HISTORICAL

It will appear later that both the evolution of Diamond as a fiery Gemstone and also many of its applications as an indus­trial tool require us to be able to grind and polish a Diamond to some specially required shape. It has often wrongly been stated that the art of shaping and polishing Diamond was invented in Belgium in 1476 by Berghem of Bruges.

It was considered that he discovered that crushed Diamond grit when mixed with olive oil and smeared on to a rapidly rotating cast iron disc was able to grind and polish Diamond. This attribution to Berghem is manifestly quite incorrect, for not only is there documentary evidence from records of distinguished families which go back at least to 1412, listing jewellery incorporating polished Diamonds, there was further in fact a Diamond polishers' guild in Nuremburg before the time of Berghem, records going back to as early as 1373. A fully operating guild at this date surely implies that Diamond polishing in Europe was fully active certainly before a.d. 1300. Traditionally, the shaping of a Diamond is called ‘polishing’, the word being still used both for grinding a Diamond into shape as well as for producing a brilliant finish.

Early polishing of Diamond was restricted to production of two kinds of shape of a Diamond gem, due merely to the simple technological fact that the two types of faces involved are relatively 'soft' faces. These shapes were respectively the 'table' and the 'lozenge'. The table arose, as in Fig. 4, from grinding an octahedral Diamond on a cubic plane; the lozenge (Fig. 8) comes from grinding the dodecahedral plane.

The discovery which enabled a Diamond to be polished lies latent in the phrase 'Diamond cut Diamond'. This is based on a realisation of the different hardness properties in different directions. Suppose some Diamond is crushed into a powder and then this powder is rubbed or impregnated into a rotating wheel. Clearly, amongst the innumerable particles on the wheel many will present their 'hard' directions. Suppose we offer to this wheel a 'soft' plane or direction on a Diamond, then, slowly, but with certainty, the hard regions on the particles will wear away the soft area offered. So the Diamond offered can be ground to shape. If we use coarse particles on the wheel the cutting action will be fast and it is called, often, grinding. If we use very fine powder, the cutting action is slow and instead the surface takes on a brilliant polish, the famous adamantine lustre.

It is a remarkable fact that Diamond polishing has remained virtually unchanged for at least 400 years. Today the Diamond polisher uses the identical tools and methods which were employed in the Middle Ages. The only two real innovations have been (a) the introduction of electric motors to drive the polishing wheels, (b) the use of Diamond-slitting saws (of which more anon).