Diamonds are generally cut either as rose diamonds or as brilliants. The rose diamond is flat beneath, while the upper face rises into a dome, and is cut into facets. The brilliant, which is always three times as thick as the rose diamond, is likewise cut into facets, but so as to form two pyramids rising from a common central base or girdle. Each pyramid is truncated at the top by a section parallel to the girdle, which cuts off 5⁄18 of the whole height from the upper one, and 1⁄18 from the lower one. The superior and larger plane thus produced is called the table; and the inferior and smaller one is called the collet. Although the rose diamond projects bright beams of light in more extensive proportion often than the brilliant, yet the latter shows an incomparably greater play, from the difference of its cutting. In executing this there are formed thirty-two faces of different figures, and inclined at different angles all round the table on the upper side of the stone, while on the under side twenty-four other faces are made round the small table. It is essential that the faces of the top and the bottom shall correspond together in sufficiently exact proportions to multiply the reflections and refractions, so as to produce the gorgeous display of prismatic colours which renders the brilliant so pre-eminently beautiful.
From the hardness of the diamond, its cutting is a very tedious and expensive operation, requiring more time in the proportion of fifty to one than the cutting of the sapphire, which comes next to it in hardness.
Experiment has determined that the diamond consists of pure carbon, so that the same substance which in its common black state is utterly worthless in very small quantities, becomes the most costly of precious stones, when it makes its appearance in the crystalline form. Already Newton, by observing the extraordinary refractive power of the diamond, had been led to place it among combustibles; but Cosmo III., Grand Duke of Tuscany, was the first who proved the truth of this bold conjecture by actual observation. He exposed diamonds to the heat of the powerful burning glass of Tschîrnhausen, and saw them vanish in a few moments into air. The formation of the diamond in nature is one of the many problems which ‘our philosophy’ has not yet enabled us to solve. Time is an element which enters largely into nature’s works; she occupies a thousand or even thousands of years to produce a result, while man in his experiments is confined to a few years at most.
The most anciently renowned diamond districts are situated in the Indian peninsula, in the kingdoms of Golconda and Visapour, extending from Cape Comorin to Bengal, at the foot of a chain of mountains called the Orixa, which appear to belong to the trap-rock formation. Tavernier describes them as giving employment to thousands of workmen, but they seem now to be all but exhausted.
We are but little acquainted with the diamond mines of Landak in Borneo, though Ida Pfeiffer, on her second voyage round the world, obtained permission to visit them, a favour but rarely accorded to strangers by the suspicious potentate to whom they belong. So much is certain, that very few stones from this quarter find their way to the civilised world, which at present draws its chief supplies from the mines of Serro do Frio and Sincora in Brazil.
When diamonds were first found in the Serro do Frio, about the beginning of the last century, the real value of the glittering crystals was so little known that they were made use of as card-marks by the planters of the neighbourhood. An inspector of mines, who had been some time in India, was the first who discovered their true nature. Wisely keeping his secret to himself, he collected a large quantity of them, and escaped with his treasure to Europe. In 1729, the governor of Brazil, Don Lourenço de Almeida, sent some of the transparent stones of the Serro to the court of Lisbon with the remark that he supposed them to be diamonds, and thus the attention of Government was at length attracted to their value. By a decree of the 8th of February, 1730, the diamond district was placed under the rule of an Intendant, armed with the most arbitrary powers. Not only all strangers were carefully excluded from its limits, but not even a Portuguese or a Brazilian was allowed to tread its forbidden ground without a special permission; its population was limited to a scanty number, nor durst the foundation of a new house be laid unless in the presence of magistrates and mining inspectors. A system of secret delations was introduced worthy of the worst times of the Inquisition, and many an innocent person was banished, imprisoned, or transported to Africa, without even knowing his accuser, or the trespass laid to his charge. In one word despotism seemed to have exhausted all her inventive powers for the purpose of securing to the Crown the monopoly of the costliest gem on earth.
But in spite of every precaution, it was impossible to put down the contraband trade in diamonds. The audacity of the smugglers increased with the obstacles placed in their way, so that a far more considerable quantity of diamonds was secretly sold and exported than ever came into the hands of Government. Traversing the deep forests on almost inaccessible mountain paths, the bold free-traders met, at some place of appointment, the negroes who had been able to secrete some of the precious stones, and paid them a trifle for diamonds which beyond the limits of the district were worth at least twenty times the price given. Sometimes even the smugglers searched for diamonds themselves in the unfrequented wilderness. While some were washing the sands, others kept watch upon an eminence, and gave notice of the approach of the soldiers, who were constantly patrolling the district.
The heaviest penalties could not prevent the inhabitants of the Serra from defrauding the Crown, and Herr von Tschudi (‘Travels in South America in 1857–1861’) was told many amusing instances of their smuggling contrivances. One of them had concealed a diamond of twenty-five carats in the handle of his riding whip, for which purpose he had practised for many weeks the art of plaiting the thin leather straps which covered it, and another had secreted his precious stones in a kettle with a double bottom.
When the Brazils became an independent country, the monopoly of the diamond trade was abandoned by the new Government, and any speculator was allowed to search for diamonds on payment of a slight duty. The precious stones are found chiefly in alluvial deposits (Cascalho virgem), in the beds of torrents, or along low river-banks, and frequently large quantities of overlying rubbish. (Cascalho bravo) have to be removed before the diamond-bed can be reached. The mining labours are generally performed by slaves, though some of the poorer miners, or Faiscadores, have no other assistance but that of their own families. The work varies with the seasons. During the dry period of the year the cascalho is removed from the beds of the desiccated brooks, and dams are raised or canals dug for the purpose of turning off the stream into another channel, while the wet season is made use of for washing the sands. While this operation is going on, an overseer, seated on a high chair, keeps a sharp look-out upon the negroes; but in spite of all his attention, and of the severe punishments that await them in case of discovery, they know how to secrete many a diamond, by rapidly throwing it into their mouth, and concealing it under their tongue or swallowing it. In the Portuguese times an Intendant, complaining to the overseers of the frequency of theft, accused them of negligence, but was told that no vigilance in the world could prevent it. To convince himself of the fact, he ordered a negro who enjoyed the reputation of being a most expert hand at secreting diamonds to be brought before him, and placing a small stone in a heap of sand, promised him his liberty in case he should succeed in appropriating the stone without being detected. The negro began to wash the sand according to the usual method, while the Intendant was observing him all the time with the eyes of a lynx. After a few minutes he asked the slave whether he had found the stone. ‘If the word of a white man can be trusted,’ answered the black, ‘I am from this moment free;’ and taking the diamond out of his mouth, he handed it to the Intendant.
The negroes employed in the diamond washings are generally hired by the miners at so many milrees a week. Although their labour is very severe, they generally prefer it to any other, as on Sundays and Feast-days they are allowed to search on their own account (of course in places not previously occupied), and have, moreover, an opportunity of stealing diamonds.