Think of a piece of wood and the grain that runs through it. It can be coarse or fine, it can be barely noticeable or it can obvious, and it can even have different colors. Diamonds can have graining as well. It is a result of discontinuities in the carbon lattice at the atomic level. Sometimes graining is of a nature that can be visible and impact the clarity grade. Or it can be transparent and have no impact on the clarity grade whatsoever. Here are some things to understand about diamond graining.
Types and Impacts of Graining
There are several types of graining including colored graining (brown, green, white), reflective graining, surface graining, and transparent internal graining. Colored and reflective graining can have negative visual impacts on the diamond and may be factored into the clarity grade. When internal graining affects the clarity grade, a comment will appear on the report. Surface graining can be confused with polish lines, and when present, will be noted on comments. Since each facet is polished individually, in one direction, a polish line will stop at the junction. Surface graining will cross over more than one facet or change direction within the same facet on the diamond. Transparent graining is not counted against the clarity grade.(*see video of transparent graining below)
Highly Magnified Image of Colored Graining (courtesy of GIA)
Highly Magnified Image of Reflective Graining (courtesy of GIA)
When you look at a diamond under magnification, or an enlarged image or video of a diamond with transparent graining, certain angles may show the grain lines. Potentially you could have some mirror reflections of the same grain, some showing it and others not, depending on their differing angles. You could also have facet reflections showing grain lines alongside contiguous facet reflections that do not show them, which could give the incorrect impression that the lines stopped at the facet junction. Ultimately these calls are made by trained graders doing careful physical inspection at 10X.
Graining and Clarity Grades
Whether graining will be considered a clarity factor will depend on the type of graining, its visibility, and whether it impacts the overall transparency of the diamond. As an extreme example, white graining can be so evenly distributed in a diamond that it results in an overall haze or cloudiness. This can drop the overall clarity grade as far as Si with no other features or inclusions present. An explanatory comment would be included on the report such as “Clarity grade based on graining”.
Reflective and colored graining are both considered clarity features, with the clarity grade impacted proportional to the amount and visibility of such graining.
Surface graining can look like incomplete polishing – a failure of the facet to attain a mirror finish. If severe enough, this can impact the luster and overall crispness of the diamond and will result in a clarity downgrade.
Transparent graining may exist in the diamond without affecting transparency or impacting the clarity grade. It will typically not be mentioned on the report.
GIA Reporting on Graining over the Years
Reporting on graining at GIA has changed and evolved over the decades. Originally, graining was not considered a clarity characteristic and was not part of a diamond report. It was sometimes noted in the grader’s file for in-house identification purposes. Later, whitish graining that would affect transparency would be noted under comments. Today, whitish, colored or reflective graining is factored into the clarity grade and is mentioned in comments. Transparent graining, when deemed significant, is mentioned in comments but is not factored into the clarity grade.
Conclusion
Like other characteristics detailed on a laboratory report, graining is largely an identification factor, part of the unique ‘fingerprint’ of the diamond. In some cases, such as colored or reflective graining, it does impact the visual properties of the diamond and becomes a factor in the clarity grade. It will influence the grade proportional to its visibility and/or impact on light performance. Transparent graining is usually of negligible consequence and may not even be visible under magnification from most angles. In such cases (which are relatively common), transparent graining may be technically observable under magnification, even when not mentioned on the laboratory report.