Diamond Polish Grading

Diamond polishing is one of the factors that affect cut quality of diamond, other factors being cut proportions and symmetry of facets. So, it is important in understand about diamond polishing in order to understand cut quality of diamond.

Diamond Polishing is graded on the basis of:

  • Visibility of polishing lines on the surface of the diamond. Lesser are the polishing lines, it means superior is the polish grade.
  • Presence or absence of burnt facets.

Almost, all cut diamonds show polishing marks. But these lines are very fine and can be seen only by 10X or more magnification.

Polishing lines are formed during cutting process of diamond. These marks are the result of a diamond’s hardness being dependent on crystallographic directions. Hardness of each facet of diamond is different from other.

Since, cutter can set only one facet on the polishing wheel at a time, direction of polishing marks is same throughout a facet but their directions change with different facets.

Diamond Polishing
Diamond Polishing

Polishing lines can be seen when viewed from opposite side of the diamond. Polishing marks on the table of a diamond can be seen though the pavillion. If the relevant surface is slightly tilted and slowly moved under the light, the marks are visible in the reflected light. Polishing lines adversely affects the brilliance of diamond and reduces its transparency.

Polishing Lines on Table
Polishing Lines on Table

Diamond Polish Grades

Based on quality of polish, diamond is graded under following five categories:

  • Ideal/Excellent: Under this category, diamonds with hard to find polish line seen with great difficulty under 10X magnification are included.
  • Very Good: Under this category, diamonds with only faint polish lines that do attract attention under 10X magnifications are included.
  • Good: Under this category, diamonds with various small transparent polish lines visible through 10X magnifications are included.
  • Fair: Under this category diamond with obvious transparent or slight colored polish lines or burn marks visible through 10X magnification are included. Luster of diamond is affected when viewed through unaided eye.
  • Poor: Under this category, with prominent polish lines and marks are easily visible under 10X magnification. Luster of diamond is significantly reduced and it is noticeable with unaided eye.

Important considerations while choosing between different Polishing Grades

  • If you are considering buying diamond, always choose "good" polish grade diamond, if the diamond is of VS or SI clarity.
  • Diamonds with excellent and very good grades are expensive but there is no noticeable difference in luster of diamond as compared to diamond with "good" polish grade when seen through unaided eye.
  • Also, do note that if you are considering diamonds with Flawless clarity, choose "excellent" or "very good" polish grade. This is because, in flawless clarity even a very minute polish mark is easily visible due to high clarity. If you choose the "fair" or "poor" polish grade, brilliance of diamond will be noticeably reduced.

Return from Diamond Polish Grading to Cuts of Diamond page

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