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Diamonds – Facet Definition

Sep 29th, 2015

Diamonds – Facet Definition

‘a diamond is only as good as its worst facet’-Mb

 

Making Every Facet Count

Every facet on a diamond fulfils 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 would compromise light reflection. After all, any diamond is only as good as its worst facet.

Facet Definition

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, similar to what we have on a round brilliant diamond.  The azimuth for facets on a 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. All photos 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.

To illustrate this principle further, have a look at the following images that were created in GemCad. As can be seen from the top and bottom view, all the facets are in alignment, until one looks at the profile views!

This is how they do it

Natural on pavilion

First facet made steeper and azimuth moved away from main facet

Second facet made steeper and azimuth moving away from the adjoining main to ‘correct’ the rib line.

First crown facet dug out by making it steeper and moving the azimuth away from the main.

Second facet cut steeper and azimuth moved away from adjoining main to ‘correct’ the rib line.

New Designs

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 often leads to undesirable results.By adhering to the principles of properfacet definition, new designs have been and can be created with spectacular results. Ignoring the principles of proper facet definition, could lead to theSardine Effect.

All the facets are neatly packed, but very,very dead!

Multiple Tier Pavilions

Multiple tier pavilion faceting is the key to add more facets to the pavilions of diamonds to enhance their visual appeal. This also normalizes the facet area to facet count ratio on a diamond. For instance the surface area of the pavilion of an ideal cut round brilliant is approximately 53% of the total surface area of a diamond  but has only 24 facets  for a ratio of 53:24, while the crown represents around 30% yet has 32 facets. The table and the girdle make up the balance of the surface are. By doubling the facets on a pavilion to 48 we get a much more favorable facet to surface are ratio 48:53, which is more in line with the ratio of the crown facets. After all, the pavilion facets are the work horses on a diamond and surely there is more than enough ‘real estate’ on the pavilion to add facets that really matter. However the principle of proper facet definition needs to be borne in mind when new designs are created.

For for more information contact Mike Botha

mike@embeediatech.ca 

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