Diamond Proportions

Diamonds Index

Ideal Proportions

Too Deep

Too Shallow

Depth
The first, and probably most important aspect of the proportion of any polished diamond is its depth relative to its diameter. It is also the easiest to measure.

Tolkowsky
Marcel Tolkowsky made calculations about light travelling through diamonds, using ray tracing. His work is considered limited today, and there had been studies of diamond proportion before his time, certainly from 1751, and well-proportioned diamonds were already being produced by Henry Morse and Charles Field. Tolkowsky was however the first to apply scientific principles and publish the results. These were in a book called "Diamond Design, A Study of the Reflection and Refraction of Light in a Diamond", published in 1919.
Tolkowsky studies were only two-dimensional, and ignored incident light from many different directions, and made a number of other simplifying assumptions. Others have followed and improved on his work since, but his basic conclusions and recommendations were approximately correct.

Simplified Scheme
The three simplified diagrams shown demonstrate what happens to light rays hitting diamonds which are well-proportioned, too deep, and too shallow, in turn. Each diagram shows two perpendicular rays, one entering through the table, the other entering through a kite or bezel facet. These diagrams ignore other important aspects such as the relative heights of the crown and pavilion to each other, and we intend to add further pages dealing with these proportions later. For now, let's consider:-

• Well Proportioned
  Tolkowsky did not use the term ideal, but this word is now used to describe a well-proportioned diamond. Both rays are reflected back through the crown (top) of the diamond towards the (presumed) viewer. This is obviously good.
• Too Deep
  The second diagram shows both rays exiting the diamond through the pavilion, and away from the viewer, and is undoubtedly not as good as in the first diagram. Many older cut diamonds are too deep, and this was done to maximise retained weight which is the same as minimising weight loss. The historic reason for this is that most rough diamonds are of deeper than ideal proportions.
• Too Shallow
  The third diagram shows one ray exiting downwards through the pavilion, and the other through the crown, but at a shallow angle, and one which would not been seen from a normal viewing position. This clearly is also not optimal.
  Some jeweller's sell "spread" stones as being a benefit to the customer, stating for example that a particular stone spreads (has a larger diameter) more than its weight. It is important to remember that very few things come free. If "spread" diamonds were better than ideal ones, then spread would have become the ideal.

Facet Names & Names of Other Parts of Polished Diamonds
Names and explains terms such as crown, pavilion, table, kite facet.

Diamond 4C's Tour - Next Stop - Colour