The SI3 designation exists, and is most often used to disguise the fact that a stone is of the lowest quality. The GIA (Gemological Institute of America) does not recognize this classification, and so would classify such a stone as I (included). The GIA has six broad classifications. They are F (Flawless), IF (Internally Flawless), VVS (Very very slightly included), VS (Very slightly included), SI (Slightly included), and I (Included). Most of these categories include small gradations.
Included simply means the stone has noticeable flaws which can be seen with the naked eye.
Why Would a Jeweler Say a Diamond is SI3?
SI3 sounds better than I, doesn’t it? That’s the obvious answer to this question, and an SI diamond would command a higher price than a diamond classified as I. However, in some methods of classification other than the GIA, the designation does actually exist, so it can’t completely be a scam.
To further complicate matters, the EGL (European Gemological Laboratory) does have an SI3 grade. So, your gem may have been graded by the EGL. The differences from one grade to another are so minute that anyone other than a trained gemologist would have trouble distinguishing one from the other.
Therefore, you see, we must rely on the best authorities for our information. In the United States, that is the GIA. There are many smaller laboratories, in fact, that have different variations on these themes, and they all issue certificates.
Whose Certificate is Most Valid?
When you see the certificate which comes with a diamond you are inspecting, the most reliable information comes from the GIA. If you are looking at a certificate from a smaller laboratory, you should be aware that its authenticity may be questioned. There are other valid labs, such as AGS (American Gemological Society) and IGI (International Gemological Institute). The most preferred is still the GIA, so when you are shopping, ask to see the certificate from the GIA. If one doesn’t exist, note that, and decide to pay a lower price for that piece of jewelry, because its quality can’t be authenticated.
Buying a diamond can be very tricky, as we have shown. However, one way to be sure you are getting the quality of diamond you are paying for, is to buy a loose diamond. Not only can you choose the mounting you prefer, but more importantly you will be able to inspect the stone from every angle. If it is SI and not I, you will see no, or fewer imperfections when examining it. Mountings can cover up inclusions. Therefore, this method will allow you to pay the correct price for the diamond you choose.
Now, when you go to the jewelry store on a shopping trip, you will be better informed and receive the best value for your money, no matter what grade diamond you decide to purchase.