What chemicals are used in jewelry

Gemstone

This article explains jewelry or precious stones; For further meanings of the word "gemstone", see the definition of terms under "gemstone".

Gemstones, partly also as Gemstones are minerals, rocks or glass melts that are generally perceived as beautiful and are used as jewelry, but also substances of organic origin, such as amber, pitch coal or relatively small and elegant fossils. According to the definition of the international trade organization CIBJO, pearls, mother-of-pearl and corals also count among the gemstones.

The study of precious stones and gemstones is called gemology.

Selection of different gemstones. The largest specimen measures around 40 mm

General story

Stones have also been used as jewelry since the Paleolithic Age. In ancient times, precious stones were processed into jewelry in addition to gold, silver and other materials.

Gemstones were ruby, emerald, sapphire and beryl. Amber was also used as a gemstone. Since gemstones were usually of considerable value, they were not infrequently forged. The color of some minerals, such as agate, has been changed by burning or coloring. These and some other traditional improvements do not have to be declared, whereas changes in color due to exposure to electromagnetic waves always have to be declared.

In ancient times and the Middle Ages, jewels were only cut more or less round, the facet cut did not appear until the early modern era. The diamond also only became a gemstone in modern times, while in antiquity it was used by craftsmen because of its hardness, for example for carving gems.[1]

Minerals

Minerals of the appropriate quality are often used as precious stones or gemstones. Depending on the type of mineral (e.g. diamond, corundum, malachite), different criteria are used to determine the quality. Often the transparency, purity, rarity and color determine the use and the value. One of the most valuable gemstones, the diamond, has four properties (4 C), the cut, the weight in carat, the color and the clarity, of which only the first can be directly influenced by humans. Changes in color must be declared. Some minerals have inclusions that reduce the value of the stone, but can also increase it. The location can also make a difference in fine details of the individual characteristics, which in turn reveal the origin of the stone to a specialist.

Gemstones are partially treated with heat or radioactivity in order to improve or change their optical properties. For example, the color of some amethysts changes from purple to yellow after heat treatment. The treated mineral is then marketed as "citrine". In Germany, these artificially treated minerals must be labeled accordingly.

Jewelery-quality minerals are also produced synthetically, for example quartz with its amethyst or corundum variety. The quality of synthetic diamonds has been greatly improved in recent years, so that some of them are now also used as synthetic gemstones.

Gemstones

Selection of faceted cuts

Gemstones are gemstones that meet the following three criteria:

  • rarity
  • Hardness> 7 according to Mohs
  • transparency

Well-known types of gemstones are, for example, ruby, sapphire, emerald and topaz. A diamond is a special crystalline form of elemental carbon. According to the above definition, it also belongs to the gemstones today, while it had no special value as a gemstone in the Middle Ages[2] and mostly only the colored stones were referred to as gemstones.[3]

Today, precious stones are usually cut into shapes that increase light reflection and enhance the shine through the quality of the polish, but also to give the mineral a shape suitable for further processing in jewelry. Only brilliant-cut diamonds are referred to as brilliant-cut diamonds, other brilliant-cut types of gemstone must be supplemented with the gemstone name.

classification

Collection of precious stones

In addition to the classification features already mentioned above, such as light permeability, purity and color, there are also the following criteria, which are based on the criteria of mineral determination:

The criteria used include the chemical composition, diamonds, for example, consist of carbon, rubies of chrome-colored aluminum oxide (Al2O3). Furthermore, gemstones are also differentiated according to their crystal system, the type of crystal lattice, which can be cubic, trigonal or monoclinic, for example. The so-called habitus, the form in which the gemstone can be found in nature, is another classification criterion.

Gemstone types are often further subdivided into different varieties, which mainly depend on the color. For example, red corundum is traded as ruby, a special red-orange as padparadscha. The remaining colors are called sapphire, the blue sapphire being the most valuable. Diamonds can also come in different shades, which are then known as "fancy diamond". The varieties of beryl can be found as emerald (green), aquamarine (blue), red beryl (also obsolete Bixbit, red), goshenite (colorless), golden beryl (lemon yellow to golden yellow) or Heliodor (light yellow green) or morganite (also Rosaberyl). Heliodor However, it is sometimes rejected as an independent beryl variety and counted among the gold beryls.[4]

Physical differences manifest themselves in the refractive index, the dispersion, the specific density, the hardness, cleavage, brittleness and the gloss. Gemstones like tourmalines can show different colors or be birefringent due to pleochroism in different directions. Their absorption spectrum is also characteristic.

