's overall appearance is often affected when viewed with the unaided eye.

Typical features that would establish a fair category include any proportion feature that is obvious - such as table or culet off-center, out-of-round outline, wavy girdle, girdle thickness variation, crown or pavilion angle variation - many obvious misshapen or extra facets, misalignment or non- pointing on most of the facets and/or an obvious missing facet such as a bezel or main.


Note: Some features were enlarged for the purpose of illustration; it is the appearance at 10X magnification that is considered during evaluation. Note, too, that each finish category encompasses a range of appearances and the selected examples do not represent the highest or lowest point of that category.

Poor

Poor

Prominent symmetry features are seen face-up at 10X magnification. The diamond's overall appearance is significantly affected when viewed with the unaided eye.

Typical features that would establish a poor category include any proportion feature that is prominent - such as table or culet off-center, out-of-round outline, wavy girdle, girdle thickness variation, crown or pavilion angle variation - or prominent faceting distortion.


Note: Some features were enlarged for the purpose of illustration; it is the appearance at 10X magnification that is considered during evaluation. Note, too, that each finish category encompasses a range of appearances and the selected examples do not represent the highest or lowest point of that category.



Symmetry has a limited impact on the appearance of a diamond and a greater impact on price. A diamond with 'excellent' symmetry and polish may be priced higher than a diamond with 'good', 'fair' or 'poor,' because they are perceived as more valuable. A diamond with a lower symmetry grade will also have a higher probability of noticeable defects.

For diamonds with a symmetry grade of excellent to good, symmetry should not be used as a primary factor in choosing a diamond, since each of these grades is possible in diamonds of exceptional appearance.

A diamond with poor symmetry may misdirect light that travels into the diamond, sending it off at slightly wrong angles, and thereby reducing the diamond's brilliance. Because diamonds with poor symmetry have defects visible to the naked eye, these diamonds should be avoided in all cases.

Symmetry is more important in diamonds of VVS2 Clarity and higher, since the very subtle defects produced by Fair or Poor symmetry (which can resemble pinpoint inclusions) would compromise the diamond's otherwise flawless appearance.

As mentioned, despite its modest impact on appearance, symmetry has a significant impact on price; a diamond with excellent symmetry and polish may be priced 10%-15% higher than a diamond with good symmetry and polish. This premium has more to do with consumer's perceived value of "excellent" grades, than the actual effect on a diamond's appearance.

There's a big misconception that the presence of symmetry defects indicate poor cutting skills. That is not true.

In fact, most of the decisions made during the cutting process are carefully planned and "real" mistakes are extremely rare. You see, the main goal a cutter wants to achieve when polishing a rough diamond is to get the maximum value out of the rough.

Often times, the decision to polish a rough stone prioritizes carat weight retention and compromises cut quality. Cutters may purposely create facets that don't meet accurately in order to attain 'magic weights' like 1.00 carat or to eliminate inclusions from the end product.

The rationale behind doing this is that a diamond with "good" symmetry (at 1 carat weight) is more marketable and valuable compared to a diamond with "excellent" symmetry (at 0.96 carat weight). It's sad that cut quality is usually the first aspect to get sacrificed but this is how economics work in real life.

Sometimes, an extra facet or a misshapen facet is purposely introduced to remove an inclusion and to improve the diamond's clarity grade. This is a calculated move as the symmetry flaw doesn't impact value as much as the improvement in clarity grade does.

Final Thoughts

A diamond should not be chosen or rejected based solely on symmetry. Because the overall cut grade already incorporates symmetry, it should be used as the primary determinant when choosing a diamond. When comparing two diamonds of equal cut grade, symmetry (and polish) can then be used as a further refinement or tie breaker.