History of use

How to distinguish real jet from a fake?

Bakelite is a phenolic resin formed at the initial stage of the synthesis of phenol-formaldehyde resin. It was the first true synthetic polymer. Its inventor, Leo Hendrik Baekeland, patented the formula in 1909. Bakelite was not immediately produced in sufficient quantities, so it was not used as widely as ebonite as a jet substitute. However, some amount of black bakelite was still used to make jewelry such as brooches, bracelets and beads. Bakelite beads had a round shape and were smooth – without cutting or carved patterns. Of all the decorations, they most misled specialists, making identification difficult. Bakelite weighs about the same as jet, has a deep black color, does not tarnish, and polishes well. When abraded, Bakelite turns into a black powder and leaves a black mark on the porcelain plate. Like other polymers, it can be molded by heating. If bakelite is set on fire or touched with a hot needle, the typical smell of phenol (carbolic acid) is felt. Bakelite is a dense material and does not break down as easily as jet. Therefore, a very perfect-looking piece of bakelite may arouse suspicion. Through the holes in jet beads, manifestations of conchoidal fracture are often visible. In plastic beads, the holes on the inside are perfectly round and smooth. Fortunately, most Bakelite jewelry (with the exception of beads) is stamped “Patent” on the back, eliminating the need to examine it.

The best samples of the mineral

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Jewelry stones and metals

Standard gemological tests are usually not applicable to the identification of jet. Optical studies do not play a big role due to its opacity. According to refractometry data, jet is characterized by a refractive index (R) of about 1,66. Its density fluctuates in the range of values ​​corresponding to many substances similar to jet.

Therefore, jet identification can only be done by process of exclusion. None of the existing methods allows one to accurately distinguish jet from all its natural and artificial imitations. Of course, this can be done using modern technological methods such as ultrasound, infrared spectroscopy and X-ray analysis, but these are intended for scientific research and are rarely available to the hobbyist or ordinary jeweler.

In the end, one has to resort to examining the jet or to very simple but destructive tests. These include scratching the surface with a steel needle, marking the color of a line on a matte porcelain plate, using a heated needle, or burning a small piece. All these methods are more or less destructive for jet and are unacceptable for samples that do not belong to the research analyst himself.

Thus, jet identification has to be done visually using a 10x magnifying glass. In the vast majority of cases, this is really all that the experienced collector needs.

1. Color. Although the color of jet is a very rough diagnostic sign, the phrase “jet black” has some meaning, since the color is indeed very deep and intense. No other coal-like substance is as black in color. In this regard, anthracite is perhaps closest to jet, but even in this case it does not have such a deep, velvety black color. Kennel coal has a silvery sheen. Kimmeridgian slate is usually brown or gray-black in color. Swamp oak and antler are more brown than black. Of the artificial imitations of jet, only bakelite comes close to it in color, and ebonite fades and becomes dull over time.

2. Thermal conductivity. Jet is characterized by low thermal conductivity, so touching it is always accompanied by a feeling of warmth. True, many substances that imitate it behave in a similar way. This feature, however, allows jet to be distinguished from the natural minerals onyx and chalcedony, which are cool to the touch because they are relatively good conductors of heat. Glass is cooler than jet, but inferior in this regard to natural minerals.

3. Electrical conductivity. In terms of its ability to become electrified by friction, jet differs from coal, Kennel coal and swamp oak. However, many plastics, especially bakelite, have a similar property.

4. Mass. Natural gemstones and glass are heavier than jet, and this can be easily determined by weighing. Most of the imitating materials differ little from it in weight. Density is not a diagnostic feature, since in terms of this property jet does not differ significantly from many of its “doubles”.

5. Kink. A slight conchoidal fracture is typical of jet. It appears on products over time. However, such a fracture is also typical for coal and glass. In addition, there are quite a few jet products with fractures or other types of cracks, and therefore this distinctive feature cannot be considered sufficiently reliable.

6. Design. Since plastic imitation jets are produced by molding, it is possible to produce many copies. This is especially true of ebonite, products from which were apparently produced in large quantities in the 7th century. For this reason, the same design (sketch of a product) can be reproduced many times, and it is not difficult to discover that the product is made of ebonite. An example of this are earrings in the form of pendants with a bead at the end. Sometimes such earrings were made in the form of a cameo depicting a human head, or a vine. Such sketches were so common that they were easily recognized in photographs without resorting to the original. Thus, in one of the books devoted to Victorian jewelry, there are XNUMX illustrations of products passed off as jet, which are actually made of ebonite.

7. Production method. All genuine jet products are handmade, while the imitation ones are molded. This is undoubtedly one of the most important distinguishing features. Craftsmen hand-carved inscriptions along the edges of their high-relief products. Molded products, on the other hand, do not have any traces of carving. They have smoothed edges and low relief. However, some plastic products are distinguished by excellent artistic performance. For example, an ebony medallion inside under glass was always skillfully decorated, while a similar jet medallion was, as a rule, more austere and not polished.

1. Powder color and features on matte porcelain plate. These tests can be carried out simultaneously, since in both cases the assessment is given by color. Lightly scratching a product with a steel needle leads to a double effect. Firstly, the material reacts to this action in a certain way: the needle slides smoothly over the surface of plastic products and experiences obvious inhibition when scratching a jet product. In the latter case, you have to increase the pressure. Secondly, the color of the resulting powder is characteristic. For jet it is always brown, never black. However, a brown powder is also obtained by abrading lignite (of no value to a jeweler), bog oak (which is determined by other methods) or ebonite.

Similar colors leave products on a matte porcelain plate. This type of testing is the least destructive for products.

2. Cauterization of products. With a sharp knife you can pick out a small piece and set it on fire. Since this procedure causes damage to the product, it is preferable to use a hot metal needle. This method is the most reliable of all types of tests, but, unfortunately, is only applicable to the purchased product. Antiques dealers half-heartedly welcome buyers who want to test the items they sell with a hot needle. However, some of them still express a desire to check the quality at least on a porcelain plate.

In most cases, a cursory examination of the products is sufficient for identification, since, in essence, only a very small number of them raise doubts and require careful examination.

Generally speaking, only archaeologists deal with products made from lignite, Kimmeridgian slate and Kennel coal. Mostly plastic products pass through the hands of jewelers and collectors, among which the biggest problem is ebonite. Since both jet and ebonite produce a brown powder when abraded, the only way to distinguish them from each other is by testing with a hot needle. In the first case, the smell of burning coal is clearly felt, while in the second there is a distinct smell of burnt rubber.

If, for example, you happen to have a set of black beads, then by ordinary weighing you can immediately distinguish among them products made from natural black minerals – onyx, chalcedony, black tourmaline and garnet. In typical Irish decoration, which successfully combines brown and unpolished fragments, it is easy to recognize swamp oak. But glass (“French jet”) and enamel cannot be scratched with a metal needle. In this case, the horn produces a gray powder.

By scratching with a needle, it is not difficult to determine the wood base of materials such as bois durci and painted wood. Bakelite, all varieties of slates and coals produce a black powder and leave a black line on the matte porcelain plate. Lignite has a woody structure and is characterized by a brown color. Jet and ebonite leave the same color line. These materials can be identified in products if they are hand-cut or molded, but if these products have been damaged, the most reliable way to determine their authenticity is with a hot needle.

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