PLINY

Our next important historical appreciation of the hardness of Diamond, and a more precise definition of its use as a tool is to be found in the great 37 volumes on natural history written by the Roman, Pliny, a work produced about a.d. 77. Volume 37 deals with precious stones, and very expert and knowledge­able is Pliny. We can recognise today exact descriptions of many of the minerals he knew of. Much of his work was obtained either from reading or from hearsay, and especially with regard to extremely rare materials like Diamond Pliny offers us a curious mixture of solid fact and airy fiction.

Yet the grain can be separated from the chaff because of our later knowledge of today and the grains of truth in Pliny are quite remarkable enough.

Many of the curious statements in his work are closely tied up with the truth. For instance, Pliny quotes what at first sounds a yarn. He says that when a diver goes down to the sea-bed off the coast (off Arabia perhaps) looking for pearl oysters, he fills his mouth with olive oil. When he reaches the bottom he throws back his head and releases the oil, whereby, says Pliny, he can now see the sea-bed more clearly. Now this queer tale typically reveals what is often to be found in Pliny, i.e. extremely good science. It is certainly true, for the oil rises to the surface and spreads rapidly to form an oil slick above the head of the diver. But we all know about pouring oil on troubled waters! Indeed, the oil, acting by surface tension forces, reduces the surface ripples on the water and this has two consequences: first, more light penetrates to the bottom; second, the usual flicker created by ripples is reduced. Thus, as Pliny so correctly remarks, the diver has improved visibility in his hunt for oysters.

This is but one example from many of the curious reports in Pliny which are linked to truth. At times, however, truth is tied to incredulous myth, accepted too uncritically by our author. This was of course an age of belief in traveller's tales.

Pliny's writings on Diamond are certainly a curious mixture of good science and odd myth. We shall sift out and reject the obvious myth (such as the tales about the power of goat's blood over the strength of Diamond, and so on) and retain what we can now see is a sound report, based on good solid observation initially, then handed on, to reach Pliny ultimately.

Some writers maintain that when Pliny talked of ‘adamas’ he was not referring to Diamond, although what he is supposed to be talking about these authors do not venture to tell us, nor do they explain away the fact that Pliny is exactly describing properties which we do indeed now know are exactly demon­strable properties of Diamond. The name ‘adamas’ comes from

the Greek and means ‘unsubduable’, for, Pliny remarks, this material resists both fire and blows. This is not quite true, but it reflects common belief at the time and later. Pliny shows a good knowledge of quite a number of hard gemstones and is clearly familiar with the lapidary techniques needed for fabricating them into shapes, especially into lenticular shapes. He describes in recognizable detail, quartz, agate, ruby, emerald, and so on, and also how to shape them. Diamond, he says, resembles two cones united at the base, certainly an admirable description of the curved, rounded type of octa­hedron Diamond then being found in India, at the time the sole source of supply. It is the nearest correct description of a rounded octahedron one can anticipate in view of Pliny's lack of crystallographic terminology.

Then Pliny adds a telling phrase, 'Its hardness is beyond expression whilst at the same time it quite sets fire at defiance'. If we recall that Pliny was knowledgeable about such hard GEMS as emerald, ruby and agate, his insistence on the extraordinary hardness of adamas is in itself proof that he is talking of Diamond. But there is more to come. For Pliny goes on to say: ‘When by good fortune this stone does happen to be broken, it divides into fragments so minute as to be almost imperceptible.’

Now this is a striking remark, since we know (and will consider later in detail) that if Diamond be pounded with pestle and mortar it crushes down to an extremely fine grit (Pliny's 'imperceptible fragments'). For although Diamond is very hard, it is also brittle. Hardness and brittleness are quite separate properties. The Diamond will scratch an iron hammer, yet it can, with a vice, be pressed into iron as if the latter were soft as butter. Yet a sharp blow shatters it, because the impact initiates cleavage and fragmentation. Repeated blows break a Diamond down to powder so fine as to be 'imperceptible'.

Here again, then, Pliny is quite accurately describing what we do really know to be a physical property of Diamond. But now comes a remarkable sentence, following what Pliny has just said about the fragmentation of Diamond. For, remark­ably enough, Pliny goes on to say, 'These particles are held in great request by engravers who enclose them in iron and are

enabled thereby, with the greatest facility to cut the very hardest substances known' (my italics).

Here, 1900 years ago, we have for the first time a precise description of the preparation of what is now called a bonded Diamond tool, which, believe it or not, was first patented some 30-odd years ago! For Pliny tells us that if Diamond particles are 'enclosed' in iron we secure a formidable engraving and cutting tool. We shall see that 130 years ago a technique was again described (it was not new then) of hammering crushed Diamond into metal wheels for cutting and grinding hard gemstones. This is precisely Pliny's method and nothing more.

There is perhaps another point of much historical interest in this statement by Pliny, for note that he says this tool will ‘cut the very hardest substances known’. Now he himself had just maintained that Diamond was the very hardest substance known. Is it not implicit in this remark that this tool (iron impregnated with Diamond) will thus even cut Diamond itself! Maybe here we have the answer to the old mystery, the mystery of who invented the polishing, cutting and even engraving of Diamond.

There is some genuine evidence that possibly 1000 years back it was known in India that a rotating iron wheel impreg­nated with Diamond dust could be used to grind faces on Diamonds. Indeed, Tavernier in his 17th-century travels through India describes numerous polished Diamonds pre­pared thus, adding sardonically that the purpose of polishing a facet was neither for beauty nor for shape, but simply either to remove or to hide a defect. Indeed, he remarks drily that if any Diamond were offered to him with polished faces on it, he would search dilligently for the flaws they were sure to be hiding. It looks very much as if this knowledge of how to polish Diamond goes back much further, indeed to Pliny's time and of course even earlier, since he was reporting an already known technique.

Then again there has always been a strange mystery about certain Indian Diamonds which have had the names (and dates) of their Royal owners engraved upon them. On three different large Diamonds owned by Persian shahs are names, and the respective dates inscribed are 1619, 1628 and 1641. Now, there was simply no other way of so engraving a Diamond than by the laborious use of a fine needle impregnated with Diamond grit. The time consumed must have been very great. Yet do not these Diamonds engraved by the patience of Indian lapidaries virtually confirm to the hilt Pliny's statements?

Here, then, is the very beginning of industrial Diamond technology, which, as we shall see, grew mightily in volume especially in the 20th century.