Pick from the Past
Natural History, May-June 1921


The tools of the diamond lapidary’s art are very simple. The little metal cup or “dop,” in which the diamond is being placed, as well as the wooden holder which carries it, are of exactly the same shape as those used by the diamond cutters of a hundred years ago.

How Diamonds
Are Polished

SUPPOSE you were taking a walk somewhere in the middle of South Africa and, happening to glance down, saw at your feet a small, angular, irregular object, clear like glass but with a surface that looked as though it had been smeared with oil. You would probably kick it aside and proceed on your way; and yet this insignificant-looking thing might easily be a diamond of great value.

Diamonds as they are found in the rough state are not impressive. They have none of the magical flashes of light which in the finished stone make them unique among the noble family of gems. It is in polishing that a goodly part of the price of a diamond is acquired; for the art of turning a rough diamond into a glittering brilliant is a long process requiring a superlative degree of skill. There is no better way to appreciate this than to follow the diamond from the mine to the jeweler and see for ourselves just what happens to it.

When the diamonds are taken out of the mine, not by any means are all of them clear and colorless, as a self-respecting diamond should be; indeed only about 25 per cent of the stones found are without some faint color. Of the remainder about one third are of a light shade of color, such as violet, yellow, or brown, and are known as “off-color” stones. The remainder, roughly one half of the total find, are more or less deeply colored and are consequently of no value for jewelry although still usable for diamond cutting and polishing or for facings for rock drills. So we find that at the beginning of its travels the diamond is introduced to the sorter. The sorter is a kind of super-expert on diamonds whose eye has been trained through years of practice to detect the slightest variations in the color of diamonds and to find flaws in the stones with an ease which is little less than uncanny. Safeguarded behind a heavy metal screen, the diamond appraiser sits with a pile of rough stones before him, judging each stone and assigning it to its proper heap.

The first consideration in sorting diamonds is the adaptability of the stone for cutting. Let us assume that the stone whose travels we are following is sorted into the grade known as “close goods,” comprising complete, flawless crystals from which fair-sized brilliants can be cut or, to use the trade term, “made.” These usually have eight sides or faces, triangular in shape. Next comes a resorting of the “close goods” into eight grades, ranging from blue-white, which comprises the stones of finest quality, to yellow and brown, which are so badly off-color as to be unfit for gems.


Like a skilled surgeon the diamond lapidary performs the delicate operation which is known as “slitting.” Just the right amount of the stone, no more and no less, must be split away. The intent expression on the face of the operator bears witness to the momentous effect of the slight blow he is about to strike on the steel knife edge which he holds in his left hand.
If our stone has passed the critical test of the sorter and has been placed in one of the higher grades, it is weighed, wrapped up in a parcel with others of its kind, a price per carat is assigned to it, and it is sold to a diamond dealer, and ultimately finds its way to the workshop of the diamond polisher. Here, at the hands of a highly skilled workman, it is destined to he turned into a gem fit to grace beauty or proclaim opulence.

Most of this work is done in Holland, and especially in Amsterdam, which since the fifteenth century has been famous for this industry, in reality an art, but there are, nevertheless, a number of shops in operation right here in our city of New York. Like many other operators who depend for their success on a high degree of manual skill the diamond cutter has few tools, and these are relatively primitive and have changed little since the days of Louis de Bequem, who cut diamonds in 1475. The lapidary depends like the violin player on the delicacy of his touch, and like the painter on the accuracy of his eye, and he scorns to use complex mechanical devices to aid him in his difficult task.

The surface irregularities, together with any superficial flaws or dark patches, are first split away from the stone, which breaks naturally along smooth, even surfaces parallel to the natural faces of the crystal. To accomplish this our diamond is firmly cemented to the end of a wooden stick which in turn is made fast in an upright position, and thereupon with the sharp corner of a diamond fragment a deep scratch is made in the surface of the stone. A knife edge is then held in the right position on the scratch, and a sharp blow with a light tool on the back of the knife edge suffices to remove the undesirable flake, leaving the surface bright and very smooth. Sometimes, when the stone is large, it is of advantage to saw it into two or more pieces so as to save as much as possible of the weight in cut diamonds. This is accomplished with a thin disk of bronze, about four inches in diameter, revolving very rapidly and having its edge charged with diamond dust at the beginning of the sawing. As the saw bites into the stone, it keeps recharging itself with the diamond sawdust. It takes many hours for this little “buzz saw” to eat its way through half an inch of diamond, but the finished product is so valuable that a day or so of labor makes little impression on the cost sheet.

The rough shaping of the diamond is done through an operation called “bruting,” which consists of wearing away the corners by rubbing one stone against another. Formerly this was a strictly manual process, the two diamonds being mounted on sticks held in either hand by the lapidary. Even into the ancient and conservative art of diamond cutting, however, some mechanical improvements have made their way, and now in most of the shops a rapidly twirling spindle takes the place of one of the hand sticks. The remaining stick has grown in length to suit the modern method. It is now about two feet long and can be firmly grasped with both hands and held in a rest so that the diamond it bears at its end can be rubbed against its fellow, which is spinning around in front of it.

