Diamonds

The Compound System

With gems like diamonds, where so large an intrinsic value is concentrated into so small a bulk, it is not surprising that robbery has to be guarded against in the most elaborate manner. The Illicit Diamond Buying (I.D.B.) laws are very stringent, and the searching, rendered easy by the “compounding” of the natives—which I shall describe presently—is of the most drastic character (Fig. 6). It is, in fact, very difficult for a native employee to steal diamonds; even were he to succeed, it would be almost impossible to dispose of them, as a potential buyer would prefer to secure the safe reward for detecting a theft rather than run the serious risk of doing convict work on the Cape Town Breakwater for a couple of years. I heard of a native who, secreting a diamond worth several hundreds of pounds, after trying unsuccessfully to sell it, handed it back to the manager of his compound, glad to get the sixpence a carat to which he was entitled. Before the passing of the “Diamond Trade Act” the value of diamonds stolen reached nearly one million sterling per annum.

A “compound” is a large enclosure about 20 acres in extent, surrounded by rows of one-story buildings of corrugated iron. These are divided into rooms holding each about twenty natives. A high iron fence is erected around the compound, 10 feet from the buildings. Within the enclosure is a store where the necessaries of life are supplied to the natives at a reduced price, wood and water being provided free of charge. In the middle is a large swimming-bath, with fresh water running through it. The rest of the space is devoted to recreation, games, dances, concerts, and any other amusement the native mind can desire. I have to thank the superintendents of the respective compounds, who spoke all the native dialects, for their kindness in showing us round, and suggesting dances and concerts, got up at ten minutes’ notice, for the benefit of my camera. The dancing was more of the character of attitudinising and marching to a monotonous tum-tum, the “orchestra” consisting of various-sized drums and what they call a piano—an octave or so of tuned slabs of wood held in order on stretched strings and struck with a wooden hammer. The native music as a rule is only marking time, but I have heard musical melodies accompanying some of their songs. In case of accident or illness there is a well-appointed hospital where the sick are tended. Medical supervision, nurses, and food are supplied free by the Company.

In the compound are to be seen representatives of nearly all the picked types of African tribes. Each tribe keeps to itself, and to go round the buildings skirting the compound is an admirable object-lesson in ethnology. At one point is a group of Zulus; next we come to Fingoes; then Basutos; beyond come Matabele, Bechuanas, Pondos, Shangains, Swazis, and other less-known tribes, either grouped or wandering around making friendly calls.

The clothing in the compound is diverse and original. Some of the men are evident dandies, whilst others think that in so hot a climate a bright-coloured handkerchief or “a pair of spectacles and a smile” is as great a compliance with the conventions of civilisation as can be expected.

The natives are not interfered with in their various amusements, always provided they do not make themselves objectionable to their neighbours. They soon learn that tribal animosities are to be left outside the compound. One Sunday afternoon my wife and I walked unattended about the compound, almost the only whites present among 1700 natives. The manners of the fold were so friendly, and their smiles so cordial, that the idea of fear vanished. At one part a Kafir was making a pair of trousers with a bright nickel-plated sewing-machine, in which he had invested his savings; next to him a “boy” was reading from the Testament in his own language to an attentive audience; in a corner a party were engaged in cooking a savoury mess in an iron pot; further on the orchestra was tuning up and Zulus were putting the finishing touches to their toilet of feathers and beads. One group was intently watching a mysterious game. It is played by two sides, with stones and grooves and hollows in the ground, and appears of most absorbing interest. It seems to be universal throughout Africa; it is met with among the ruins of Zimbabwe, and signs of it are recorded on old Egyptian monuments. I wanted to learn it, and an intelligent Zulu player offered to teach it to me in a few minutes. Captain Dallas, however, with a more accurate opinion of my intelligence than my friend the Zulu, assured me it would take months before I could begin to know anything about it. He had tried for years and could make nothing of it.

They get good wages, varying according to occupation. The work is appreciated, and there are always more applicants than can be accepted. On entering, the restrictions to which they must submit are fully explained, and they are required to sign for three months at least, during which time they must not leave the compound or mine. A covered way and tunnel lead the workers underground to the down shaft, while those working on the depositing floors go and come under guard. It is seldom that a man does not return once he has lived the life in the compound; some come again and again for years, only leaving occasionally to spend accumulated savings. The most careful men save money, and carry it at intervals to the superintendent to keep for them. Occasionally they ask to look at their savings, which may amount to £30 or £40, accumulated by driblets. They are ignorant of savings banks or interest, and are content if they see their own money in the original rags and papers. The Kafir, on demand, must behold his coins just as he handed them in, wrappings and all. Sometimes the superintendent will have as much as £1000 of savings in his care.

