Thursday, May 7, 2009

How GIA Grades Diamonds

Diamond Carat Weight Measurement
To determine carats, the diamond is weighed using an extremely accurate electronic micro-balance that captures the weight to the precise fifth decimal place (the nearest ten-thousandth of a carat). An optical measuring device is used to determine the diamond’s proportions, measurements, and facet angles. This data is uploaded into GIA’s computerized operations and information database management system.

Grading Diamond Color
Since light source and background can have a significant impact on a diamond’s appearance, color is graded in a standardized viewing environment against color masters. A minimum of two color graders enter their independent evaluations into the system and depending on the agreement of these grades, and the weight and quality of the diamond, it may be sent to additional graders who enter their own color opinions. The grade is not determined until there is sufficient consensus.

Diamond Clarity Grade
Diamond clarity is graded under standard viewing conditions with 10× magnification. The preliminary grader carefully examines the diamond in order to identify clarity/finish characteristics and evidence of any clarity treatments such as fracture filling or laser drilling.

A minimum of two graders assigns their impression of the diamond’s clarity, polish, and symmetry. Next they plot the clarity characteristics on the diagram most representative of the diamond’s shape and faceting style, selected from a database of hundreds of digitally stored diagrams. Also during this process the stone is screened to determine if it is synthetic.

Diamond Cut Grading
provides a cut quality grade for standard round brilliant diamonds that fall into the D-to-Z color range. To develop their Cut Grading System, GIA performed extensive computer modeling of round brilliant diamonds over a 15 year period and conducted more than 70,000 observations on actual stones to validate the research. This system can now predict the cut grade for more than 38.5 million proportion sets.
GIA’s Diamond Cut Grading System assesses the diamond’s overall face-up appearance to predict the intensity levels of brightness, fire, and scintillation (the diamond’s sparkle and interplay with light). The result is a comprehensive Cut Grading System that accurately reflects all the critical cut factors of a round brilliant diamond.

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