SI1 and SI2 (slightly included)

How to read it

SI1 and SI2 sit below VS on the GIA clarity scale and above the included grades. GIA’s graders find SI inclusions easy (SI1) or very easy (SI2) to see face-up at 10× magnification, and GIA says they usually can’t be seen with the unaided eye. GIA says most diamonds seen in jewelry stores fall between VS and SI.

Also searched as: SI, SI1, SI2, SI clarity.

What decides SI1 or SI2

GIA’s graders weigh five things: how big the inclusions are, how many, where they sit, their relief (how much they contrast with the diamond) and their nature. An inclusion off to the side of a stone affects the grade less than the same inclusion directly under the table. The cut changes how easily inclusions are seen: GIA says they are easier to see in an emerald cut, with its long rectangular facets, than in a round brilliant.

SI3, “eye clean” and other laboratories

Some grading laboratories issue an SI3 grade. GIA does not: it says it has studied the idea at various times and sees no reason to change its scale. “Eye clean”, a trade term for a diamond whose inclusions can’t be seen with the naked eye, is not a GIA term either. HRD Antwerp’s scale keeps SI1 and SI2 and calls them “small inclusions”.

The plotting diagram

A GIA grading report maps the inclusions and blemishes on a drawing of the stone seen from the crown and from the pavilion, with symbols for their type and relative size, listed in order of their importance to the grade. No two diamonds below Flawless and Internally Flawless have the same combination, so the diagram also identifies the stone.