Diamond certificates for dummies
A crash course in decifering the document

"Get it in writing," says Sharrie Woodring, EGL USA's Senior Gemologist. It's a common piece of advice. Fortunately, a diamond certificate-a professional gemological evaluation of the stone's unique characteristics-does just that. Think of a certificate as an owner's manual for your diamond. And then acquaint yourself with the subtle nuances that made you fall in love with your particular gem. Confused by the technical jargon? Following is a step-by-step guide from EGL USA for demystifying the diamond certificate.

Certificate Number:
Each gemstone submitted to a gemological laboratory is assigned an identification number for tracking purposes. Often the ID number will be laser inscribed on the diamond. At EGL USA, all ID numbers have a two-letter prefix: 'US' in its New York and Los Angeles offices and 'CA' in Vancouver and Toronto. Consumers can verify their certificates on-line at www.EGLUSA.com.

Weight:
Diamonds are weighed in carats. One carat equals 0.20 grams. EGL USA uses the international standard for weighing diamonds. The weight is rounded up only when the third decimal place is 9; otherwise the weight is rounded down. For example: 0.998 carats is reported as 0.99 carats, and 0.999 carats is reported as 1.00 carat.

Shape and Cut:
Shape refers to the outline form of the diamond. Round, oval and marquise are a few popular shapes. Cut describes the style and arrangement of facets, or how a diamond is proportioned for maximum sparkle. Brilliant cuts are comprised of triangular and kite-shaped facets. Step cuts consist mostly of rectangular shaped-facets.

Measurements:
Diamonds are measured in millimeters and typically recorded to a hundredth of a millimeter. The measurements are stated as Maximum x Minimum x Depth for round diamonds or Length x Width x Depth for fancy-shape diamonds.

Proportions:
As important as color and clarity grades, proportions influence the brilliance and fire of a diamond. Proportions include:

• Depth: The depth percentage is a comparison of a diamond's total depth to its total width. For a round brilliant cut diamond, a depth percentage in the range of 57.0% to 63.5% is considered ideal.
  
  
• Table: The table is the largest facet on the top of a polished diamond. The table percentage is a comparison of the size of the table facet to the width of the diamond. A table percentage in the range of 53% to 63% is considered ideal for modern round brilliants, while old European cut diamonds typically have a smaller table, ranging from 49% to 53%.
  
  
• Crown: Looking at a diamond in profile, the crown refers to the upper portion of the diamond from the girdle to the table. The crown percentage is a comparison of the height of the crown to the total depth of the diamond.
  
  
• Pavilion: When viewing a diamond in profile, the pavilion refers to the lower portion of the diamond from the girdle to the culet. The pavilion percentage is a comparison of the height of the pavilion to the total depth of the diamond.
  
  
• Girdle: Looking at a diamond's profile, the girdle is the narrow band, around the widest part of a diamond, separating the crown and the pavilion. Girdle thickness ranges from extremely thin to extremely thick. It is best to have a girdle in the range of thin to slightly thick; an extremely thin girdle is a durability issue and an extremely thick one detracts from the diamond's beauty. Girdles can be faceted, polished, or left unpolished.
  
  
• Culet: The culet (pronounced cue-let) is the facet on the point at the bottom of a diamond. Most modern-cut diamonds do not have a faceted culet, which is described as 'None' on the certificate. Pointed to small faceted culets are preferable, however, older diamonds often have a larger culet, which is an acceptable feature of an antique cut.
  

Polish:
The polish of a diamond describes the quality of the faceted surface. Features such burn marks and polishing lines negatively affect a diamond's polish grade. EGL USA uses the terms 'Poor,' 'Fair,' 'Good,' 'Very Good,' and 'Excellent' when grading polish.

Symmetry:
The symmetry of a diamond refers to the exactness of the facet arrangement. Features that are considered when grading symmetry include: how precisely the facet junctions come together, how closely the facets of the crown and pavilion line up, and whether the shape's outline is symmetrical. EGL USA uses the terms 'Poor,' 'Fair,' 'Good,' 'Very Good,' and 'Excellent' to grade symmetry.

Clarity Grade:
Clarity specifies the degree to which a diamond is free from nature's "birthmarks," or tiny, generally microscopic imperfections that make each diamond unique. Diamonds are assigned clarity grades based on what can be detected with ten-power magnification. Diamonds with relatively few clarity characteristics are very rare. See the cover of the EGL USA certificate for a description of each grade.

Color Grade:
Color grading involves carefully comparing the ungraded diamond, under scientifically calibrated lighting conditions, to a special master set of diamonds with known color grades. The grading system ranges from D (colorless) to Z (obvious color but not considered a "fancy" colored diamond). The nuances between color grades are very subtle, and color grading requires extremely accurate color vision. Two color graders plus a final grader must agree on the diamond's color before the color grade is assigned. See the cover of the EGL USA certificate for the color grading scale.

Fluorescence:
Diamonds often emit a color reaction when subjected to ultraviolet light. EGL USA grades fluorescence on a scale from 'None' to 'Very Strong.' Most often diamonds fluoresce a blue color, however other colors are possible. If the fluorescence of a diamond is stronger than 'Faint,' EGL USA will note the color of the fluorescence on the report. Fluorescence can add an interesting quality to a diamond, however, a very strong fluorescence can affect its value.