Having rough-shaped our diamond we now come to the finishing operation, the producing of the facets which give brilliancy and sparkle to it, an operation which is technically known as polishing. The holder of the stone during the polishing consists of a small metal cup on a long stem, which is called a “dop” and much resembles a tulip, which famous Dutch flower may have suggested its shape. A solder composed of one part tin and three parts lead is placed in the dop and heated until soft.


Even the refuse from this operation is valuable and must be saved. As the lapidary rough-shapes his diamonds, rubbing or “bruting” the one on the end of the long stick which he holds under his right arm, against the other on the rapidly turning spindle which is driven by the belt, the dust and fine fragments fall into the little box shown in the centre of the picture. Only the protruding end of the stick is visible in the illustration.
The diamond is then embedded in the solder with the portion of the stone on which the desired facet is to be cut placed uppermost and almost completely surrounded by the solder. When the diamond has been properly adjusted in the dop, it is plunged in cold water to cool and harden the solder. Such drastic treatment would cause less aristocratic stones promptly to fly to pieces, but not so with the diamond; the high heat conductivity of this remarkable substance permits it to submit to the sudden change of temperature without there resulting in it even the slightest flaw.

The dop is now fastened by means of its stem in a heavy iron arm called the tongs, in such a way as to bring the position of the facet to be cut exactly undermost when it is placed in contact with the polishing wheel or lap. The latter is made of soft iron and turns horizontally at the rate of about one thousand revolutions a minute. Diamond dust, mixed with olive oil, is fed to this wheel and the diamond is held in contact with it by weight of the tongs, aided by slabs of lead placed upon the latter. Several hours are required to cut one facet, then the stone is readjusted for another one, and so on until all of the fifty-eight little facets in which lies the secret of the brilliancy of the jewel are produced.

To appreciate the exquisite skill and infinite patience involved in this apparently simple process we have only to look at the gem on our finger, sending forth its magical fires, and to note the symmetry and regularity of shape of each of its tiny, glittering sides. And when we remember that to produce these rainbow-like rays each must have exactly the right tilt with respect to its neighbors, we realize that a cut diamond is not only a wonderful product of nature but a marvelous work of art.

Before the introduction of methods of diamond cutting in the fifteenth century, diamonds, when used in jewelry, were set with four of the eight sides of the octahedron or double pyramid projecting from the setting. This presented the aspect of a four-sided pyramid, and the exposed faces or facets were sometimes polished. The next step in the evolution of the modern form of diamond cutting was the production of a flat “table” on the exposed point by rubbing or “bruting” two crystals together. Thus we have the origin of the table facet as it is known today. In the early seventeenth century when the art of the diamond cutter had somewhat advanced, a more symmetrical outline for the stone was obtained by cutting away the four edges of the pyramid above the setting, which of course necessitated the equal cutting away of the four edges below.


The actual cutting of the facets on the diamond, known as “polishing,” calls for the highest expression of the diamond lapidary's art. The stems of the “dop,” which bear the diamonds, must be adjusted in the “tongs” with fine nicety. Here again the form of the tools has not changed in a century. The iron “tongs,” the wheel and its spindle (shown in the center of this picture), even the metal pegs against which the tongs are kept in place on the wheel, are the same as those used in Amsterdam and Antwerp in 1821.
This gave eight facets grouped about the table and eight below the "girdle," as the line encircling the stone at the point of the setting is called. At a previous stage in its development a small facet called the "culet," directly opposite the table, had been introduced, so that we have for this cutting, which has sometimes been called the single-cut brilliant, a total of eighteen facets. This gave eight facets grouped about the table and eight below the "girdle," as the line encircling the stone at the point of the setting is called. At a previous stage in its development a small facet called the "culet," directly opposite the table, had been introduced, so that we have for this cutting, which has sometimes been called the single-cut brilliant, a total of eighteen facets.

Up to this point in the development of diamond cutting, stones were cut for symmetry of outline alone and no attempt was made to utilize the remarkable optical properties of the diamond, which enable it, when properly proportioned in the cutting, to reflect back to the eye most of the light which falls upon it. Toward the close of the seventeenth century Vincenzio Peruzzi, a Venetian, began to cut diamonds on this principle. With this discovery, no longer the lapidary labored solely to produce a maximum weight and symmetry of outline, but he endeavored to combine with these the very essential factor of the brilliancy of the stone. And with increased skill in the art, more facets were added to beautify the form and enhance the radiance of the gem. Sixteen additional “corner facets” above and sixteen below the girdle rendered it rounder and more symmetrical, and subsequently eight extra facets grouped about the table completed the fifty-eight of the modern brilliant.

It is a singular and somewhat significant fact that the historical evolution of the modern brilliant as here traced is precisely its actual evolution under the hands of the diamond cutter. The facets are added to the stone in just the order in which they were developed through the centuries.

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