On leaving, the men generally draw all their savings, and it is not uncommon for a grateful Kafir to press £2 or £3 on Captain Dallas in recognition of his trouble. They are astonished when their offerings are declined; still more so when it is explained that if they would put their savings in a bank they would have a few extra pounds given to them for the privilege of taking care of it.

A shrewd young Pondo, who had been coming year after year, applied for some of his savings, and gave as a reason that he wanted to buy a wife. “But you said the same thing last year,” replied Captain Dallas; “I hope nothing has happened.” “No,” said the man; “one wife, she quarrel with me; two wives, they quarrel with each other; me peace!”

Underground Workings

In the face of constant developments I can only describe the system in use at the time of my own visits in 1896 and 1905. Shafts are sunk in the solid rock at a sufficient distance from the pipe to be safe against reef movements in the open mine. In 1903 the rock shafts in the De Beers and Kimberley Mines reached depths of 2076 and 2599 feet respectively. Tunnels are driven from these shafts at different levels, about 120 feet apart, to cross the mine from west to east. These tunnels are connected by two other tunnels running north and south, one near the west side of the mine and one midway between it and the east margin of the mine. From the east and west tunnels offsets are driven to the surrounding rock. When near the rock the offsets widen into galleries, these in turn being stoped on the sides until they meet, and upwards until they break through the blue ground. The fallen reef with which the upper part of the mine is filled sinks and partially fills the open space. The workmen then stand on the fallen reef and drill the blue ground overhead, and as the roof is blasted back the debris follows. When stoping between two tunnels the blue is stoped up to the debris about midway between the two tunnels. The upper levels are worked back in advance of the lower levels, and the works assume the shape of irregular terraces. The main levels are from 90 to 120 feet apart, with intermediate levels every 30 feet. Hoisting is done from only one level at a time through the same shaft. By this ingenious method every portion of blue ground is excavated and raised to the surface, the rubbish on the top gradually sinking and taking its place.

The scene below ground in the labyrinth of galleries is bewildering in its complexity, and very unlike the popular notion of a diamond mine (Fig. 7). All below is dirt, mud, grime; half-naked men, dark as mahogany, lithe as athletes, dripping with perspiration, are seen in every direction, hammering, picking, shovelling, wheeling the trucks to and fro, keeping up a weird chant which rises in force and rhythm when a greater task calls for excessive muscular strain. The whole scene is more suggestive of a coal mine than a diamond mine, and all this mighty organisation, this strenuous expenditure of energy, this costly machinery, this ceaseless toil of skilled and black labour, goes on day and night, just to win a few stones wherewith to deck my lady’s finger! All to gratify the vanity of woman! “And,” interposed a lady who heard this remark, “the depravity of man!”

The Depositing Floors

Owing to the refractory character of blue ground fresh from the mines, it has to be exposed to atmospheric influences before it will pulverise under the action of water and mechanical treatment.

From the surface-boxes, into which the blue ground is tipped when it reaches the top of the main shaft, it is transferred to side-tipping trucks and sent to the depositing floors by means of endless wire-rope haulage. The speed of the haulage varies from 2½ to 4 miles per hour. The trucks are counted automatically as they are sent to the floor by a reciprocating engine-counter placed on a frame near the tramline.

The depositing floors are prepared by removing the bush and grass from a fairly level piece of ground; this ground is then rolled smooth and hard. The floors extend over many square miles of country and are surrounded by 7-foot barbed wire fences, vigilantly guarded day and night. The De Beers floors, on Kenilworth, are laid off in rectangular sections 600 yards long and 200 yards wide, each section holding about 50,000 loads. The ground from the Kimberley Mine is the softest and only needs a few months’ exposure on the floors; the ground from De Beers is much harder and requires at least six months’ exposure, while some ground is so hard that it will not disintegrate by exposure to the weather under one or two years. The De Beers Mine contains a much larger quantity of this hard blue ground than the other mines, and in order to save the loss of time consequent on keeping an enormous stock of blue constantly on the floors, it has recently been decided to pass the harder and more refractory stuff direct from the mine through crushing mills.

