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Pavilion Depth

In order to explain the important function of the pavilion facets, Fig 238 shows that the light falling from above into a brilliant can only be reflected back by total internal reflection on the pavilion facets, if the angle between the pavilion facets and the girdle (designated by y) corresponds to the ideal size. In the Practical Fine Cut this angle amounts to 40.8° and the pavilion depth to 43.4 % of the girdle diameter. The pavilion angle changes with increasing height of the pavilion, as follows:

Pavilion depth Pavilion angle
40% 38.7°
41% 39.4°
42% 40.0°
43% 40.7°
44% 41.3°
45% 42.0°
Fig 238 The depth of the pavilion is decisive for the refraction of light in a diamond Fig 238 The depth of the pavilion is decisive for the refraction of light in a diamond Fig 238 The depth of the pavilion is decisive for the refraction of light in a diamond
Fig 238 The depth of the pavilion is decisive for the refraction of light in a diamond

For quick checking of the pavilion depth visual aids are likewise available by means of which the depth can be very accurately estimated by eye.

Girdle thickness Sideways reflection to estimate pavilion depth