Diamond Polish and Symmetry Explained

Most people know about the four Cs. Polish and symmetry are two more grades on a diamond report that quietly affect how a stone looks. They are part of what the cut grade summarises.

What is polish?

Polish describes the quality of a diamond's surface finish. During cutting, the facets are polished smooth. Imperfections such as tiny scratches, polishing lines or a "burn" mark left by heat can remain. The grade describes how visible those are at 10x magnification.

What is symmetry?

Symmetry describes how exactly the stone's shape and facets match their intended design. It looks at things such as whether the table is centred, whether facets line up and whether the outline is even.

How they are graded

Both are graded on the same scale as cut: Excellent, Very Good, Good, Fair and Poor. A stone with Excellent polish and symmetry has very few imperfections at 10x magnification.

Do they change how a diamond looks?

At the top grades, the effect is invisible. At lower grades, poor polish can make a surface look slightly dull, and poor symmetry can cause light to scatter unevenly. For a stone of any size, the difference between Excellent and Very Good is not something you would notice, but a Fair or Poor grade could affect the look.

Where they sit in the cut grade

For round brilliant diamonds, the laboratory's cut grade takes account of proportions, polish and symmetry. See diamond cut grades explained. Because polish and symmetry are part of that, a stone with Excellent cut generally has high marks on both.

Reading them on the report

Look for the entries labelled Polish and Symmetry, usually near the cut grade. You will see them in how to read a diamond certificate step by step.

What to aim for

• For a significant solitaire: Very Good or Excellent on both.
• For small stones in jewellery: individual grades are not issued, but the overall standard of the workmanship is what matters.

Do they affect price?

Yes. Stones with Excellent polish and symmetry are priced above those with lower grades, other things being equal. For a buyer on a budget, Very Good in both is often almost indistinguishable to the eye.

A caution about "triple Excellent"

You may hear sellers describe a stone as "triple Excellent", meaning Excellent cut, polish and symmetry. It is a worthwhile standard for a solitaire. It does not tell you about colour, clarity or fluorescence, so check the whole report.

What damage looks like

Polish can wear if a diamond is struck by another diamond. Store pieces separately to avoid this. See how to store diamond and gold jewellery.

Polish and symmetry in small stones

In jewellery with many small diamonds, no one grades each stone's polish and symmetry. Instead, the quality shows in the finished piece: a bright, even sparkle and neat, regular facets when you look through a loupe. Cheaply cut small stones are often visibly uneven, with a dull or glassy look. This is one reason to look at a piece under good light and, if you can, under magnification before you buy.

Common questions

Can polish be improved later? Yes, to a degree. A cutter can repolish a facet, though this takes a tiny amount of weight.

Which matters more, polish or symmetry? Both are small details compared with cut proportions. Aim for Very Good or better in each.

Judging with your eyes

Use a loupe with your jeweller and look at the facet edges. Crisp edges and clean surfaces are signs of good finish. Book an appointment to see the difference, or begin with our diamond rings.