For a time the blue ground remains on the floors without undergoing much alteration. But soon the heat of the sun and moisture produce a wonderful effect. Large pieces, hard as ordinary sandstone when taken from the mine, commence to crumble. At this stage the winning of the diamonds assumes more the nature of farming than mining. The ground is frequently harrowed and occasionally watered, to assist pulverisation by exposing the larger pieces to atmospheric influences. The length of time necessary for the ground to weather before it becomes sufficiently pulverised for washing depends on the season of the year and the amount of rain. The longer the ground remains exposed the better it is for washing.

It is curious to note that there is a marked difference in the rapidity of disintegration of the blue ground in each of the four mines. The longer the exposure, the more complete the pulverisation and the better for washing. Under normal conditions soft blue ground becomes sufficiently pulverised in from four to six months, but it is better to expose it for a longer period, even for a whole year.

Washing and Concentrating Machinery

After the blue ground has been weathered for a sufficient time, it is again loaded into trucks and hauled to the crushing machinery (Fig. 8). The first or “comet” crushers reduce the ground so that it will pass into hoppers and thence into revolving cylinders covered with perforated steel plates, having holes 1¼ inches in diameter which separate the finely crushed from the coarse pieces.

Pieces larger than 1¼ inches pass out of the end of the cylinders and fall upon a conveyor belt, which takes them to the end of the machine—these pieces are mostly waste rock which is found in the blue ground.

The fine ground which passes through the holes in the cylinder, together with a plentiful current of water, flows into the washing pans. These pans are of iron, 14 feet in diameter, furnished with ten arms each having six or seven teeth. The teeth are so set as to form a spiral, so that when the arms revolve the teeth carry the heavy deposit to the outer rim of the pan, while the lighter material passes towards the centre and is carried from the pan by the flow of water. The heavy deposit contains the diamonds. It remains on the bottom of the pan and near its outer rim. This deposit is drawn off every twelve hours by means of a broad slot in the bottom of the pan. The average quantity of blue ground passed through each pan is from 400 to 450 loads in ten hours. The deposit left in each pan after putting the above number of loads through amounts to three or four loads, which go to the pulsator for further concentration.

About 14 per cent of all the ground sent to the depositing floors is too hard to weather, so of late years crushing and concentrating plant has been erected to deal effectually with the hard lumps, thus saving the great lock-up of capital consequent on letting them lie on the floor a year or two.

The hard lumps being hauled to the upper part of the machine, are tipped into bins, whence they pass to crushing rollers which so reduce them that they will pass through a ring two inches in diameter. The coarse powder is screened through revolving cylinders having ½-inch and 1¼-inch perforations. The stuff passing through the finer holes goes to the finishing mill, while the coarser stuff goes to smaller crushers. Before the coarse lumps are re-crushed they pass over revolving picking tables, where any specially large diamonds are rescued, thus preventing the risk of breakage. From the picking tables the ground is scraped automatically into two sets of rolls, and the pulverised product screened again and graded into three sizes. The finest size, passing a ½-inch screen, goes to the washing pans, and the two coarser sizes to jigs. Large diamonds which have been separated from their envelope of blue are retained in the jig. The ground still holding the smaller diamonds passes out of the end of the jig and then through a series of rolls, screens, and jigs until the diamantiferous gravel is drawn from the bottom jigs into locked trucks running on tramways to the pulsator for further concentration and sorting.

The pulsator is an ingeniously designed but somewhat complicated machine for dealing with the diamantiferous gravel already reduced one hundred times from the blue ground, the pulsator still further concentrating it till the gravel is rich enough to enable the stones to be picked out by hand. The value of the diamonds in a load of original blue ground being about 30s., the gravel sent to the pulsator from the pans, reduced a hundredfold, is worth £150 a load. Stuff of this value must not be exposed to risk of peculation.

The locked trucks are hoisted by a cage to a platform, where they are unlocked and their contents fed into a shoot leading to a cylinder covered with steel sieving with holes from ¹/₁₆ to ⅝ of an inch in diameter. The five sizes which pass through the cylinder flow upon a combination of jigs, termed at the mines the pulsators. The bottoms of the jigs are covered with screens, or sieving, the meshes of which are a little larger than the holes in the revolving cylinder immediately at the back of them.

