Diamond Inclusions and Blemishes: Understanding the Differences

Posted in: Diamonds | Posted on: Tue, 19 Sep 2023

When it comes to buying a diamond, it's important to understand the difference between inclusions and blemishes.

While both of these terms refer to imperfections in a diamond, understanding the difference between inclusions and blemishes can help you make an informed decision when shopping for a diamond, and ensure that you get the best value for your money.

Diamond inclusions refer to internal defects or impurities that are present within the diamond from when it was formed. These inclusions can be naturally occurring minerals, such as crystals or pinpoints, or can be caused by structural defects within the diamond itself. Inclusions can affect the clarity and overall beauty of the diamond, and can also potentially affect its value. 

The effect of inclusions on the appearance and clarity grade of a diamond depends on how visible the inclusions are, how many there are, and their location. A black included crystal directly under the diamond’s table, for example, will have a greater impact on a diamond’s appearance, clarity grade, and value than a similar-sized white included crystal that is under one of the star facets and does not reflect throughout the diamond.

Blemishes, on the other hand, refer to external marks or imperfections that are present on the surface of the diamond, e.g., a nick, knot, scratch, abrasion, minor crack or cavity or poor polish. Also a natural on the girdle or an extra facet is usually considered a blemish. Blemishes can also affect the clarity and overall appearance of the diamond but can have a lesser impact on its value than inclusions since some blemishes can potentially be polished away to improve the cut grade of the diamond (at the cost of a loss in diamond weight).

Inclusions and blemishes are typically evaluated and graded by a professional Gemologist using a 10x magnification loupe. The Gemological Institute of America (GIA) uses a grading system to determine the clarity of a diamond, taking into account both inclusions and blemishes. The clarity grades range from "Included" (I3) to "Flawless" (FL). 

The most popular diamond grade in the New Zealand market has historically been “Slightly Included 2” - SI2. There can be a wide range of diamonds even within the SI2 grade, however, with “high” SI2s and “low” SI2s. Our diamond experts can assist you in finding a good value diamond within a particular clarity grade. 

A grade of Internally Flawless means there are no inclusions under 10x magnification but may have minor blemishes, while a grade of Flawless means there are no visible blemishes or inclusions under 10x.

Understanding the difference between inclusions and blemishes is important. While both can affect the overall appearance of the diamond, it's important to understand that not all inclusions and blemishes are visible and some can even have next to no impact on the diamond's appearance. Consider both the clarity grade and the overall appearance of the diamond to ensure that you get the best value for your money.

For more details on clarity grades, see our clarity grade guide.