From Rough to Exquisite: Basic Guide to Diamond Polish

As most of us know, diamonds in their rough form are far from magical. It takes a whole lot of patience, and a remarkable degree of skill, to turn a rough into the glittering, tempting and much more expensive polished diamond.

Polish is a term that refers to the degree of smoothness of every facet of a diamond. A good polish is essential for maximum light performance, thus allowing the diamond to glitter and shine. While a diamond’s polish features are located on the surface, flaws (inclusions) inside the diamond are checked against - and graded according - to the “clarity” category of the 4Cs.

How is a diamond polished?
After the diamond passes the test of a sorter, it is transferred to the expert hands of the diamond polisher. It is his or her task to ensure that the stone lives up to its full potential. The process of how diamonds are cut and then polished consists of five stages: planning, cleaving, bruting, polishing and inspecting.

We’ll skip directly to the polishing stage: once the shape of the rough is formed, the cutter places the rough on a rotating arm and uses a spinning wheel to polish it. The tools used in the workshop usually consist of diamond-bladed edges or discs lined in diamond dust (the only material hard enough to polish and cut diamonds is diamond), and they help the master polisher in creating the smooth and reflective facets on the diamond. 

How are polished diamonds graded?
The GIA uses a scale ranging from Poor to Excellent when grading polished diamonds. For diamonds with a polish grade of Excellent to Good, any polishing defects are not visible to the naked eye. In diamonds graded Fair or Poor, defects are noticeable at 10x magnification, and may be visible to the naked eye. Here is the full scale:

Excellent: No polish defects visible at 10x magnification.
Very Good: Any defects are extremely difficult to see at 10x magnification.
Good: Any defects are difficult to see at 10x magnification.
Fair: Defects are noticeable at 10x magnification, and may be visible to the naked eye.
Poor: Defects are visible to the naked eye.