Over each screen is spread a layer of bullets to prevent the rich deposit from passing too rapidly through the screens. The jigs themselves are stationary, but from below an intermittent stream of water passes in rapid pulsations with an up and down movement. This pulsation keeps the diamantiferous gravel constantly moving—“alive” is the expressive word used—and tends to sort out the constituents roughly according to their specific gravity, the heavier particles working to the bottom and the lighter material washing off by the flow of water and passing into trucks, whence it is carried to the tailings heap. The heavier portions, by the up and down wash of the water, gradually work their way under the bullets and pass through the screens into pointed boxes, whence the heavy concentrates are drawn off upon endless belts. These convey their precious load to small elevators by means of which the concentrates are lifted into hoppers from which they are fed upon shaking tables.

CHAPTER IV

COLLECTING THE GEMS

The sorting room in the pulsator house is long, narrow, and well lighted (Fig. 9). Here the rich gravel is brought in wet, a sieveful at a time, and is dumped in a heap on tables covered with iron plates. The tables at one end take the coarsest lumps, next comes the gravel which passed the ⅜-inch holes, then the next in order, and so on. The first sorting is done by thoroughly trustworthy white men; for here the danger of robbery is greatest. Sweeping the heap of gravel to the right, the sorter scrapes a little of it to the centre of the table by means of a flat piece of sheet zinc. With this tool he rapidly passes in review the grains, seizes the diamonds and puts them into a little tin box in front of him. The stuff is then swept off to the left and another lot taken, and so on till the sieveful of gravel is exhausted, when another is brought in. The stuff the sorter has passed to his left as temporarily inspected is taken next to another part of the room, where it is again scrutinised by native convicts again and again, and whilst diamonds can be found in quantity sufficient to repay the cost of convict labour, it is passed under examination.

The diamond has a peculiar lustre, and on the sorter’s table it is impossible to mistake it for any other stone that may be present. It looks somewhat like clear pieces of gum arabic, with a sort of intrinsic lustre which makes a conspicuous shine among the other stones.

Automatic Diamond Collector

A series of experiments was initiated by Mr. Gardner Williams with the object of separating the diamonds from the heavy, valueless concentrates with which they are associated. An ordinary shaking or percussion table was constructed, and every known means of separation was tried without success. One of the employees of De Beers, Mr. Fred Kirsten, was in charge of the experimenting, under the supervision of the late Mr. George Labram, the manager of the large crushing plant, and afterwards mechanical engineer to the Company. Notwithstanding the fact that the specific gravity of the diamond (3·52) was less than that of several of the minerals associated with it, so that its separation would seem a simple matter, it was found in practice to be impossible owing to the slippery nature of the diamond. The heavy concentrates carried diamonds, and diamonds flowed away from the percussion table with the tailings. When it seemed that every resource to do away with hand-sorting had been exhausted, Kirsten asked to be allowed to try to catch the diamonds by placing a coat of thick grease on the surface of the percussion table with which the other experiments had been made. Kirsten had noticed that oily substances, such as axle grease and white or red lead, adhered to diamonds when they chanced to come into contact, and, he argued to himself, if these substances adhered to diamonds and not to the other minerals in the concentrates, why should not diamonds adhere to grease on the table and the other minerals flow away? In this way the remarkable discovery was made that diamonds alone of all minerals contained in the blue ground will adhere to grease, and that all others will flow away as tailings over the end of the percussion table with the water. After this was determined by thorough experiments, more suitable shaking tables were constructed at the Company’s workshops. These were from time to time improved upon, until now all the sorting (except for the very coarse size) is done by these machines, whose power of distinction is far superior to the keenest eye of the native.

Only about ⅓ of 1 per cent of diamonds is lost by the first table, and these are recovered almost to a stone when the concentrates are passed over the second table. The discrimination of this sorter is truly marvellous. Native workers, although experienced in the handling of diamonds, often pick out small crystals of zircon, or Dutch boart, by mistake, but the senseless machine is practically unerring.

The grease containing the diamonds, together with a small percentage of very heavy minerals, such as iron pyrites and barytes, is scraped from the tables, placed in buckets made of steel plates with fine perforations, and boiled or steamed. The grease passes away to tanks of water, where it is cooled and is again fit for use. The diamonds, together with small bits of iron pyrites, brass nails from the miners’ boots, pieces of copper from the detonator used in blasting, which remain on the tables owing to their high specific gravity, and a very small admixture of worthless deposit which has become mechanically mixed with the grease, are then boiled in a solution containing caustic soda, where they are freed from all grease. The quantity of deposit from the size of ⅝ of an inch downwards, which now reaches the sorting table, does not exceed 1 cubic foot for every 12,000 loads (192,000 cubic feet) of blue ground washed. As already stated, ⁵/₁₂ of 1 per cent of the whole mass of blue formerly passed to the sorting tables; or, from 12,000 loads, which is about the daily average of the quantity washed at De Beers and Kimberley Mines, 800 cubic feet had to be assorted by hand.

