Diamond Symmetry

Everything You Need to Know About Diamond Symmetry

A well aligned round brilliant compared against one with poor facet symmetry — The same shape and the same facets, one aligned and one not

Quick Summary

Symmetry is how precisely a diamond's facets line up with each other. It is graded separately from cut, on a scale from Excellent to Poor, and it is the difference between a stone that looks crisp and one that looks slightly wrong without you being able to say why. On round brilliants it is a fine adjustment. On pointed and elongated shapes it is the single most important thing to check, because a point that sits even slightly off centre makes the whole ring look crooked on the finger.

People mix up symmetry, polish and cut constantly, so it is worth separating them.

Cut is about proportions: are the angles right for light to come back. Symmetry is about alignment: are the facets where they should be, matched across the stone. Polish is about surface: how cleanly each facet was finished. All three appear separately on an IGI report, and all three affect sparkle. Read diamond anatomy first if the facet names are unfamiliar.

What Graders Actually Check

Table off centre. The flat top sitting slightly to one side rather than centred on the girdle.
Culet off centre. The bottom point not sitting directly below the middle of the table.
Out of round. A round brilliant that is very slightly oval.
Table not parallel to girdle. The top plane tilted relative to the widest point, so the stone leans.
Misshapen facets. Facets of different sizes where they should be identical, or facets that do not meet cleanly at a point.
Extra or missing facets. Usually added to remove a surface flaw during cutting.
Wavy girdle. The girdle rising and falling round the stone rather than sitting level.

Grades run Excellent, Very Good, Good, Fair and Poor. Good is where careful buyers start to look twice, and anything below that is visible to the naked eye.

Why It Matters More on Some Shapes

A round brilliant is symmetrical in every direction, so small errors have nowhere obvious to show. Fancy shapes are a different matter, and they carry no overall cut grade at all, which makes symmetry the main quality signal you have.

Heart. The most demanding shape of all. The two lobes must match exactly, the cleft must be centred and sharp, and the point must sit on the same axis. Everyone already knows what a heart should look like, so an uneven one is obvious even to someone who knows nothing about diamonds.
Pear. Draw a line from the point through the middle of the rounded end; both halves must mirror exactly. Off by a fraction and the stone looks tilted no matter how it is set.
Marquise and Dutch marquise. Two points that must sit on the same axis, and two wings that must match in curve. The Dutch version is less forgiving still, because its straighter wings give an error nowhere to hide.
Oval. Watch for uneven shoulders and for one end fuller than the other.
Emerald and Asscher. Step cuts show everything. Corners must be cropped equally and the terraces must run parallel, or the hall of mirrors effect breaks up.
Princess. Four corners that must match, and a table square to them.
Cushion and elongated cushion. Corners should be equally rounded. One tighter corner makes the stone read as lopsided.

How Much Symmetry Matters, Shape by Shape

Fancy shapes carry no overall cut grade, so symmetry is the main quality signal you have. This is where to look on each one.

How Much Symmetry Matters, Shape by Shape
Shape	Risk	What must match	What goes wrong
Heart	Highest	Two matching lobes, a centred sharp cleft, the point on axis	An uneven lobe looks wrong even to someone who knows nothing about diamonds
Pear	Very high	Both halves mirrored across the long axis	The stone looks tilted however it is set
Marquise	Very high	Both points on one axis, wings matching in curve	One wing fuller than the other
Dutch marquise	Very high	The same, but with straighter wings	Straight wings give an error nowhere to hide
Oval	High	Even shoulders, both ends equally full	One end fuller, or shoulders that do not match
Emerald	High	Corners cropped equally, terraces parallel	The hall of mirrors effect breaks up
Asscher	High	A truly square outline with a centred table	The stacked reflections stop lining up
Princess	Moderate	Four matching corners, table square to them	One corner tighter than the other three
Cushion	Moderate	Corners equally rounded	The stone reads lopsided without an obvious cause
Round	Lowest	Centred table, centred culet, a true circle	Errors have nowhere obvious to show

The pattern is simple: the more the eye already knows what the shape should look like, the less forgiving it is. A heart is unforgiving because everyone can draw one. A round is forgiving because an error has nowhere to show. Compare all twelve in diamond shapes.

How to Check Symmetry Yourself

Look straight down at the table. Not at an angle. The table should sit centred inside the outline with an even margin all the way round.
Find the axis. On any pointed or elongated shape, imagine the long centre line. Both halves should be identical reflections.
Check where facets meet. Facet junctions should form clean points. Small flat spots or T junctions where three facets meet unevenly are a symmetry fault.
Turn it over. Look at the pavilion from below. The culet should sit dead centre and the main facets should be equal.
Look at the girdle edge on. It should run level round the stone, not wave up and down.
Read the report. Symmetry and polish are listed separately from cut. Ask for the IGI report before you buy, not after.

Marquise three stone lab grown diamond ring where both points sit on the same axis — On a navette centre, both points must sit on one straight axis

Dutch marquise three stone lab grown diamond engagement ring in yellow gold front view — On a navette centre, both points must sit on one straight axis

Does Symmetry Change the Price?

Yes, but less than most people assume, and less than cut or carat weight. Dropping down the symmetry scale saves a modest amount, and the further you drop the more visible it becomes, which is a poor trade on a ring worn every day.

The more useful way to think about it: symmetry is cheap to get right and impossible to fix afterwards. A stone cannot be recut to correct it without losing weight. It is the wrong place to economise, and Ronora does not.

Symmetry and Setting

A setting cannot rescue poor symmetry, but it can expose it. A bare prong solitaire shows the outline completely, so any asymmetry is on display. A bezel traces the outline in metal, which draws the eye straight to an uneven edge. A halo is the most forgiving, because the ring of small stones breaks up the silhouette.

This is why we check symmetry before a stone is ever set, rather than hoping the setting will disguise it.

Checked Before It Reaches You

Every Ronora diamond is Excellent cut, and symmetry is checked on every fancy shape before it goes into a setting, because fancy shapes carry no overall cut grade to rely on. Diamonds of one carat or more ship with their own IGI report, where symmetry and polish are listed separately so you can see the grades yourself. Next, see what symmetry produces in the sparkle guide, or how the facets are arranged in diamond anatomy.