BGM Diamonds: What Are They & How to Avoid

When it comes to choosing a diamond, whether for an engagement ring or other type of jewellery, the 4 Cs (carat, cut, clarity, and colour) are the industry standard for determining the quality.

However, there’s another set of factors affecting a diamond’s appearance that isn’t talked about as often — the BGM hues in a diamond. These subtle hues can be present in any diamond and are very difficult to detect by an untrained eye. 

If you’re set on finding the perfect diamond, it’s important for you to understand what BGM is in diamonds, how it can impact the appearance and value of the diamond, and how you can avoid a tinged diamond.

What does ‘BGM’ in diamonds mean?

BGM, in the context of diamonds, stands for ‘Brown, Green, or Milky’ — the type of background shade or hue that can be found in a stone. If you’ve done your research, you’ll know that diamonds come in many variations of colours in addition to the classic white, transparent appearance that they are most known for. 

Based on how the diamond was formed, it’s possible for it to feature some tinge of colour, most commonly in brown, green or milky hues. This is a problem for white diamonds, as the presence of even a little colour can have a big impact on the way that it reflects light, which ultimately affects its overall appearance (and value). 

Brown tinge in diamonds

A brown tinge is the most common occurrence for BGM hues in diamonds — the intensity of its hue is often celebrated for vivid colour diamonds. When it is present in a white diamond, however, it ends up producing a yellowish or tarnished appearance that makes the diamond less brilliant. 

Green tinge in diamonds

Diamonds with green tones are less common and can vary from pale to deep green. A greenish tint in a white diamond can indicate exposure to radiation, which may affect the diamond's perceived purity and lead to concerns about its origins and any treatments it may have undergone.

Milky appearance in diamonds

Microscopic inclusions within a diamond can cause a milky or hazy appearance due to the scattering of light within the stone. Instead of the usual brilliance and sparkle that is expected from a diamond, the milky hue diminishes the clarity of the diamond, making it less attractive. 

What causes BGM diamonds to have their appearance?

There are dozens of reasons why BGM hues appear in diamonds — most of which are outside of the control due to the way that diamonds form naturally in the earth. Some of the primary causes of BGM in diamonds include:

Trace elements

Trace elements within a diamond’s crystal structure can affect its colour. Nitrogen impurities, for example, may produce yellowish or brownish shades, while boron can give a bluish or greenish hue.

Lattice structure defects

The crystalline lattice in diamonds is made up of carbon atoms. Irregularities such as vacancies or displaced atoms can lead to colour changes, including brown and green. Additionally, exposure to radiation can also produce green tones.

Graining

The uneven light scattering caused by irregular growth patterns, known as graining, in a diamond's crystal structure can produce a milky or hazy appearance.

Inclusions

Inclusions are flaws found inside the diamond or just below its surface. They can consist of mineral deposits or clusters of tiny crystals, which can lead to a milky or cloudy appearance, diminishing the diamond's clarity and sparkle.

Why does BGM in diamonds matter?

The usual way to determine the quality of a diamond is by looking at its GIA certificate — diamonds that are graded by the Gemological Institute Of America (GIA) will be issued a certificate that outlines its official quality in terms of the 4 Cs. 

The challenge with BGM hues is that they aren’t measured or recorded by GIA certificates — meaning that the presence of brown, green, or milky hues can’t be detected just by looking at its GIA grading. For example, a diamond with a high clarity grade like VVS sounds stunning on paper, but if it ends up having a milky hue, it will not sparkle as expected.

How to avoid BGM when choosing a diamond

Obvious signs of BGM can often be seen by the naked or untrained eye (especially for milky hue diamonds), which makes it important for buyers to physically view and assess a diamond before making a purchase. 

Of course, not everyone knows what to look for when it comes to BGM in diamonds, which is why the best way to avoid BGM in a diamond is to have it inspected by a jeweller or diamond expert with an eye for detail. Experienced jewellers will be able to pick out even the most subtle signs of BGM hues and inform buyers of the potential impact it may have on the appearance and value of the diamond. 

At GS Diamonds, our entire collection of diamonds has been thoroughly assessed and handpicked by our team of jewellers using detailed reports from our network of diamond partners. Where possible, we provide 360-degree previews for our diamonds to help buyers identify BGM in diamonds before making a purchase, and screen all diamonds that arrive in our workshop to double-check for BGM. 

When you buy a diamond with us, we will search our diamond feed to filter out any diamonds with BGM so as to ensure that you get the best value for your money in terms of the quality of the diamond that you choose. We will also work with you to set your diamond in a piece of jewellery that brings out its best features, whether it’s an engagement ring or a necklace.