After all, its size also plays an important role in determining the value of a gemstone.

Treble clef made from gem stones

"Semi-precious stones"

Semi-precious stones used to be called minerals, which are characterized by their beauty, but in contrast to precious stones occur much more frequently in nature. They are usually not as hard and less valuable than gemstones. Today we speak exclusively of gemstones or gemstones. The term semi-precious stones is out of date and should no longer be used in mineralogy and gemology. It indicates a certain inferiority, which is actually not there.

classification

The usability and the value of a gemstone / gemstone are based on criteria that are very dependent on the type of mineral. For ores such as hematite and pyrite there are no other criteria than gloss and, under certain circumstances, shape. In the case of garnets, quartz and other minerals, as with gemstones, transparency, purity and color play a role

Manipulations and imitations

Many minerals or rocks that are used as gemstones are manipulated in various ways in order to improve their properties (color, shine, durability) and thus make them more desirable or to imitate other rare and valuable gemstones.

Oils / fats

One of the oldest methods of repairing stones is to oil them to cover up cracks. The stone appears more transparent and the colors brighter and more intense (compare between wet and dry river pebbles). The oils used range from animal oils (whale rat, tallow) to vegetable fats (vegetable oil, olive or sunflower oil) to synthetic oils and even baby oil (Vaseline).

Oiled stones "sweat" the oil easily when heated, and it dries up over time. Both lead to staining and loss of gloss. Oiled rough stones and minerals can possibly become completely unusable due to the formation of an ugly, non-washable coating. The additive is only valid when using colored oils colored Mandatory. However, among collectors it is not considered correct to offer such pieces without labeling, as the optical impression of the pieces (which determines their value!) Is significantly changed.

Waxing / paraffining

Instead of using oil, you can also use wax or paraffin to cover cracks and increase shine and color. Paraffinization is a little more durable and is mainly used for opaque gemstones and tumbled stones. However, the wax will also wear away over time through use or strong heat radiation. The waxing, if it is colorless, does not have to be specified in the trade. This method is also not considered by collectors.

Stabilize

Soft, porous or coarse-grained gemstones are treated with a coating of resin or synthetic resin to protect them from damage from scratches and chemicals (sweat, soap). However, the color can also be changed here by using colored resins. Stabilized gemstones must have the addition treated wear.

Reconstructions

Reconstructions are particularly common with opaque stones, but this method is also popular with amber. Here pulverized material or small fragments are either fused together (amber), sintered (hematite) or glued with a suitable binding agent (malachite, turquoise). Reconstructions of amber can be called "real amber", whereas hematite is renamed hematin. All other gemstones that do not have a separate trade name must be described as "reconstructed".

To dye

Gemstones with an undesirable or too pale color are recolored using various, mostly superficial, methods in order to enhance them. All colored gemstones must also be designated as such.

Colored oils, waxes or plastics
are common means of recoloring gemstones. However, only porous stones can be colored through or at least deeply colored. With all others, the colorant is on the surface or, in the case of cracked stones, no more than a few millimeters deep. For example, agates are heated in a color solution for a long time, and carnelian is then burned in order to achieve the final color nuance and to fix the colorant. Superficially colored stones rub off over time, especially with frequent body contact.
Steaming
is a very durable and difficult to recognize way of dyeing, which also creates an iridescent effect. The treated mineral (rock crystal, topaz) is vaporized with metal, mostly gold.
Soaking in sugar solution
and subsequent dehydration (dehydration) is mainly used for agate and black opal in order to imitate the rare onyx. However, the black color of black opal is naturally only a few millimeters thick in order not to destroy the water-containing mineral during dehydration.

Burn

Firing means that the raw gemstones are heated up to several hundred degrees Celsius in order to change their color and transparency. Coloring, metallic inclusions are oxidized, crystallization errors and thus cloudiness are dissolved. Depending on the temperature and burning time, different gemstones can be given different shades of color. When amethyst is converted into citrine, for example, it takes on a light yellow color at a temperature of around 470 ° C, but a dark yellow to red-brown color between 550 ° C and 560 ° C. Smoky quartz can sometimes be converted at 300 to 400 ° C. Firing changes the stones permanently, but is difficult to detect and does not have to be specified.

Particularly lucrative is the burning of certain inexpensive, milk-white sapphires, so-called geuda, to a cornflower blue color. An increase in value of 10 to 100 times is possible. Even stones that have already been faceted can be fired in this way if they have few inclusions.

