Tolkowsky - Ideal Cuts
Most of a diamond's sparkle and liveliness comes from its cut. Rough diamonds are often cut to retain carat weight, which results in light leaking out the back of the diamond, and often produces a dull lifeless diamond with a smaller diameter.
In 1919, Marcel Tolkowsky (an engineer by education and member of a Belgian family of diamond cutters) wrote a masters thesis on the ideal proportions for round diamonds. The ideal proportions designated by Tolkowsky were derived from mathematical calculations that considered both the fire and brilliance of the stone and have generally been considered as well chosen and have been the benchmark in the industry for the past 80 years. The target set by Tolkowsky was of a diamond with crown angle of 34.5 degree, pavilion 40.75 degree, and table of 53 percent.
Tolkowsky's 'ideal proportions' were intended as a set of general guidelines as certain aspects of a diamond's cut had not been taken into consideration or explored. Tolkowsky's ideal design has lead to contemporary marketing inaccurately labelling diamonds as not all diamonds within the designated tolerances could be as "ideal". Studies have shown that diamonds outside of the proportions indicated by Tolkowsky that are equally or even more beautiful.
Diamond cut grading systems were developed in order to classify and differential high quality cuts from cuts of lesser quality. However, as existing cut grading systems are generally based on the developed tolerances, they are inadequate. Further such systems are feature oriented in that they provide a numerical grading for the diamond. Laboratories that provide such a numerical grading take the worst scoring feature and assign that score as a cut grade. This process ignores the complex interrelationship of facets as light reflects and refracts on its passage through a diamond. A diamond with a slight deviation on each of these measures can rate as ideal even though the performance is only fair. Equally some deviations for Tolkowsky's proportions can compensate for other undesirable deviations in other factors.
The diamond trade is composed of numerous diamond traders around the world selling diamonds of varying quality. For the average consumer, evaluating diamonds, it can be a long and difficult process evaluating diamonds and judging their appearance based on the cut factors listed by the trader/retailer. The Holloway Cut Advisor is a system which has been developed whereby the various cuts of a diamond are defined in terms of individual user preferences. In other words, the various cuts of a diamond are assessed according to factors that characterize the beauty and desirability of the diamond.
In this regard, three factors are commonly used to assess the beauty of a diamond being brilliance, fire or dispersion and scintillation.
Brilliance: Brilliance is generally considered to be the most important feature when considering diamond beauty. If brilliance is compromised then the effectiveness of a diamond's fire and scintillation is also reduced. Brilliance is often related to proportions that reduce light loss from the pavilion of a diamond. The understanding of brilliance must include the directions in which light travels to an observer and the source and type of light used in any analysis.
Fire or Dispersion: Fire is the term used to describe the spectral separation or dispersion of white light into rainbow flashes. Fire is generally considered to be enhanced with steeper crown angles and smaller tables.
Scintillation: Scintillation is perhaps the least clearly defined visual feature in diamond appearance. One definition is "a pleasing visual balance in the spread of clearly defined and well spread dark and light areas that flash on and off as a light source, the stone or the observer's position change". The dark areas should be a small component of the overall stone's face up appearance with a head shadow of 21 degrees. Scintillation is dependent on the type of lighting, the observer's physical presence and the diamond itself. It is more personal than brilliance and fire, because the more of these two features the better, whereas the ideal amount of blackness and contrast is in the eye of the beholder.
