Diamond Clarity Grades & the Inclusions Behind Them
Under 10x magnification, a purplish red speck inside a natural diamond can be pyrope garnet, a crystal of another mineral enclosed deep in the earth’s mantle as the diamond formed. Olivine and diopside turn up as inclusions too, and so do crystals of diamond. Crystallographic studies published since 2017 suggest many garnet and olivine inclusions formed before the diamond that now surrounds them. A GIA grading report records the garnet as a crystal, one of the symbols on its plotted diagram, marked where the grader saw it and drawn at its approximate size.
The Clarity Scale in Brief
A clarity grade describes how easily a skilled grader can see a diamond’s inclusions and blemishes face-up at 10x magnification. GIA’s scale dates to the 1950s and has 11 grades in six categories.
- Flawless. An FL stone shows no inclusions and no blemishes at 10x.
- Internally Flawless. In an IF stone, the only features visible at 10x are blemishes.
- Very, Very Slightly Included. VVS1 and VVS2 inclusions are minute and range from extremely difficult to very difficult to see.
- Very Slightly Included. VS1 and VS2 inclusions are minor and range from difficult to somewhat easy to see.
- Slightly Included. SI1 and SI2 inclusions are noticeable, easy to very easy to see.
- Included. At I1, I2, and I3, the inclusions are obvious and can affect transparency and brilliance.
GOODSTONE’s diamond search covers Flawless to SI2.
Inclusions in Natural Diamonds
The crystals trapped as a diamond grows range from single specks to dense groups. A pinpoint is a crystal small enough to show as a dot at 10x. Grouped so tightly that the individual points are hard to tell apart, pinpoints form a cloud with a hazy look. Where the diamond’s crystal structure changed orientation partway through growth, pinpoints, clouds, or crystals can gather along that plane as a twinning wisp, a feature GIA considers unique to natural diamonds. Needles are thin, elongated crystals that look like tiny rods at 10x.
Feathers came later. A feather is a break in the diamond, often white and feathery in appearance, and it can record a rough trip from the mantle to the surface. Graining, lines of misaligned carbon atoms, usually comes from the crystal deforming after it formed, though irregular growth can produce it too. A black speck ringed by a flat fracture is typically a sulfide crystal. The fracture around it is lined with graphite and can open as the inclusion expands while an eruption carries the diamond up from the mantle.
Cutting exposes a few more. Polishing can bring a diamond crystal to the surface, where it becomes a knot. When a surface-reaching crystal drops out or is forced out during polishing, it leaves an angular opening called a cavity, and a cavity also forms when part of a feather breaks away. Sometimes a patch of the rough’s original surface survives as well, dipping below the polished facets as an indented natural.
Inclusions in Lab-Grown Diamonds
Without a history in the mantle, a lab-grown diamond has no garnet or olivine crystals and no twinning wisps. What it does contain depends on how it was grown. HPHT growth dissolves carbon in molten metal such as iron and nickel, and bits of that metal can end up inside the crystal as flux inclusions. They look black in transmitted light and metallic in reflected light. Some are thin rods and others irregular pieces. Enough of them can make a stone respond to a magnet. Published testing found that reaction consistently only in SI and I stones, so a stone with no magnetic response can still be HPHT grown.
CVD diamonds grow on a seed plate from hydrogen and a carbon-containing gas such as methane. They contain no metal. When a CVD stone has inclusions, they are most often dark specks of non-diamond carbon. Graders describe them with the terms used for natural diamonds.
Lab-grown stones examined by GIA have skewed toward the higher grades. In reviews published in 2016 and 2017, most CVD stones GIA had examined graded VVS2 or VS1, and most HPHT stones VS1 or VS2. Near-colorless natural diamonds in that comparison centered on VS2 and SI1. Those figures are about a decade old, and GIA expected lab-grown clarity to keep improving.
How an Inclusion Sets the Grade
A diamond with several inclusions receives one clarity grade, set by the feature with the greatest effect. Graders call it the grade setter. In a stone with a large feather and a few scattered pinpoints, the feather sets the grade. A diamond with many tiny inclusions can still grade high. A grader may also look at higher power under a microscope, but the final grade is always judged at 10x with a loupe.