The Yield of Diamonds

Sometimes as many as 8000 carats of diamonds come from the pulsator in one day, representing about £20,000 in value.

When the bare statement is made that nearly 5,000,000 truck-loads, or more than 4,000,000 tons of blue ground, have been washed in a year, the mind only faintly conceives the prodigious size of the mass that is annually drawn from the old craters and laboriously washed and sorted for the sake of a few bucketfuls of diamonds. It would form a cube of more than 430 feet, or a block larger than any cathedral in the world, and overtopping the spire of St. Paul’s, while a box with sides measuring 2 feet 9 inches would hold the gems. From two to three million carats of diamonds are turned out of the De Beers mines in a year, and as 5,000,000 carats go to the ton, this represents half a ton of diamonds. To the end of 1892 10 tons of diamonds had come from this mine, valued at £60,000,000 sterling. This mass of blazing diamonds could be accommodated in a box 5 feet square and 6 feet high.

The diamond is a luxury, and there is only a limited demand for it throughout the world. From four to four and a half millions sterling is as much as is spent annually in diamonds; if the production is not regulated by the demand, there will be over-production, and the trade will suffer. By regulating the output the directors have succeeded in maintaining prices since the consolidation in 1888.

The blue ground varies in its yield of diamonds in different mines, but is pretty constant in the same mine. In 1890 the yield per load of blue ground was:

Varieties of Diamonds
Fancy Stones

Diamonds occur in all shades, from deep yellow to pure white and jet black, from deep brown to light cinnamon, also green, blue, pink, yellow, orange, and opaque.

Both in Kimberley and De Beers the blue ground on the west side is poorer in diamonds than the blue ground in other parts of the mines. The diamonds from the west side also differ somewhat from those in other parts of the same mine.

The diamonds from each mine have a distinctive character, and so uniform are the characteristics that an experienced buyer can tell at once the locality of any particular parcel of stones. An isolated stone may, of course, be found occasionally in any one mine which is characteristic of some other source of production, but this is the exception to the general rule.

There is a great similarity between the produce of the De Beers and Kimberley mines. A day’s wash from either of these mines could be distinguished from each other, but not so easily the majority of the individual stones.

The Kimberley Mine produces a small percentage of white crystals, octahedral in shape, is noted for its large macles, and, in common with the De Beers Mine, it also yields a large percentage of coloured and large yellow diamonds.

The De Beers Mine produces a comparatively small percentage of really white diamonds, but is noted for its fine silvery capes.

The Dutoitspan Mine is noted for its fine white cleavages, silver capes, large yellows, and an exceptional proportion of large stones generally. It also produces a small proportion of fine white, octahedral-shaped crystals and a comparatively small proportion of diamonds below 0·2 of a carat in size.

The Bultfontein Mine produces a very large percentage of white diamonds, mostly octahedral in shape and generally small in size. It produces very few coloured stones, but a larger percentage of flawed and spotted stones than any other mine. Even the apparently pure stones from this mine frequently develop flaws in cutting, which in the rough were imperceptible to the naked eye.

The Wesselton Mine diamonds are noted for an abnormally large percentage of octahedral stones, a large proportion of which are free from flaws. White and brown stones predominate in this mine; there is almost an entire absence of the ordinary yellow, but very fine golden-coloured fancy stones are unearthed occasionally, invariably in the form of cleavage, and hardly ever exceeding 2 carats each in weight.

For “golden fancies” this mine is unrivalled. Wesselton diamonds are easily distinguished from the produce of every other mine by a decided gloss common to them.

Wesselton produces more stones of 10 carats each and over than Bultfontein, but comparatively few large stones of over 50 carats each. It produces a very large percentage of small diamonds under 0·2 of a carat. With Bultfontein it shares the distinction of yielding cubical stones occasionally. It also produces a small percentage of blue-whites.

