• Developing Brilliance: A Short History of Diamond Cutting

Developing Brilliance: A Short History of Diamond Cutting

Developing Brilliance: A Short History of Diamond Cutting

Prior to the fourteenth century diamonds were usually set into jewellery in their rough form, commonly an octahedral shape looking like two four-sided pyramids placed base to base and often with a beautifully bright lustre.  This was because diamond’s supreme hardness meant that traditional polishing media such as emery would not work. 

A breakthrough came in the jewellery-producing regions of what is now northern Italy when it was discovered that crushed diamond powder could be used as a medium for polishing diamonds.  This works because diamond possesses a property called differential hardness meaning that it is harder in some directions than others.  The crystals in the diamond powder are randomly orientated so some of them will always have the hardest direction outermost allowing the softer directions of another crystal to be polished.  This meant the pointed top of the crystal could be polished away creating a flat surface or facet across the top of the stone; this is the table facet which is still present in a round brilliant cut today.  The point at the base of the crystal would sometimes also be polished away to form a flat, reflective surface known as a culet. 

Over time more facets were added, polishing away the four edges of the crystal so that the table facet was surrounded by eight angled facets on the top of the stone.  This helped to minimise the risk of breakage as well as increasing the number of surfaces light could reflect from.  As cutters realised that increased sparkle could be achieved by adding more facets to reflect light around the stone the cut developed into the Old Mine cut.  This was cushion-shaped in outline (squarish with rounded edges) and both the upper (crown) and lower (pavilion) parts of the stone were covered in small triangular and kite-shaped facets.  This remained the standard cut until developments in technology from the nineteenth century onwards. 

The first major change came with the invention of mechanical bruting in the 1820s.  This technique rotated two diamonds against each other to grind the girdles (the widest part of the stone joining the crown and pavilion) and form a round shape.  For the first time diamonds could have their now-familiar round outline.  These new round stones were known as Old European cuts and were like Old Mine cut stones apart from their outline. 

In the early twentieth century the diamond saw was invented.  This allowed rough diamonds to be sawn down into smaller pieces prior to shaping.  Before this the only way to separate the rough crystals was cleaving and this could only happen in certain directions (planes of relative weakness in the crystal structure).  Sawing meant that a typical octahedral crystal could be separated into two parts, allowing two stones (one larger than the other) to be cut from it.  This development was significant because it allowed more efficient use to be made of the material cutters received and meant more smaller stones became available for use in jewellery.  Also, more attention could be paid to the quality of the cut instead of just how much weight could be retained from the original crystal. 

The images above show the development from an old cut (left), through a transitional old brilliant cut with additional precision(centre, middle stone) to a modern round brilliant cut (right).

From this point on work went into perfecting the angles and proportions that would produce the best return of brilliance and fire from the diamond.  Pioneers like Marcel Tolkowsky applied scientific methods and mathematical thinking to the problem.  Tolkowsky’s work is still the basis of the so-called (although not by him) ‘ideal’ round brilliant cut.  Stones cut to these proportions have larger table facets, shallower crowns and no culet.  The angles that the crown and pavilion meet the girdle are very particular; the intent is to produce total internal reflection where light that enters the diamond though the crown is reflected off the pavilion facets and back out through the crown.  This is what produces brilliance; the return of white light by the diamond. 

With a few tweaks and minor adjustments this is the modern round brilliant cut.  Most diamonds now diverge very little from this pattern although some brands have developed their own variations with additional facets or slightly different facet patterns.  The work that has taken place over centuries, and the last 200 years in particular, has refined the shape and pattern of the round brilliant cut to produce the best balance of brilliance and fire, making the most beautiful, sparkling diamond.       

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