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Swiss lapis (occasionally called German lapis), is really stained jasper and is quite distinct from the mineral lapis lazuli. The jasper used is grayish-brown in color, often flecked with white, and different processes are used to change this uninteresting shade to a blue which approximates to some Chilean or Persian lapis lazuli. Whatever shade of blue is obtained, it always fades, whereas the natural lapis lazuli does not fade. It must be remembered, however, that poor quality lapis lazuli is also sometimes “helped” by soaking in a blue colored solution, and this also fades away to leave the blackish-blue or gray surface of the natural stone.
Incidentally, Swiss lapis never shows the inclusion of iron pyrites so often seen in lapis lazuli as gold colored specks, but apart from this, a dealer in semi-precious stones would never be misled by the color alone since it never corresponds to the lazuli blue. The Swiss lapis blue is obtained by various methods. One is the same that produces blue agate. A darker blue is made by adding a few drops of both concentrated sulphuric and nitric acids to the ferrous sulphate solution, or to the potassium ferro-cyanide.

Various chemical salts are used in staining chalcedony and agates. The green is produced by soaking either in a nickel salt solution or in a solution of chromic acid, and then heating. Or the stones may be immersed from a week to two months in a saturated solution of potassium dichromate, after which they are transferred to a closed container and exposed to the fumes of ammonium carbonate for two weeks. After drying, a gentle heat will produce the green color. For an apple green, a solution of nickel nitrate is used, and the ammonium carbonate treatment is omitted.

Lemon yellow colored stones are obtained by gently warming well dried specimens in hydrochloric acid for about ten to fourteen days in a regulated oven. The translucent, pale blue colored stones sold as “chalcedony” are stained with an ammonia compound, and its subsequent evaporation is the cause of the rapid fading. The dark blues, sold as blue agate, are obtained by soaking
first in a solution of ferric oxide and then in a solution of potassium ferrocyanide. A lukewarm solution is used, and one to two weeks are allowed for soaking. After washing, the agate is left for some days in a saturated solution of ferrous sulphate, re-washed, and then slowly dried.

The application of heat alone will accentuate the color of many agates and carnelians, but these are sometimes first impregnated with a solution of iron vitriol. The stones may be soaked in this liquid from two to four weeks, according to their thickness. If they are more than ten millimeters thick, success is doubtful. Drying and repetition is then resorted to, the drying being effected by gently heating from two to ten days in a closed receptacle. Both heating and cooling must be performed gradually, otherwise the stones fracture. Most carnelians and agates marketed have been so altered, including many Indian carnelians.

Rich brown tints, resembling some garnets, may be produced by soaking pale carnelians in brown sugar for some time and then carefully igniting. A necessary precaution at all times is first to remove all traces of oil and other matter. For this reason, the material about to be stained is generally bathed in caustic soda, dried, and then soaked in warm, dilute nitric acid for two or three days. The acid is gradually brought to boiling point, and continued repetition may be necessary to remove all iron and other stains.
The Chinese very rarely alter the stones which they work, and it can be taken as a general rule that Chinese jade and other stones which they work and carve are presented in their natural colors. Idar-Oberstein in Germany is the center of the staining and coloring of stones in Europe, and its products are to be found in every country.

Natural agate, which is a striped stone of a porous nature, takes a stain very easily. The white stripes are generally of a harder nature and not very porous, so after treatment the resulting stone may be one of a vivid blue, green, or red, with very marked white stripes which have not taken the stain. Agates are, of course, striped naturally, but the colors obtained are much deeper and more vivid than any that would be found in nature. The appearance of the stone is certainly made more attractive, and the dark blues, greens, and reds are almost permanent.

Onyx, a black and white striped type of quartz, is also treated to darken the black zones and so accentuate the differences in shades. The stone is first immersed in a solution of sugar or honey, which is kept at a constant temperature for several days, depending on the assumed porosity of the specimen. It is then taken out, washed, and soaked in warm sulphuric acid, the honey or sugar absorbed from the first soaking being converted into carbon. This gives the required black zones. It is fairly safe to assume that all agates and onyx showing marked differences of color within the one stone have been artificially treated; the natural stones are much less strongly colored.

The alteration by various artificial means of the natural color of stones is a recognized practice, but it is confined to a certain number of varieties, the chief of which is quartz. Colors are made more attractive, or a different color altogether may be introduced. In some instances, this alteration is permanent; in others, the color fades in course of time and with exposure to light. Blue is a particularly fugitive shade if artificially introduced.

In general, the addition of a color is only resorted to with stones of a porous nature. Some varieties are altered by heating alone, but the amount of heat necessary is a matter of experience and varies with individual stones. We have already noted the effect of heat on gem stones, and here we shall deal with improvement in color and quality from a commercial point of view by the use of this agent.
Such treatment of stones by a variety of processes is not a modern idea, for many writers, including Pliny, describe to us the different methods that were used many hundreds of years ago. Some of these methods still hold good; others have been improved, yet the majority of gem stones still come to us in their natural colors, just as they are found in the earth. One of the chief attractions of a gem stone, indeed, is the quality of its being perfectly natural, and there is a suspicion about anything of value that has been tampered with, or that has been altered in some way so that its commercial value has been increased. None of the precious stones, as far as is generally known, is subjected to alteration of color for commercial purposes, and the porous varieties of quartz, or chalcedony, constitute the main bulk of stones which have been improved or altered by artificial means. In general, these stones are among the least valuable of jewel stones (although by no means the least interesting), and poor material is often made more attractive by introducing a bright color or intensifying existing colors. Synthetic stones, of course, may be produced in any color, so the need for their alteration does not arise.