The Frank Smith Mine produces very fine white diamonds, fairly regular in shape, mostly octahedral, and hardly any coloured stones. Many of the stones are grooved at the edges.

The Kamfersdam Mine yields diamonds of very inferior quality, dark brown being the predominating colour, and even the majority of the better-class stones from this mine are faintly tinged with brown.

The Kimberley West, formerly known as Theron’s Mine, situated about 30 miles due west of Kimberley, yields a very small percentage of blue-whites, fine “silver capes,” and a large proportion of brown diamonds, somewhat better in quality than Kamfersdam and more regular in shape. The diamonds from this mine present a distinctly “alluvial” appearance, but they are nevertheless distinctive in character from river diamonds and much inferior in quality.

The diamonds from the Leicester Mine are of a distinctive character; they are very much grooved, extremely bad shapes for cutting, and many of the stones are cross-grained.

The Newlands Mine, West Griqualand, about 40 miles north-west of Kimberley, is interesting on account of the occurrence of diamond in what the Reverend Professor Bonney considers to be its true matrix. The workmen occasionally come across well-rounded, boulder-like masses of eclogite, a rather coarsely crystalline rock, sometimes more than a foot in diameter. Some of these boulders have diamonds imbedded in them. One piece examined by Professor Bonney measured approximately 4 inches by 3 inches by 2 inches, and appeared to have been broken off a larger eclogite boulder. In it were seen ten diamonds, mostly well-crystallised octahedra, perfectly colourless, with brilliant lustre, four of them being comprised within a space of a quarter of an inch square. All these diamonds were on the surface. Probably others would have been found inside, but it was not considered desirable to destroy the specimen by breaking it up. It is now in the Natural History Museum, having been presented by the Directors of the Newlands Mine.

Eclogite has been found in other diamond mines, but I am not aware that diamonds have been found imbedded in it except in the Newlands Mine.

Stones from Jagersfontein, in the Orange River Colony, display great purity of colour and brilliancy, and they have the so-called “steely” lustre characteristic of old Indian gems.

Falling off of Yield with Depth

According to tables furnished by the De Beers Company, the yield of the De Beers and Kimberley mines has declined as the depth increases. At the same time the value of the stones has risen, and diamonds are more expensive to-day than at any previous time.

Stones other than Diamonds

Accompanying diamonds in the concentrates are a number of other minerals of high specific gravity, and some of notable beauty. Among these are the rich red pyrope (garnet), sp. gr. 3·7, containing from 1·4 to 3 per cent of oxide of chromium; zircon, in flesh-coloured grains and crystals, sp. gr. 4 to 4·7; kyanite, sp. gr. 3·45 to 3·7, discernible by its blue colour and perfect cleavage; chrome diopside, sp. gr. 3·23 to 3·5, of a bright green colour; bronzite, sp. gr. 3·1 to 3·3; magnetite, sp. gr. 4·9 to 5·2; mixed chrome and titanium iron ore, sp. gr. 4·4 to 4·9, containing from 13 to 61 per cent of oxide of chromium, and from 3 to 68 per cent of titanic acid, in, changeable quantities; hornblende, sp. gr. 2·9 to 3·4; barytes, sp. gr. 4·3 to 4·7; and mica. Some of the garnets are of fine quality, and one was recently cut which resembled a pigeonblood ruby, and attracted an offer of £25.

In the pulsator and sorting house most of the native labourers are long-sentence convicts, supplied with food, clothing, and medical attendance by the Company. They are necessarily well guarded. I myself saw about 1000 convicts at work. I was told that insubordination is very rare; apart from the hopelessness of a successful rising, there is little inducement to revolt; the lot of these diamond workers is preferable to life in the Government prisons, and they seem contented.

CHAPTER V

THE DIAMOND OFFICE

From the pulsator the diamonds are sent to the general office in Kimberley to be cleansed in a boiling mixture of nitric and sulphuric acids. A parcel of diamonds loses about half a part per 1000 by this treatment. On one of my visits to the diamond office the door opened and in walked two young men, each carrying a large enamelled saucepan containing something steaming hot. They went to one of the zinc-covered tables and turned out from the saucepans a lustrous heap of 25,000 carats of diamonds (Fig. 10). They had just been boiled in acid and washed.

