Diamond clarity

Natural diamonds form under extreme conditions, and many contain small features from that process, such as tiny crystals trapped inside. Clarity grades record those features. GIA calls the internal and surface-reaching ones inclusions and the external ones blemishes.

The scale has 11 grades in six categories, from Flawless to Included. A grader weighs five things about the features: their number, size, relief, nature and location. The final grade is set at 10x magnification with a loupe, a standard that AGS also calls an industry standard. Clarity is one of the 4Cs; for the features themselves, see diamond inclusions.

Eye-clean is a trade phrase for a diamond whose inclusions you cannot see with the naked eye. It is not an official GIA term or a grade on GIA's scale. AGS describes informal terms such as “eye clean” as vague, and says to have a diamond graded by a credentialed expert or a reputable laboratory.

The reason the phrase is slippery is that clarity grades are set under magnification, while you will look at the stone without it. Many blemishes and inclusions are not visible to the naked eye. A grade tells you how a skilled grader rated the stone at 10x. Whether you can see anything in a ring on your hand depends on where the features sit, how large they are, and how much light the stone returns.

That is why two stones with the same grade can look different. Location and relief sit on GIA's list of factors beside the number and size of the marks.

Most diamonds in jewellery shops fall between VS and SI. It describes the inclusions in VS stones as minor and those in SI stones as noticeable. The higher grades, FL, IF and the VVS pair, are rarer, and diamonds with higher clarity are rarer in nature, which is reflected in price.

One way to begin is to look at VS stones and then at SI stones in person. It is a starting point, not a rule, because you can only judge the individual stone. If a stone in a lower grade looks clean to you from the distance at which the ring will be seen, you do not need to pay for a higher grade. If you see a mark, move on.

The I grades sit apart. On the GIA scale their inclusions are obvious under 10x magnification and can affect transparency, brilliance and durability, so treat them with caution and look closely at any stone in this range.

Shape changes how much clarity shows, so the same grade is not equally safe in every cut. Brilliant cuts can hide small flaws among their many facets. Step cuts such as the emerald cut have larger facets that show clarity more readily, so a buyer who wants an eye-clean step cut may need a higher clarity grade.

In practice that means a brilliant shape such as a round brilliant or oval can often look clean at a lower grade, while an emerald or Asscher cut asks for a higher one. The exact grade is the stone's own, so check the report and then look at the diamond.

Not by itself. Clarity affects value because rarer grades cost more, but the beauty of a diamond depends more on cut. GIA's view is that a well-cut diamond can look brilliant even with a lower colour or clarity grade. On the GIA scale, VVS inclusions are difficult for a skilled grader to see even at 10x, so a step from VS2 up to VVS2 buys rarity more than a visible change.

If you are designing a custom engagement ring, the design studio lets you note the shape and stone you prefer, so the clarity conversation starts from the diamond you want. Browse engagement rings to see how setting and shape play together.