GIA weighs each feature by its size, number, position, nature, and relief. The factor that matters most changes from stone to stone. Larger and more numerous features lower the grade more. Reflections of an inclusion in the facets count toward the number. An inclusion off to the side has less effect than one the same size directly under the table. Relief measures contrast, so a dark sulfide crystal is easier to see than a colorless crystal of the same size. Nature covers what a feature is and how it affects the diamond. A feather can be the grade setter in a VVS1 stone only if it is small and on the pavilion, with little or no depth.
Clarity or Color First
Color and clarity grades are determined differently. A color grade describes the body color of the whole stone, judged table-down against masterstones of known grade. A clarity grade is judged face-up at 10x and often rests on a single feature, the grade setter, whose position the report’s plot records. With other factors equal, a step up either scale raises the price per carat. In a trade between the two, a lower color grade adds body color to the whole diamond. A lower clarity grade allows a grade setter that is larger or easier to see, and the plot shows if it lies under the table or out near the girdle.
Durability & Surface-Reaching Inclusions
Diamond resists scratches better than any other natural material, but it is only somewhat tough, the term for resistance to chipping and breaking. Its atoms are bonded less tightly along four cleavage directions, and a cutter can split rough by striking it sharply along one of them. A hard enough blow can split a finished stone too, during setting or in wear.
Diamonds with serious durability problems generally do not survive cutting, so the risk in a finished stone comes from particular inclusions and where they are. A feather or other inclusion that reaches the surface near the girdle or a point can start a chip if the stone is struck there. An open cavity at the girdle is damaged about as easily as a chip. Depth counts too. A feather that runs from crown to pavilion, or about a third of the way or more into the stone, can be a durability concern. Sudden, extreme temperature changes can make existing fractures spread.
GIA lowers a clarity grade for this kind of risk only rarely, usually within the I grades. A VS or SI grade says little about it. A feather near the girdle can be checked on the report’s plot and under a loupe before the stone is set.
Blemishes & the Flawless Grade
Blemishes are confined to the surface. A GIA plot draws them in green or black, where inclusions are red. Several come from cutting. Polishing can leave polish lines, fine parallel grooves that stop at the facet edges, or a hazy burn mark where it generated too much heat. An extra facet, one the cutting style does not call for, is most often placed near the girdle. A natural is a different kind of leftover, a patch of the rough’s original surface, usually on or near the girdle. Wear accounts for others, though only another diamond can scratch a diamond.
Repolishing can remove many blemishes, so they rarely affect a grade below IF. The line between Flawless and Internally Flawless is drawn by blemishes alone.
Clarity Enhancement
Laser drilling treats a dark inclusion by boring a tiny channel from the surface to it. The laser either vaporizes the inclusion or opens a path for a strong acid to bleach it. Internal laser drilling reaches a dark inclusion another way, by opening a feather around it until the feather breaks the surface, and the result can look like a feather that formed naturally. Because laser drilling is permanent, GIA grades drilled diamonds and marks the drill holes on the plot. The report’s comments also name the treatment. A laser inscription on the girdle, such as a report number, uses a laser too but does not count as a clarity characteristic.
Fracture filling works on feathers that reach the surface. A glass-like material containing lead fills the break, and the fracture remains, only harder to see. The filling is not permanent. Common repairs can damage it, as can cleaning with steam, acid, or ultrasonic solutions. A filler that turns dark cannot be made colorless again. GIA does not grade fracture-filled diamonds, including drilled stones with filled holes.
In the U.S., the Federal Trade Commission’s Jewelry Guides call for a seller to disclose a gemstone treatment that is not permanent, creates special care requirements, or materially affects value. Fracture filling meets the first two. For a stone sold online, the disclosure belongs in the product description. Every GIA diamond grading report lists any treatment GIA has found, so a GIA report with no treatment noted means GIA found neither drilling nor filling when it examined the stone.