- Canary diamonds – a common term used to describe a yellow diamond.
However, it is not a technical term that you will see on a GIA (or any other lab’s) grading report. GIA uses terms, such as fancy light yellow, fancy yellow, fancy intense yellow and fancy vivid yellow, among others.
- Cape diamonds – generally within the range of M to Z on the color grading scale.
Again, this is not a technical term used on GIA grading reports.
- Carat weight – the measure of weight of a diamond.
Measure your diamond size with our Diamond Calculator.
It should not be confused with karat (the measure of the purity of gold). The name Carat is derived from the carob seed, which, given its fairly uniform size, was used hundreds of years ago to weigh diamonds and other precious stones. Given the imprecise nature of this measure of weight, a standardized measure of the carat was developed and is now the standard world wide weight measure for diamonds. A carat is equal to 0.2 grams.
- Carbon Spots – common term for black or dark inclusions in a diamond.
The technical name for them is black pique. Black pique are more detrimental to a diamond’s value than white or clear imperfections, as they are often more eye visible.
Cavity – An open imperfection in a diamond.
- Certificate – Some labs refer to their grading reports as certificates.
They are often laminated (for longevity and to prevent tampering) and provide written documentation of the diamond’s natural occurrence, weight, proportions, color grade, clarity grade, cut grade, and other characteristics and qualities of the diamond, including any treatments.
- Chip – an inclusion on the surface of the diamond where a piece of the diamond has broken off.
This can be quite detrimental to the value of the diamond, as the diamond needs re-cutting to return it to its original state. This can lead to the diamond ‘breaking its weight’ (going below important or magic weight levels, such a 1.00 cts).
- Clarity – a diamonds relative lack of clarity characteristics.
Inclusions (fully enclosed within the diamond) and blemishes (surface imperfections) determine clarity. A clarity grade is determined by the overall effect of the clarity characteristics. Specifically, the size, number, position, nature and relief of the characteristics are all factors.
- Size: A large inclusion makes for more of an inferior grade than a small one.
- Number: Generally, the more inclusions the worse the clarity grade. Though, one large inclusion can be worse than several small ones.
- Position: An inclusion under the table (in the center of the diamond) is more visible than one on near the girdle and thus would be more detrimental to the clarity grade.
- Nature: The type of inclusion can determine the clarity grade. A feather that runs from the crown through the girdle will result in a far worse clarity grade than a crystal in the crown.
- Relief: Most inclusions are white or colorless, but some are black or even red. Dark inclusions are more visible and thus factor more into the clarity grade. A red inclusion might look unique and interesting, but it will result in a lower clarity grade than if the same inclusion were colorless.
- Clarity Enhancement – Man-made actions to artificially improve a diamond’s appearance
Man-made actions (other than cutting and polishing) to artificially improve a diamond’s appearance and or clarity grade (whether temporarily or otherwise). Treatments can include fracture filling or laser drilling.
- Cleavage – a large, straight break or inclusion in the diamond along a plane.
- Cloudy – a state in a diamond caused by many small inclusions.
A state in a diamond often caused by so many small inclusions that it looks like a single, white “cloud”. While the cloudy appearance should affect the clarity grade, it is certainly quite detrimental to the value of the diamond.
- Color – a diamond’s color grade is based on its depth of color.
Diamonds that range from colorless (D) to light yellow (Z) or light brown fall into the D-Z grading range. Beyond the Z grade, you have fancy color grades, such as fancy light yellow or fancy light blue, fancy red, fancy intense blue, fancy vivid pink, fancy dark blue and fancy deep pink. Fancy red diamonds are extremely rare. Indeed, the largest ever graded by the GIA is “just” 5.11 cts, but is undoubtedly worth millions of dollars per carat. Fancy blue diamonds are also extremely rare. A 7.03 ct vivid blue sold in 2009 for $9.5mm or $1.35mm per carat. Fancy pink diamonds are also very rare. A 5.29 ct fancy intense pink was sold in 2009 for $388,000 per carat. A 5 ct D flawless (IF), on the other hand, is worth approximately $800,000 or $150,000 per carat.
- Color Enhancement – man-made action to improve or change a diamond.
Another man-made action to improve or change a diamond (whether temporarily or otherwise). Methods of color enhancement include High Pressure High Temperature treatment (HPHT), irradiation or the use of a coating to add color. The first two are usually permanent enhancements, while the latter can be removed through polishing or boiling the diamond in acid. Color enhanced diamonds are worth far less than non-color enhanced diamonds.
- Condition – State of repair.
Mint condition (no chips, nicks, abrasions, etc.), damaged (chipped, abraded, nicked, etc.) or broken (material (10%+) portion of diamond missing)
- Crown – the upper portion of a diamond (above the girdle).
See diamond graphic on the Diamond Weight Calculator page.
- Crystal – an inclusion within a diamond that looks like a bubble.
Occurrence will affect the clarity grade.
- Cubic Zirconium (CZ or Cubic Zirconia) – a synthetic stone made to simulate a diamond.
A synthetic (man-made) stone made to simulate a diamond. Made from zirconium dioxide, CZ can be distinguished from diamond by various means.
See Diamond or Fake?.
- Culet – the facet on the very bottom of a diamond, at the bottom of the pavillion.
The 58th facet on a round brilliant. The most modern cuts of diamond are now, typically, cut with no culet, while Old European cuts would tend to have large culets. A noticeable culet, in recent times, can be detrimental to value.
- Cushion Cut – See Shape.
- Cut – the cut of a diamond refers to its proportions and finish.
The cut of a diamond refers to its proportions and finish and is often referred to as the “make” of the diamond. The angles of the facets, the symmetry of the diamond and the quality of the polish all affect the cut grade. A visual assessment of the diamond can give a good indication of the cut grade, though measurement of the facets and various angles is required for a truly accurate grading. For example, the amount of brightness (or brilliance) a diamond exudes gives a good indication of the grade; the brighter the diamond, generally the better the cut grade. GIA’s cut grades for round brilliant diamonds range from Excellent (EX) to Very Good (VG) to Good (G) to Fair (F) to Poor (P). GIA does not give cut grades on fancy shaped diamonds (i.e. non-rounds).