Diamonds and Precious Stones – Louis Dieulefait


PART IX.   False Precious Stones.

Under the name of false precious stones, there arc two kinds of productions which are essentially different—the one natural, the other artificial. The first comprehends stones sufficiently hard to resist the file; they are generally quartz, either hyaline or variously coloured. The second consists of artificial compositions of the nature of glass.

There is an intermediate order, the productions belonging to which, if well executed, are especially calculated to deceive, and are used to great extent in the East Indies. They are called semi-stones, or doublets. It is of some importance to examine this subject, because there is a prevalent belief that all false stones necessarily have glass as their base, and are consequently of little hardness. People often say, when their rubies or their topazes are declared false, ” But, see, here is a file; try to scratch these stones; you will not succeed.” Very true; but submit any piece of quartz to the same test, and the result will be the same.

Since, as we have said, hyaline or variously coloured quartz is very abundant in nature, it is easy to procure, at insignificant prices, stones that perfectly resist the file, and show, often in a remarkable manner, the whole series of colours that we admire in real precious stones.

Stones of this kind are very abundant in commerce; it might be said that, with few exceptions, all those designated as occidental are of this character, and possess consequently hardly any value. Another deception of the same kind consists in passing off a stone of a certain nature and a certain value, for another stone of a different nature and a much higher value.

The colourless varieties of sapphire and topaz, which in density, in hardness, and in refractive power differ but little from the diamond, are frequently cut into roses and brilliants, and sold for diamonds. A proof of this fact is furnished by the commercial price of the colourless topaz, which is much greater than it could obtain as topaz. It is valued in the secret hope that after cutting it may be sold for diamonds.

At the present day there are means—such as the scales for determining specific gravity, polariscopes, &c.—for distinguishing with mathematical certainty the diamond from the sapphire or topaz; but these tests are of modern origin; and in the middle ages not only colourless topazes, but those whose tint had been removed in different ways, principally by the action of fire, frequently passed current for diamonds.

Nay more than this, under the influence of the ideas that then prevailed concerning transmutation, the successful experimenters believed that they had actually transformed rubies and topazes into diamonds.

Cardan furnishes some very curious details on this subject. He gives a receipt by which ” a limpid sapphire of a faint colour” may be boiled in melted gold and converted into a true diamond.


This mode of imitating real stones, though varying in a great many respects, is generally effected by giving the proper shape to a morsel of strass; removing from the upper portion of it a certain thickness, and replacing this by hard stone in such a way as to complete exactly the strass stone, then mounting the whole in a setting that completely conceals the line of junction of the two stones.

Doublets are of two kinds: in both the under part is strass, but in one the upper part is a plate of the real stone; in the other, it is simply hard stone, generally quartz, and of no value.  The invention of this process has been attributed to a modern jeweller of Paris, named Bourguignon; but in reality it can be traced as far back as the fifteenth century.

A complete description of the mode of manufacturing doublets is given by Cardan, who has even preserved for us the name of the inventor:— “A fraud of a very bad character, and one very difficult to find out, was employed by Zocolino.

This venerable personage used to take a thin fake of real precious stone, such as carbuncle, emerald, &c, when he wished to imitate the carbuncle or emerald, choosing such pieces as had but little colour, and were consequently very cheap. Underneath he placed a piece of crystal sufficiently thick, and united the two parts by means of a transparent glue, in which he incorporated a colouring matter in harmony with the stone that he meant to imitate—brilliant red for carbuncle, green for emerald,  &c.

He concealed the line of junction of the two parts by means of the setting; and to avoid giving rise to suspicion, he set them in gold, which was not allowed except in the case of real precious stones. “In this way this magnificent workman deceived everybody, even the lapidaries.

However, the fraud was at last discovered, and Zocolino took refuge in flight. ” It appears that this personage had a peculiar disposition for fraud, for he turned his attention afterwards to the fabrication of counterfeit money; and ended by being condemned to death.”

An examination of the objects adorned with precious stones, that have been executed in the middle ages, shows that the process described by Cardan was not unfrequently employed.