By reducing the depth of a stone, its color may be lightened, and a greater “spread” is often required to bring out the color in such varieties as dark sapphires and tourmalines. Again, absorption effects must be taken into consideration, particularly with tourmaline, which shows visible dichroism. A combination of the brilliant and step cut is known as the mixed cut. Here, the upper part is brilliant cut and the lower part is step cut.

The cabochon cuts, which involve curved and unfaceted surfaces, are rarely used with transparent stones, except the carbuncle garnet. The simple cabochon has a curved top and a flat base; the double cabochon has both a curved base and crown, and the hollowed cabochon (rarely seen except with carbuncle garnets) is curved above the girdle and hollowed out below. The hollowed cabochon is a favorite form with carbuncles since transparency is increased and color lightened by its use. With cabochons, the height of the crown varies; in moonstones, it is sometimes high to increase the milky sheen. Opals, star stones, cats’-eyes, and the opaque varieties of quartz are among the stones which are always cut en cabochon. There are no facets on the surface, as with other forms of cutting.

Double roses, both the crown and base being faceted, are now seldom seen. Rose cut stones are generally used to surrbund larger stones, and they are often found in moderately priced diamond set jewelry which contains a large number of stones, such as spray brooches. Besides being far less valuable than fully cut brilliants, they show comparatively little “fire,” especially if dirt or grease is allowed to accumulate on the base. Small cut stones varying in size are called “melee,” and they may range from eight to sixteen to the carat in weight. But small mel£e may be as minute as 400 stones to the carat.

The step, or trap, cut is commonly used with emeralds, sapphires, rubies, topaz, aquamarines, tourmalines, and other colored stones, particularly where the aim is to bring out the body color of the specimen and where the dispersion is not strong. Emeralds are very rarely cut in any other form, and this has given rise to the term “emerald cut.” The facets above and below the girdle are parallel and horizontal, the general shape of the stone being oblong, square, or octagonal.

Corresponding facets (pavilion facets) are now cut below the girdle; then eight star facets follow, these being triangular in sliape and pointed downwards from the octagonal sides of the table. Sixteen split facets are now made, these also being triangular in shape and their base being the girdle. There are now 33 facets —one table, eight bezel, eight star, and 16 split facets—which form the upper part of the full cut brilliant. As we have already noted, other names are sometimes applied to these facets.

The culet, collet, or culasse is the small facet made by the flattening of the sharp point on the bottom of the stone; this is now seldom seen in modern cut gems. Eight pavilions and quoins, and 16 split facets beneath the girdle are cut absolutely beneath, and corresponding to, those on the upper portion of the stone, although their length depends upon the individual specimen in hand. This completes the cutting, the finished stone now having 57 facets.

This brilliant cut brings out the “fire” in the stone, causes the light to be flashed back to the eye, and at the same time retains as much weight as possible. The stone is ready to be used in any form of jewelry, and its beauty will remain indefinitely. Repolishing of the facets may be advisable after much use, although with diamond this is very rarely necessary. It is of advantage, however, to keep the back of the stone quite clean in its setting and to remove any dirt or grease which inevitably collects in course of wear.

The rose cut is characteristic of very small, or poor quality, diamonds. It may be used on small fragments resulting from cleaving and sawing operations. Such small diamonds are often called “roses.” In this form, the base is flat, and this is often the cleavage plane; the top is curved, convex in shape, and this is covered with small facets up to 24 in number. There may be only five or seven facets in very small stones, while in others disproportionate faces may be seen. Badly cut roses of poor quality material are quite common, and they are often used in conjunction with brilliants in medium priced jewelry. The value of rose diamonds is, of course, far below that of the properly cut stone.

Generally, the colors of natural stones remain a permanent quality, but there are some which fade in time although they have not been artificially treated. Blue zircons, yellow and blue topaz, amethyst, and rose quartz are among those that will fade in strong sunlight or in course of ordinary wear. White zircons sometimes change to a dirty gray or brownish color, which was no doubt their original color before they were heated. Opals also should not be put in the strong sunlight, otherwise they might develop faults and lose some of their color, for this stone contains by nature an appreciable percentage of water.

The thickness of the crown should be one-third of the total thickness of the stone, and the table should be about four-ninths of the breadth of the stone. These proportions are based on the optical properties of the diamond, and it will be seen that a considerable amount of care and patience will be required to cut a given stone, which is generally quite small, to these specifications.

With other transparent stones, the facets are somewhat modified if cut in this form, and their number and inclination to each other will depend upon the individual optical properties of the specimen. Such stones as white zircon, white topaz, and white sapphire usually have fewer facets than the diamond. Sapphire and ruby are often brilliant cut, but usually without the full number of facets also. Emerald is seldom seen in brilliant form, since its color dispersion is low, and the trap cut brings out its color to better advantage.

We will now recapitulate the various facets of the brilliant form of cutting in the order of manufacture. First, a facet is cut which slopes from the table to the girdle. This is the bezel facet. Opposite this, another is cut, and a further two similar facets makes the table square in shape. Four more bezel facets follow, which makes the table octagonal.