Irradiate

Irradiation with X-rays or radioactive rays (gamma, neutron or, more rarely, alpha rays) also serves to change the color, which can be very strong but, unlike burning, is not always permanent. In addition, radionuclides are formed in the stone when irradiated with neutrons, which can make the gemstone radioactive under certain circumstances. You must therefore be in quarantine until the radiation subsides, which can sometimes take a few years. All gemstones modified in this way must have the addition treated or irradiated wear.

synthesis

Some minerals can be produced artificially (synthetically) from the corresponding basic elements, for example using the Verneuil process. To produce certain minerals, however, additional heat and pressure are required. The diamond is the best example of this, but many other minerals are now also being synthesized in very good quality and show only minor differences from their natural models. In addition to diamonds, syntheses of rubies and sapphires, emeralds, various quartz and opals are particularly widespread. All syntheses must be marked as such.

Nowadays, toy stores offer special chemical kits which, however, only produce crystals with a gem-like appearance (mostly through recrystallization of potassium alum or similar, harmless salts and any color additives from saturated aqueous solution).

Syntheses are often used for costume jewelry because, in contrast to their naturally created models, they are usually cheaper to manufacture. In this way, inexpensive pieces of jewelery can be produced whose artificially produced syntheses can hardly be distinguished from real gemstones.[5]

Imitations

Since many minerals look very similar, especially in color, rare and therefore expensive minerals are often imitated by more frequent and therefore cheaper minerals. A common imitation is synthetic spinel, which can be made in many colors. It is even easier to create imitations using glass or ceramics. In order to be able to distinguish real gemstones from forgeries, their physical properties have to be analyzed.

Doublet / triplet

Structure of a doublet / triplet
1. Gemstone
2. Document
3. Edition

A special case of imitation is the doublet or triplet, which consists of composite layers of real gemstone and glass, syntheses, quartz or other solids. With this method, you can make many stones from a small amount of basic material. Although it is z. B. Used real opal, but it is a massive manipulation of the stone. Triplets and doubles must be declared.

Duplicates are a thin layer of the real gemstone that is glued to a base made of obsidian, various iron stones, potch (opaque opal without play of colors) or plastic. This protects the sensitive stones from body and sweat contact, among other things. With triplets there are two covering layers, the base protects against body contact, the top layer against scratches and drying out and is therefore particularly often used for opals. In order to be able to recognize doublets or triplets, the stone usually has to be removed from the setting.

ID

In order to find out forgeries, manipulations or imitations, the density or, in the case of translucent minerals, the refractive index of the gemstones to be examined can be used. A refractometer is used to determine the refractive index. Another method are spectroscopic examinations with which the spectral distribution of the characteristic absorption lines in the absorption spectrum can be analyzed.

A simple method for roughly determining the refractive index is also the so-called immersion method, in which the gemstones to be tested are immersed in liquids with a known refractive index. These make the contours of the immersed object disappear if the refractive index matches.

Certain gemstones can also be identified with the help of fluorescence. The two ultraviolet wavelength ranges between 200 and 280 nanometers and 315 and 400 nanometers are mainly used for light excitation. The stones then shine in characteristic colors in visible light.

Esotericism

Many gemstones are used as healing stones in esotericism or are intended to protect against bad influences in amulets.

See also

  • List of mineral jewelry and precious stones
  • Cabochon
  • strass

literature

  • Bernhard brother: Finished stones. Neue Erde Verlag, 1998, ISBN 3-89060-025-5.
  • Florian Neukirchen: Gemstones: Brilliant witnesses to the exploration of the earth. Springer Spectrum, Heidelberg 2012. ISBN 978-3-8274-2921-6.
  • Walter Schumann: Precious and semi-precious stones. 6th edition, BLV Verlags GmbH, Munich 1976/1989, ISBN 3-405-12488-3.

Web links

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Individual evidence

  1. ↑ Ruhr-Uni-Bochum, project Diamond: the magic and story of a gift from nature, Brochure Rubin 1/03.
  2. ↑ cf. Jan Hirschbiegel: Étrennes, P. 154, footnote.
  3. ↑ cf. Alois Haas, Ludwig Hödl, Horst Schneider: Diamond: the magic and story of a natural wonder, P. 78.
  4. ↑ Walter Schumann: Precious and semi-precious stones. All species and varieties in the world. 1600 unique pieces. 13th revised and expanded edition. BLV Verlags-GmbH., Munich and others 2002, ISBN 3-405-16332-3, p. 112.
  5. ↑ J. Liebertz: Synthetic gemstones . Springer Berlin / Heidelberg, 2004, ISSN 0028-1042