His Majesty King Edward was presented with the great Cullinan diamond from the Transvaal in November 1907. This diamond weighs one pound and one-third (avoirdupois)—more than 21 oz. I have placed a good glass model of it in the Central Hall of the Natural History Museum; in the case with it is a glass model of another big diamond, the “Excelsior,” as now cut, and also models of the “Pitt” diamond, in the rough and in the cut condition. Diamonds lose enormously in the process of cutting. The Excelsior, like the Cullinan, is a Cape diamond of fine quality, and free from colour. It was the biggest diamond known until the giant Cullinan was found: in the rough it weighed 7 oz., or less than a third of the Cullinan. As now cut, it only weighs 1 3/4 oz. It is reduced to a quarter of its original size.

In the same way, the Pitt diamond, an Indian one, named after General Pitt, of Madras, weighed originally 3 oz., and is now (it is in Paris, in the Louvre, and is called “The Regent”) less than an ounce in weight. The biggest Indian diamond known—the Nizam—is not quite twice this size, whilst the Kohinoor, which is probably a fragment (a third) of the “Great Mogul”—a diamond which has disappeared, leaving only tradition and surmises as to its history—weighs no more than three-quarters of an ounce. This seems a small affair by the side of the twenty-one ounces of the Cullinan.

No one can guess what will happen to the Cullinan in cutting it. At the best, it may be reduced to something between four and five ounces in weight, and it may “fly” into fragments. It would be necessary deliberately to cut it up into smaller stones in order to obtain the full result of flashing of light and colour which twenty-one ounces of diamond can produce. And the operation of cutting and polishing is enormously expensive. One would have hoped that Sir William Crookes and other men of science would have been asked to examine this wonderful mass of transparent carbon by means of polarised light, RÖntgen rays, and radium, and to determine exactly its specific gravity before it was broken up. Indeed, it would probably have retained its greatest interest and value if never cut at all.

Glass or “paste,” as it is called, is made which cannot when new be distinguished from diamond by anyone but an expert, armed with the necessary tests. And the same is true as to paste imitations of all precious stones excepting the emerald (whose beautiful green tint cannot be exactly obtained), the cat’s-eye, which has a peculiar fibrous structure, and the opal. The real value and quality of precious stones, as compared with glass, depends on their durability, their hardness, their resistance to scratching, and “dulling” of face and edge. Even our Anglo-Saxon ancestors, as may be seen in the fine collection recently dug up at Ipswich by Miss Layard, and placed in the old house serving as the municipal museum there, made gems of glass and paste. In modern times the art of making artificial “precious stones” has reached a degree of perfection which, so far as decorative purposes are concerned, leaves the natural stones no claim to superiority.

Gigantic as the Cullinan diamond is, it represents only about half the daily output of the De Beers mines. By the end of 1904 ten tons of diamonds, valued at £60,000,000 sterling, had been removed from the Kimberley mines. It is difficult to imagine what has become of them all, and since they are, unlike paste, durable and permanent, how the demand for additions to those in use, keeps up. Twelve years ago about four million pounds was spent annually by the public on the purchase of diamonds. It is stated that the annual demand and expenditure are now even larger.

Diamond is a peculiar form or variety of the chemical element carbon—a very peculiar form most people will say who remember that charcoal and lamp-black are the common form of carbon. That one and the same unchangeable chemical element can exist as an amorphous black lump or powder, and also without addition or loss of chemical constituents, as the clearest, hardest, and most brilliant of crystals, is a paradox. The same strange capacity for existing in two totally different forms is exhibited by other fairly familiar elements. Sulphur is found in tertiary water-deposited clays in Sicily (it has nothing to do with Etna or Vesuvius) in the form of clear, lemon-coloured crystals half an inch or more in length. If you take some commercial stick-sulphur and melt it in a porcelain spoon, and pour half the melted stuff like treacle into a jar of water, you will find that it cools as translucent threads which are pliable and soft. The other half which you leave in the spoon to cool shoots out into the form of long brittle crystals of a needle-like shape. These two varieties of sulphur are nearly as different as lamp-black and diamond.

Diamonds are found at the Cape in a “blue ground” which is of volcanic origin, formed by the action of steam under enormous pressure. The blue volcanic mud has been thrust up from great depths in the earth’s surface in the form of “pipes” 100 yards to half a mile in diameter. It has long been known that at very high temperatures (4,000 deg. Centigrade) the metal iron dissolves carbon. The late Professor Moissan, of Paris, obtained artificial diamonds by suddenly cooling the iron in which carbon was dissolved by plunging the crucible into water. The outer shell of iron cools and forms a tightly closed shell enclosing the still liquid core. As this core cools it tends to expand, and thus produces an enormous pressure. The melted carbon cooling under this pressure assumes the crystalline colourless form known as diamond. There is good reason to believe that diamonds are formed, or have been formed, in association with metallic iron in a similar way, on a large scale, in great depths of the earth’s crust, and are shot up to the surface with other dÉbris in the volcanic steam mud which is the “blue ground.”

A few diamonds of small size have been found in the Ural Mountains, otherwise they are not natural products of the northern hemisphere. It is in India, Australia, South America, and South Africa that they are picked up, either in beds of streams, or in peculiar volcanic mud, or embedded in even harder rock. Many are in a condition of severe strain when found, and contain minute cavities filled with liquid carbonic acid. They are liable, in consequence, to break or even fly into powder when warmed by the hand or struck. Though usually colourless, diamonds may be yellow, green, blue, or red, and the rays of radium cause colourless diamonds to become coloured. Some diamonds, but not all, are phosphorescent—that is to say, like the well-known luminous paint—after exposure to strong light they acquire the power of shining themselves for a certain time when removed to a dark chamber. And the curious thing is that, though themselves colourless, some give out blue, some green, some yellow, and some red light. The most wonderful, however, in this respect are the rare diamonds which become luminous merely by rubbing, and leave phosphorescent streaks on the cloth with which they are rubbed. This property is similar to the phosphorescence shown by other kinds of crystals when heated or when simply fractured.

Diamonds are readily distinguished from paste by the RÖntgen rays, since they are transparent to those rays, whilst paste (or glass) is opaque to them. Radium also causes diamonds, but not paste, to phosphoresce. All diamonds are not equally hard, though they are the hardest of stones, and harder than steel, but not harder than the metal tantalum. Some Australian diamonds are known (from Inverel, New South Wales) which are so hard that at one time they could not be cut and polished; but only four years ago the rapidity of the wheels used in these processes was greatly increased, and these terribly hard diamonds were brought into subjection.

Thus it is clear that there are many extraordinary features of interest about the diamond, and that its brilliance and high price constitute only a small part of its fascination.