Every facet on a diamond fulfills a specific function. The crown facets are the ‘windows’ of the diamond which let light enter and exit a diamond. The pavilion facets are the ‘work horses’ that reflect light back through the crown facets. It is important that facets be placed in the correct positions and on the correct angles to perform their task effectively. The crown and pavilion facets have to line up perfectly. Also, all the facets have to be polished, so that they are free of any polish lines, abrasions or other surface anomalies that could compromise light reflection. After all, any diamond is only as good as its worst facet.
Facets need to be properly defined in terms of their azimuth to each other (radial position) and their angle in relation to the table facet of the diamond. This principle is called Facet Definition. For example the azimuth (radial position) of the numerals on a clock is 30 degrees (360°÷12). Likewise, if we were to cut a pizza into two equal parts, the azimuth for the two halves would be 180°. Divide it into quarters and the azimuth would be 90°. If we continue to divide we would get 45°, 22.5° and 11.25°. Dividing the pizza into 32 parts (360°÷32=11.25°) would yield 32 pieces of 11.25° each. The azimuth for facets on a round brilliant diamond is at least 11.25° or multiples thereof. Below is a diagram of the azimuth of facets on a round brilliant.
Painting and Digging
Polishers would often alter the azimuth by either decreasing the azimuth between facets, which is known as ‘painting’ to preserve extra weight or they would increase the azimuth between facets, which is known as ‘digging’ to improve clarity or to remove naturals without having to re-cut the whole diamond, leading to a net weight saving. Both painting and digging messes with the azimuth and leads to compromised facet definition and light return. Following are photographs of painting and digging in their various combinations. Besides normal, there are 8 combinations of painting and digging which cutters employ to achieve a specific objective. It is not a sign of poor cutting skills, on the contrary, it takes more skill than to cut a diamond with normal azimuth. Painting and digging will always compromise symmetry and light return. All photos of the diamond which we call ‘Dig Painter’ were taken by Branko Deljanin - Swiss Canadian Gem Lab, Vancouver Canada.
Image 1 - Crown girdle facets are normal and the pavilion girdle facets are dug-out.
Image 2 - Crown girdle facets are dug-out and pavilion girdle facets are normal.
Image 3 – Crown and pavilion girdle facets are dug-out.
Image 4 – Crown and pavilion girdle facets are painted.
Image 5 – Crown girdle facets are dug-out and pavilion girdle facets are painted.
Image 6 – Crown girdle facets are normal and pavilion girdle facets are painted.
Image 7 – Crown girdle facets are painted and pavilion girdle facets are dug-out.
Image 8 – Crown girdle facets are painted and pavilion girdle facets are normal.
Designers would often use the principles of painting and digging to come up with new facet arrangements for new designs. This is however a kiss of death for the diamond and may lead to diamonds having too much or not enough contrast or worse still, light leakage. Facets are often added that do nothing for the diamond and which leads to undesirable results. By adhering to the principles of proper facet definition, new designs have been and can be created with spectacular results.