The basis of all false stones of this kind is glass. A fixed alkali (soda or potash) and silica heated to a red heat will combine and produce glass. Alumina, lime, magnesia, &c, may enter into the combination with the silica; but the result in both cases is colourless, or what is ordinarily called white glass. But if to these substances metallic oxides, or metals in a divided state, are added, even in minute quantities, the result is coloured glass.

Chemical analysis shows us that the elements of glass are found in all vegetables. If, then, a fire consumes a certain quantity of wood, gathered together at a single spot, vitrifications will be found in the residuum. When silicious stones are subjected to an intense heat, the bases contained in the stones and in the cinders combine and produce glass.

This is what may be seen every day in an examination of the interior walls of a lime-kiln or brick-kiln. It is evident, then, that the discovery of glass belongs to the earliest period of man’s existence. If it be remarked, besides, that the glass thus obtained is always coloured, and therefore in harmony with the pronounced taste of primitive people for brilliant objects, we understand how these vitreous substances produced by conflagrations and, above all, by the action of fire upon silicious stones, must have excited, in the most lively manner, the attention of men from the first ages of our species.

Had this book been written a dozen or fifteen years ago, it could have furnished but little information on this head; but, thanks to the researches of archaeologists, and in particular those of M. Boucher de Perthes—-for whom, no doubt, history reserves an exceptional place in its annals—humanity beholds its origin almost instantaneously extended far beyond the historic ages, far beyond all traditions!

A new period, during which man lived upon our globe, and which has not until our own epoch been suspected, is now revealed in the most incontestable manner; and among the remains of human industry referable to that remote epoch, are found objects of coloured glass. It must be remarked that coloured glass is much more easily obtained than glass without colour, and that the latter has been produced with ease only in quite modern times.

Without departing from historic times, but only reverting to their most ancient ages, we find that the Egyptians understood very early the manufacture of glass, and especially the coloured glasses. The design of an Egyptian vase of blue glass, ornamented with white and yellow, is given in Fig. 92. In quality of material, in form, in elegance of ornamentation and harmony of colouring, this vase is in no respect inferior to the best productions of the present day, and yet it must have issued from the hands of the Egyptian workman four thousand years ago.

In Figs. 91, 93, 94, 95, and 96, the objects represented are of ceramic paste. From an artistic point of view, these objects are of no value, but the delicacy of their details is well worth notice, especially when we consider that they must have been moulded when the matter was in a soft state.

In the time of Pliny, the manufacture of false stones was far advanced as a branch of industry among the Romans. There existed several treatises upon the subject; and Pliny declared that it was a difficult task to distinguish between the false and the true. Not only in Rome were false stones in vogue, but, according to Pliny, the Indians counterfeited jewels with success, especially opals.

The processes that Pliny was so careful not to divulge, were not held sacred with the same scrupulousness by the alchemists of the twelfth and thirteenth centuries. Both Albertus Magnus and St. Thomas Aquinas refer openly to this subject; and the latter in his treatise on the Essence of Minerals, states explicitly that there were “men who fabricated artificial jewels.”

Among the precious stones counterfeited, he instances the hyacinth, sapphire, emerald, ruby, and topaz. At the commencement of the Renaissance the fabrication of false stones still continued; but it was not yet separated from much hesitation and experiment. Cardan proves this in his curious receipts.

A century later we perceive by the descriptions of Kircher that the industry had greatly advanced. To the unburned “brick” of Cardan, in whose cavity his mixture for precious stones was heated, excellent crucibles had succeeded; special furnaces had replaced the brick-kiln; and in the time of Kircher, that is to say, about the middle of the seventeenth century, false stones were no longer manufactured according to methods differing for each stone, but according to a general formula much the same as that followed at the present day.

No other proof is needed than the writings of Kircher to dissipate the error that has ascribed the invention of strass—a peculiar kind of glass of considerable refractive power, which forms the base of all modern artificial gems—to a workman of that name, towards the close of the last century. This production was perfectly well known in the middle ages; and it was used for exactly the same purposes as it is used for to-day—for decoration, and the counterfeiting of precious stones. It is distinguished from ordinary glass by the presence of about 50 per cent, of oxide of lead among its constituents.