The term cut is commonly interchanged with the term shape of a diamond. Many dealers today use the word “cut” referring to the shape but for the purposes of clear understanding in this course and in your trade practices the… Continue reading →

A unique one hundred facet round brilliant cut. The image to the left illustrates a “modern round brilliant cut” but the same term can apply to all other brilliant cuts, (pear shape brilliant, oval shape brilliant, etc.?). Step-cuts, such as… Continue reading →

Reflected light does not enter the diamond.Transmitted light does enter the diamond.The concept of designing the modern brilliant cut was to formulate an optimum angle, depth and table percentage relationship. The properties that had to be understood to accomplish this… Continue reading →

Different gems or substances have varying refractive indexes. Diamond’s is unique in the sense that it has the high refractive index of 2.417. Cubic zirconia’s is about 2.15. The higher the RI (refractive index) the more ability it has to… Continue reading →

Looking for a doubling effect of the culet through a crown bezel facet in a doubly refractive stone. The axis orientation (rough layout) will determine the direction of view.   As pictured the individual colors of the spectrum all bend… Continue reading →

The reflected light presents an angle that is equal to that of the incident light.The design of the modern round brilliant is such that it “contains” the light that enters it as long as possible. To understand this, we must… Continue reading →

Transmitted light enters the diamond due to its steep approach to the surface. This part is a little more involved — but not much. Transmitted light is the portion of light that enters the material, or a diamond in this… Continue reading →

The modern cut was designed in a way to contain the light travel path avoiding the pathway of escape within the critical angle 24.5 degrees pictured as a cone.The crown angles on a modern cut were designed to allow the… Continue reading →

With steep pavilion angles, the light exits after first reflecting once. Note that the angle of incidence falls within the 24.5 degreesThe original ideal pavilion angle is 40.75 degrees. The major gem labs do agree that slight variations from this… Continue reading →

The original ideal angle for the crown is 34.5 degrees. Here again, the major gem labs do agree that slight variations from this angle will still produce a well-cut diamond. This angle was designed to provide the final escape route for the reflected internal light so that the dispersion and brilliance could be viewed. It was also important to provide an angle great enough for light to enter and exit from more diverse directions. Continue reading →

A diamond cutter’s star gauge used to measure crown angles.Diamond cutters use a star gauge to measure the crown angle from the table, which should –if the stone is accurately cut — coincide with the crown’s angle to the girdle… Continue reading →

A proportionscope is used to determine angles and percentages of the stone.A proportionscope, first designed and manufactured by GIA in 1967, is an instrument that casts a silhouetted image of the diamond It allows us to check the proportions of… Continue reading →