Indicating Factors of Assigning a Clarity Grade (6.47)
Most people might assume that clarity grading is strictly based on the amount of inclusions in a diamond. The amount of inclusions is very important but other factors can easily shift a grade one or two notches.
The location of the inclusion(s) is critical. A dark crystal which lies right next to the girdle may be graded SI1 but the exact same crystal dead center may shift it to SI2. A white crystal in the table may be assigned SI1 but the exact same crystal placed deep in the pavilion may cause severe reflections, shifting it to SI2.
The color of an inclusion has a direct effect on its visibilty, so this will easily influence the clarity grade. A brown feather could be assigned a lower clarity than a white feather. A dark crystal could be graded lower than a white crystal. It is the contrast of the inclusion that will affect the grade the most, when color tone is involved.
Transparency of an inclusion could be considered part of the contrast factor, but nonetheless it is very important in judging the clarity grade. One cloud may be very dense and easily seen, whereas another cloud of the same size may be very faint and difficult to detect due to its transparency. Some feathers, although primarily white, have a tendency to be somewhat transparent, making them less visible and more appealing in a stone’s overall beauty.
The size of the diamond must be considered in your final clarity grade assessment. The same size inclusion in a quarter carat versus a ten carat is obviously going to lead to different clarity grades, as a consequence of different proportional relationships. Usually an SI2 will be 100% eye-clean, but sometimes due to the nature of the stone, that won’t always be the case. A five-carat emerald-cut that has a small white inclusion in the table, may have a GIA report with a clarity grade of SI1, but the inclusion may still be visible to the naked eye. Dark crystals are much easier to spot with the naked eye, but the stone may still fall into the SI range.
The lack of brilliance and dispersion in a stone may make an inclusion more visible, whereas the same inclusion in an ideal cut may well be concealed to the naked eye. The idea is not to over-emphasize eye visibilty in a diamond. Perhaps your vision is better than 20/20, or your perception may be more critical than for other graders.
Durability is also a factor that can make a difference of a grade in clarity. If a feather is open to the surface and has partially fallen out, this will be a good reason to grade the stone as Imperfect. If the same feather is deep within the stone and poses no threat to durability, it might easily be grtaded in the SI category.