GIA is trusted to grade the world’s most famous diamonds, and we apply the same expert standards to your diamond.
GIA rigorously examines every diamond to identify laboratory-grown diamonds (also known as synthetic or man-made diamonds), diamond simulants and all known treatments. Professional gemologists examine each diamond under strictly controlled lighting and viewing conditions to provide the most rigorous evaluation of the 4Cs of diamonds.
Diamond Color Grading
Because light sources and backgrounds have a significant impact on a diamond’s appearance, GIA uses master stones in a standardized viewing environment to determine diamond color grades. GIA assigns at least two color graders to enter the same diamond’s color data. For inconsistent results or diamonds of unusual weight and quality, GIA assigns more graders to enter color grade opinions. The grade is not finalized until there is enough agreement.
To provide a common basis for diamond color comparison, GIA gemologists put together a set of master stones that represent different color grades in the GIA grading scale. Each stone in the set represents a letter grade. The master stones are placed in the grading tray from left to right, table top down.
Diamond Clarity Grading
Diamond clarity grading is done under standard viewing conditions using a 10x magnifying glass. The initial inspection grader will carefully examine the diamond to determine the clarity/finishing characteristics of the diamond and to look for evidence of clarity treatments such as laser drilling or fracture filling.
At least two GIA graders evaluate the diamond’s clarity, polish and symmetry. Their clarity characteristics are then plotted on a diagram that best depicts the diamond’s shape and faceting style.
GIA laboratory graders observe a diamond’s clarity characteristics under magnification.
Diamond Cut Grading
GIA provides cut grades for standard round brilliant diamonds in the D-to-Z color range . To develop its cut grade system, GIA conducted extensive computer modeling of round brilliant diamonds over a 15-year period and verified its findings with more than 70,000 observations of natural diamonds. The system can now predict cut grades for more than 38.5 million diamond proportion settings.
GIA’s Excellent to Poor Cut Diamond Grading System evaluates a diamond’s overall face-up appearance to predict the intensity levels of brightness, fire and scintillation (how bright and how it interacts with light). GIA also screens every diamond submitted to determine if it is a laboratory-grown diamond.
Round brilliant diamonds show how the quality of a diamond’s cut affects its appearance. From left to right, these diamonds are: Poor Cut, Good Cut, Excellent Cut.
Diamond Carat Weight Measurement
GIA determines the carat weight of diamonds by weighing them on a very precise electronic microbalance that measures to five decimal places (approximately 1/10,000 of a carat). An optical measuring device is used to determine the diamond’s proportions, dimensions and facet angles.
Graders in the GIA laboratory use a grading system to determine a diamond’s carat weight.
