This is actually a report given by an independent gemological laboratory. There are a number of gemological laboratories which hand out these certificates.

However, only a few are respected by the whole diamond industry. The most well-known are the European Gemological Laboratories (EGL) and the Gemological Institute of America (GIA).

Individual stones

Each diamond is unique. This individual evaluation is strictly for the diamond’s quality, not its value.

The certificate maps out inclusions (imperfections), which are hand-drawn. This authenticates the diamond’s unique identity, since no two stones are exactly alike.

Certificate details

The first information (alongside the issue date of the report) is the Stone ID. This is a unique number assigned to your diamond and registered in a global database.

Next listed is the diamond’s cut and shape. If the shape is different from the standard round brilliant, it is called a fancy shape.

The dimensions are listed down as “largest diameter – smallest diameter X depth” for the round shapes. The others are listed as “length X width X depth”.

The weight is listed in carats, the standard unit of weights used for gemstones. (One carat is 200 milligrams.)

The grain lines reflect irregularities in the crystal structure. These are reported as colorless, white, colored or reflective.

The angles and measurements of the diamond that determine its optical properties are duly noted. Table size, crown angle and pavilion depth affect the stone’s appearance.

The certificate indicates the thickness of the girdle (the outside edge of the stone) relative to the diamond’s size, and whether it is polished or faceted.

The culet (the stone’s bottom point) is listed either faceted or not. If faceted, it is noted relative to the size of the stone.

The grades of the diamond’s finish and polish are noted and described including the symmetry. Color is graded, too, from D (colorless) all the way to Z (yellow).

Symmetry is the arrangement of the stone’s facets (surfaces) and finished angles. Grading reports describe them accordingly, whether they are excellent, very good, good, fair or poor.

The cut is listed as well as the quality of the stone’s clarity. The clarity is the absence of inclusions (blemishes) and graded from “flawless” to “included” based on the size, nature, position and quantity of the inclusions.

The certificate also notes the pavilion depth (distance from the girdle to the culet) which affects brilliance. Deviations from the Tolkowsky ideal cut are also carefully documented.

Most diamonds “fluoresce” (showing whitish, yellowish, or bluish tint) when exposed to ultraviolet light. They are only stated in the report, not graded.

Finally, there is a diagram on the certificate that approximates the shape and cut of the diamond. It has markings (in symbols) that include the type, nature, position, and approximate size of a clarity characteristic.

Gem quality

Coming from a leading gemological laboratory (the EGL mark appears under ultraviolet light), the certificate will ensure that your diamond jewelry has the quality you paid for. Do your diamonds have certificates?

Like any other natural stone, however, diamonds come in several shades of colors that are beautiful in themselves.

So far, there is a good range of colors in diamonds, aside from the in-demand blue and pink. Commercially available now are yellow, orange, green, champagne, grey, black, white, red, purple, chameleon and violet diamonds.

Absence of color and perfection

Among jewelers, the finest diamond stones are those that are totally colorless. They are graded D, meaning they are absolutely free of any color.

Theoretically, a chemically pure and structurally perfect diamond is also perfectly transparent with no color whatsoever. However, a good number of all the diamonds used as gems are imperfect.

A tinge of color

The next group are stones with very slight traces of color which can be seen by a diamond expert. When assembled into a finished jewelry, the color shades of these stones usually cannot be discerned anymore. Still, they are graded as E or F color diamonds.

Down the line, those stones which show very little traces of color are categorized as G or H color diamonds, or perhaps I or J color, depending on the strength of the color seen.

Grading and color

Those stones that are graded between D and F are considered “colorless”. Those that belong in the G to J group are called “near-colorless”. Those within the K to M grading are “slightly colored” and the N to Y stones usually looked like light yellow or brown.

One peculiar twist to the rule – those diamond stones graded Z are also rare and those bright yellow diamonds are priced higher than the ordinary.

The Gemological Institute of America (GIA) had developed the present color rating system for white diamonds (“D” down to “Z”, according to the intensity of the coloration). This has been universally recognized and adapted, overriding the previous older systems.

Fancy

The industry considers diamonds with intense colorations as “fancy”. An intense yellow coloration is regarded as one of the fancy colors and belongs to a different color grading system.

Gemologists have another rating system for fancy colored diamonds that is different from that used in white diamonds. However, this is not commonly used because these stones are relatively rare.

The color seen in the stones either detract or enhance its value, depending on the color itself and the intensity of the coloration. Examples would include the grade Z bright yellow, or an intense pink or blue in the stones, each one of which commands a better price.

Impurities

There are reasons for these colors in the stones. They could be structural defects in the crystal lattice of the stone or it could be a result of some chemical impurities.

Nitrogen is the most common impurity. It sometimes replaces a small proportion of carbon atoms in the diamond causing a yellowish or brownish tone.

Many impurities and structural flaws produce different colorations in the diamonds. Impurities are almost always present in white diamonds. It is not detectable in the rarest stones.

As always, choosing your diamond jewelry always go back to your own prerogatives on the pros and cons of owning either colored or white diamonds.