SI1 and SI2 are two adjacent diamond clarity grades that are often compared. But what is the exact meaning behind these letters, and how should you decide between the two grades when shopping for diamonds?
SI1 and SI2 Diamond Clarity on the Grading Scale
On the grading scale used by the G.I.A. (Gemological Institute of America), diamond clarity grades are denoted by letters. SI clarity is the fifth best grade on this scale.
The four higher grades are (in descending order): FL (Flawless), IF (Internally Flawless), VVS (Very, Very Slightly Included) and VS (Very Slightly Included). There is only one grade after SI: I, standing for Included.
The SI clarity grade is split further into two sub-grades: SI1 and SI2, with SI1 indicating higher clarity.
SI1 and SI2 Clarity Grades Defined
SI1 clarity diamonds have inclusions that are easily visible under 10x magnification. In rare cases, there might be inclusions visible with the naked eye, but these flaws will usually be few and barely noticeable.
Click here to see a selection of SI1-clarity diamonds and take notice of where their inclusions are located as well as how big they are.
SI2 clarity diamonds have inclusions that are easy to see under a 10x loupe, and some of these flaws are likely to be visible with the naked eye.
Now click here to see a selection of SI2-clartity diamonds and look closely to see how they differ from SI1-clarity stones in terms of the size and position of their inclusions.
Difference Between SI1 and SI2 Clarity
The main difference between SI1 and SI2 clarity lies in the visibility of inclusions: They are more easily noticeable in SI2 stones than in ones graded SI1.
The reason for this difference is that SI2 inclusions are, on average, bigger and more numerous than those in SI1 stones.
It is clear that SI2 diamonds’ inclusions are more visible under magnification, but what about inclusions that are visible to the naked eye?
The answer is that SI2 stones are more likely to have such flaws. However, their visibility will depend on where they are located and what color they are.
Visible inclusions in SI2 diamonds are more likely to be found towards the periphery of the stone, and in many cases, the diamond may look clean when looked at from the top.
From the side, however, you will be more likely to see inclusions without a loupe.
We recommend that you buy diamonds online from places where you can see the stones from all sides to examine them for visible flaws.
Choosing Between SI1 and SI2 Clarity
The choice between SI1 and SI2 clarity comes down to the tradeoff between price and quality: All else being equal, SI2 diamonds are cheaper, but SI1 stones are cleaner, on average.
However, not all diamonds within a certain grade are created equal. Some SI1 stones may have inclusions visible with the naked eye, and there will be SI2 diamonds that look reasonably clean.
Each diamond is different and unique. This is why you should use clarity grades only as a guideline and look at a number stones to pick out the ones that look good to you.
As a rule of thumb, try to find a stone that is eye clean, i.e., one that has no inclusions visible under normal viewing conditions.
SI2 diamonds may be more likely to have visible inclusions, but these flaws are also more likely to be visible from the side, not so much from the top.
And you may be able to find an SI2 stone whose inclusions are inconspicuous simply because of their color and location.
Also, if your diamond can be mounted so that the setting will hide the inclusions, then you can save some money by buying an SI2 stone that will look reasonably clean when worn. Check out a selection of different diamond ring settings here.