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Square proprietary cuts
Square proprietary cuts

Square proprietary cuts

Square proprietary cuts are popular with cutters because they have a very high yield from an octahedron rough. GARRY HOLLOWAY reports.
An octahedron crystal is sawn in half, so the crown of the larger stone is already in place, with a smaller stone polished from the remainder (see image 4, above). If the octahedron has all its corners intact, then two princess cuts can be polished, with the yield as high as 80 per cent. So a one-carat rough can yield as much as two 0.40-carat princess cuts with a total weight of 0.80-carats.

This explains why one-carat, square, fancy-shape diamonds cost around 30 per cent less than rounds, which typically have total yields of only 45 to 50 per cent.

If the octahedron has a few damaged points or inclusions in that area, then it is common to polish one or more diamonds with “cut corners”, like a radiant cut.

The octahedron is a common crystal habit for diamond. This shape is called a “sawable” because the stone is usually sawn into two stones, as opposed to a “makeable”, (a rough diamond that will be polished into a single stone). It can be sawn right on the edge into two equal halves, with the saw plane becoming the table of each diamond. (See image 4.)

Sometimes the saw blade is run just above half way, leaving the thickness of the crown height to make one diamond a little heavier.

As shown in the images of a rough diamond, this also helps explain why many cuts, and princess cuts in particular, tend to have very large tables. In fact, princess-cut tables are usually too large by 5 to 20 per cent more than the optimum. Sometimes the crown height is so low that it reduces optical performance.

The first square (and rectangular) outline diamonds to be cut were the step-cut family, where the facets run parallel to the outside edge. These include Carré (small square cuts), bagutte and emerald cuts. The next article in this series will cover that family.

The radiant cut article, featured in November 2008, discussed how the radiant cut (first patented in 1976) is one of the more recent diamond cuts and was the first rectangular or square cut to have a complete brilliant facet pattern applied to both the crown and pavilion. This cut presented more sparkle than the emerald step cut.

The princess cut article (March 2008) mentioned how this cut was designed as a square version of the round-brilliant cut, also known as a square modified-brilliant. The goal of its development was to achieve the weight retention of emerald step cuts when cutting from octahedral crystal rough, and the superior scintillation and -brilliance of the round-brilliant cut.

These are a princess cut’s selling points – a bigger carat weight, for less money and plenty of sparkle.

The Regent is a square, proprietary, hearts and arrows cut designed to show the same hearts and arrows patterns as round brilliant cuts (see images 2 and 3).

It is important to remember that the eight faces of an octahedra (four crystal plane directions because the opposite sides are parallel) are also the easiest cleavage direction and as such, all square cuts are prone to chipping from the girdle edges during setting. For that reason it is a good idea to suggest rings to clients that are insured. Slightly thick to thick girdles are less likely to chip. Chipping can also become an issue with sharp corners – 90 degree corners – such as the princess cut.

Buyers should also be aware of Fish-Eyes (girdle reflections). It is a good idea to have a comparison stone to compare these stones for brilliance, fire and scintillation.











ABOUT THE AUTHOR
Garry Holloway

Diamond Cut Expert • Holloway Diamonds


Australian-born Garry Holloway is a self confessed “cut nut”. He graduated as a Geologist in 1973 and in 1975 he established two fine jewellery stores in Melbourne. While studying for the Diamond Diploma in 1984, Holloway became obsessed with diamond cut research; he invented the Ideal-Scope and Patented Holloway Cut Advisor. Holloway lectures on diamond cut at the Gemmological Association of Australia and works with a group of Russian and Indian researchers known as The Cut Group. Visit: hollowaydiamonds.com.au

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Friday, 23 August, 2019 04:23pm
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