What the grades mean
| Grade | Definition | Eye clean? | Rough price |
|---|---|---|---|
| VS2 | Inclusions minor, findable at 10x with effort | Yes, by definition | Baseline |
| SI1 | Inclusions noticeable at 10x | Usually, depends on placement | 15 to 25 percent less |
The grading standard judges everything at ten power magnification. VS2 sits far enough up the scale that nothing reaches the naked eye. SI1 is the first grade where that stops being automatic, which is exactly why the price drops.
Placement decides everything at SI1
Two SI1 stones can be completely different purchases. The grade tells you roughly how much is in there. It does not tell you where.
An inclusion directly beneath the table, in the middle of the stone, is in the most visible position possible and a dark crystal there can be spotted by a sharp eye. The same inclusion out near the girdle disappears under a prong and nobody will ever know it exists.
The plotted diagram on the certificate maps this. Read it before you decide anything.
The one SI1 trap
Watch for the word cloud on the certificate, especially if the comments section mentions that clarity is based on clouds not shown. A dense cloud spread through the stone does not look like a spot, it makes the whole diamond slightly milky, and it will dull the brilliance in a way a single crystal never would.
That is the one SI1 to walk away from. Everything else in the grade is usually fine.
What to do with the money you save
Put it into cut. Going from Very Good to Excellent changes how the stone behaves in every room you walk into, where the clarity difference between SI1 and VS2 changes nothing you can see.
If cut is already Excellent, the next best use is carat, or simply keeping the money.
Not sure what you are looking at?
Photograph the stone and the app gives you a visual read on the 4Cs, an estimated value range, and what to check next. Free on iOS and Android.
Frequently asked questions
Is SI1 eye clean?
How much cheaper is SI1?
How do I check an SI1 before buying?
Does clarity affect sparkle?
Worth being clear: everything here, and the app itself, is an educational reference. At-home tests narrow things down, they do not certify a stone. Before you buy, sell or insure anything of real value, get it looked at by a certified gemologist or an independent appraiser.