What Are SI Diamonds?

Clarity may be one of the more confusing of the diamond 4Cs. There’s a lot to consider and clarity grades that are higher may not technically get you a better diamond. Among savvy diamond buyers, the SI clarity grade is one of the more popular choices, but is it always going to be the best option? Let’s see how SI clarity stands up and when buying an SI clarity diamond is a good idea.

What Are SI Diamonds?

SI stands for Slightly Included. This term is a measure of a diamond’s clarity, which establishes the visual appearance of a diamond and its internal inclusions or external blemishes. To obtain a grading of SI, the diamond would have noticeable inclusions that can be easily seen under 10x magnification. These inclusions may be visible to the naked eye as well, without any magnification.

On the diamond clarity scale, SI grades are closer to the bottom with only I (Included) grades lower. The SI range is broken down into two grades: SI1 and SI2. The difference between these two is in the amount, size, and how noticeable the inclusions are when viewed, with SI1 being the better grade.

SI diamonds commonly show various sized versions of inclusions such as needles, knots, indented naturals, clouds, and crystals, and tiny surface-reaching inclusions like chips, cavities, or feathers. But it’s important to remember that when evaluating a diamond, the clarity grade tells you the size and harshness of an inclusion in relation to the makeup of that particular diamond – it does not indicate whether you can notice any of this with the naked eye.

A SI clarity oval diamond

The Difference Between SI1 and SI2

Five clarity quality factors make up a diamond’s clarity assessment: size, number, location, relief, and nature of the inclusions. Then the diamonds are assigned one of 11 clarity grades on these factors. For SI diamonds, both SI1 and SI2 diamonds will have inclusions that you might be able to notice with the naked eye.

For clarity grades that are so close together, it may not seem like there will be much of a difference between them. However, when comparing the two gradings, there are some definite distinctions you can make:

  • - SI1 diamonds tend to have fewer inclusions overall than SI2 diamonds.
  • - SI1 diamonds usually cost more (when all else is equal).
  • - SI1 and SI2 diamonds will have the same types of inclusions, but they will be larger and more numerous in SI2 diamonds.
  • - SI2 diamonds may appear to have a slightly foggy appearance when compared to an SI1 diamond.
  • - Both SI1 and SI2 diamonds could potentially be eye-clean.

As with any diamond, the price of an SI diamond will depend on the cut quality, color, shape, and carat weight. So, if all things are relatively equal between two diamonds, but one is SI1 clarity and the other is SI2 clarity, the SI1 diamond will likely average about 10% more in cost than an SI2 diamond.

si1 diamond with inclusions

Example of a typical SI1 clarity diamond, where there are minor inclusions throughout (circled in red)

si1 diamond - side small inclusion

Here’s an example of the type of SI1 clarity diamonds that we look for, where the inclusion is small, off to the side, and invisible to the naked eye without magnification. The trade informally calls this SI1+ clarity:


si2 clarity diamond

Compare the above examples to the following SI2 clarity diamond, where the inclusions are more severe and most likely visible to the naked eye.

Comparing SI with VS Diamonds

If you move one clarity step above an SI diamond, you will find a VS diamond. The VS stands for Very Slightly Included, meaning they contain minor inclusions that range from difficult to somewhat easy to see under 10x magnification. While VS diamonds can have many different types of inclusions, they must be very tiny relative to the size of the diamond for a VS grading to be given.

The category of VS diamonds also has two gradings, VS1 and VS2, with the general distinction being that VS1 inclusions are difficult to see while VS2 inclusions are somewhat easy to see. So why are we bringing up VS clarity diamonds? Well, because many people tend to get scared off of SI diamonds thinking that visible inclusions must be bad, and they opt for a VS diamond instead.

While every diamond choice is up to personal preference, buying a VS diamond over an SI diamond when all else is close to equal is going to cost about 10-20% more. That’s a big price jump when, if you do some work, you can very likely find an eye-clean or close to eye-clean SI diamond and either save money or put that 10-20% savings into other features or the setting of your dreams.

Your perfect diamond is always going to be the result of finding a balance between all of the diamond quality characteristics. So while clarity is important and gives you an inclination to the amount of sparkle and light reflection you’ll get, the best clarity grade is always going to be the one that works well with the cut, shape, and color to produce an overall beautiful diamond.

vs2 clarity diamond

Here is a typical VS2 clarity diamond, where there is hardly any blemish even at 10x magnification

vs1 clarity diamond

Here is a VS1 diamond, which for nearly everyone would appear Flawless  

Tips For Buying SI Diamonds

SI diamonds have grown in popularity as educated buyers are more aware of the quality and value that this clarity grading holds. Although they may have clarity characteristics that are visible to the naked eye, they are unlikely to detract from the sparkle. Also, when the diamond is set and worn, anyone viewing the diamond will usually not be close enough to discern any imperfections.

When buying an SI diamond, understanding more about specific clarity features will help determine how the diamond will look and whether it’s susceptible to chipping or breaking. Most imperfections in SI diamonds tend to be inclusions, cloudy formations, pinpricks, feathers, and twinning wisps. Each of these can be large or small, and occur in any color with white or black being the most likely. To start, the placement is important. Imperfections near the surface or visible through the center table are to be avoided. When they are near the edges of the crown, they’re less noticeable and can even be hidden by prongs, in some cases.

To help in the process of evaluating placement, size, and depth of inclusions, a diamond’s certificate should have a clarity plot. Labs like GIA always include the clarity plot for diamonds 1 carat or larger, which is basically a diagram of the diamond with markings for where every visible imperfection resides. If an inclusion looks questionable, it will be worth it to consult with a trusted jeweler to get an experienced opinion.

When it comes to diamond durability, the most dangerous imperfections are the large ones. These interrupt the diamond’s crystal structure, which keeps the diamond in one piece. So these make the diamond particularly vulnerable to breaks, especially if they are close to or at the surface. This is important if you’re considering diamond shapes with weak points, like pear, marquise, or princess cuts.  

A good SI1+ diamond can be a good way to get the best combination of value and size. Your best bets are going to be with brilliant cuts such as round, oval, cushion, radiant, marquise, princess and pear shape diamonds – these cuts hide inclusions better than shapes such as emerald and asscher. Keep in mind though, that the larger the diamond, the more likely you’ll easily see inclusions. As for step cut diamonds like the Asscher cut, emerald cut, and baguette cut, an SI diamond is not the way to go since the faceting style easily shows imperfections. In this instance, it would be important to buy a VS1 clarity diamond or better.

An SI diamond is often considered to be a hidden gem of great value when all the clarity features line up for a beautiful diamond. It may require extra diligence to find an eye-clean SI diamond in the shape and carat weight you want, but the value is really unbeatable, both now and long-term.

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