After purification the diamonds are handed to the valuators (Fig. 11), who sort them into classes, according to size, colour, and purity. In the diamond office they are sorted into ten classes. In the year 1895, in 1141·8 carats of stones, the proportions of the different classes were as follows:

It is a sight for Aladdin to see the valuators at work in the strong-room of the De Beers Company at Kimberley. The tables are literally heaped with stones won from the rough blue ground—stones of all sizes, purified, flashing, and of inestimable price; stones that will be coveted by men and women all the world over; and last, but not least, stones that are probably destined to largely influence the development and history of a whole huge continent.

CHAPTER VI

NOTEWORTHY DIAMONDS

Prodigious diamonds are not so uncommon as is generally supposed. Diamonds weighing over an ounce (151·5 carats) are not unfrequent at Kimberley. Some years ago, in one parcel of stones, I saw eight perfect ounce crystals, and one stone weighing 2 ounces (Fig. 12). The largest diamond from the Kimberley mines weighed 428½ carats, or nearly 4 ounces troy. It measured 1⅞ inch through the longest axis and was 1½ inch square. After cutting it weighed 228½ carats, losing 200 carats in the process. The largest known diamond was discovered in January, 1905, at the New Premier Mine, near Pretoria. This mine is of the same type as the Kimberley mines, but larger in size, and, in fact, is the largest known diamantiferous pipe in the world—the pipe containing the “blue ground,” along the longer diameter of its oval-shaped cross-section, measuring over half a mile, and its area is estimated at 350,000 square yards. This pipe breaks through felsitic rocks. The diamond, called “Cullinan” from the name of one of the directors of the company on whose farm it was discovered, was presented to King Edward on his birthday by the people of the Transvaal. It weighed no less than 3025¾ carats, or 9586·5 grains (1·37 lb. avoirdupois). It was a fragment, probably less than half, of a distorted octahedral crystal; the other portions still await discovery by some fortunate miner. The frontispiece shows this diamond in its natural size, from a photograph taken by myself. I had an opportunity of examining and experimenting with this unequalled stone before it was cut. A beam of polarised light passed in any direction through the stone, and then through an analyser, revealed colours in all cases, appearing brightest when the light passed along the greatest diameter—about 4 inches. Here the colours were very fine, but no regular figure was to be seen. Round a small black spot in the interior of the stone the colours were very vivid, changing and rotating round the spot as the analyser was turned. These observations indicated internal strain.

The clearness throughout was remarkable, the stone being absolutely limpid like water, with the exception of a few flaws, dark graphitic spots, and coloured patches close to the outside. At one part near the surface there was an internal crack, showing well the colours of thin plates. At another point there was a milky, opaque mass, of a brown colour, with pieces of what looked like iron oxide. There were four cleavage planes of great smoothness and regularity. On other parts of the surface the crystalline structure was very marked. The edges were rounded in parts, and triangular markings (depressions) were to be seen. I also noticed square depressions, nearly as sharp and perfect as the triangular ones.

The cleaving and cutting and polishing of the Cullinan diamond was entrusted to the firm of Asscher and Co., in Amsterdam. The cleavage of the diamond was very successfully accomplished by Mr. Joseph Asscher. An incision half an inch deep was made with a sharp diamond point in the proper place, then a specially designed knife blade was placed in the incision and it was struck a heavy blow with a piece of steel. The diamond split through a defective spot, part of which was left in each portion of the diamond.

Gigantic as is the Cullinan diamond, it represents in weight less than half the daily output of the De Beers mines, which averages about 7000 carats per day.

Next in size to the Cullinan comes the one which was found at the Jagersfontein Mine. It weighed 970 carats—over half a pound.

The following table gives the names and weights of some historic diamonds (Fig. 13):

  1. Koh-i-noor, after the second cutting, 106 carats.
  2. Loterie d’Angleterre, 49 carats.
  3. Nizam of Hyderabad, 279 carats.
  4. Orloff, 194 carats.
  5. Koh-i-noor, after first cutting, 279 carats.
  6. Regent or Pitt, 137 carats.
  7. Duke of Tuscany, 133 carats.
  8. Star of the South, 124 carats.
  9. Pole Star, 40 carats.
10. Tiffany, yellow, 125 carats.
11. Hope, blue diamond, 44 carats.
12. Sancy, 53 carats.
13. Empress Eugenie, 51 carats.
14. Shah, 86 carats.
15. Nassak, 79 carats.
16. Pasha of Egypt, 40 carats.
17. Cullinan, 3025 carats.
18. Excelsior, Jagersfontein, 969 carats.