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 |
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.