How does a diamond decrease in value
What does dispersion mean in the case of diamonds and other precious stones?
The term dispersion comes from the field of physics and indicates how incident light can be converted into a color spectrum through refraction in different materials. The resulting colors depend, among other things, on the structure of the surfaces of precious stones such as diamonds. The frequency of the incident light also plays an important role. The third influencing factor is the speed with which light can propagate in different materials. A distinction is made between normal and abnormal dispersion. A normal dispersion has glass, for example, where blue light is refracted much more intensely than red light. If the refraction intensity decreases as the frequency of the light waves increases, the person skilled in the art speaks of anomalous dispersion. This phenomenon was discovered in 1870 by a Danish physicist named Christian Christiansen.
Why diamonds have the most interesting form of dispersion
The diamonds have an almost ideal refraction of the inherently colorless light when they are colorless themselves. In the case of gemstones with an intrinsic color, the colors of the rainbow normally generated by ideal refraction are falsified by their intrinsic color. The light hitting a diamond has different wavelengths. Each wavelength range is transformed into a physically predetermined color by a diamond. The grinder has an enormous influence on the colors in which a diamond can sparkle. In the technical language of diamond cutters and diamond dealers, this play of colors is also called "fire". The best possible fire can be created with a diamond with a multi-faceted cut. However, this requires the utmost precision.
The dispersion as the basis for determining the gemstones
The dispersion, also known as the refractive index, has been used for some time to determine the individual types of gemstones. The basis for this are the values of the BG dispersion, which compares the refraction of long-wave red light on the one hand and the refraction of short-wave ultraviolet light on the other. In addition, the ratio of the orange hues and the blue-green hues is used as the so-called CF value to determine the gemstones. Real diamonds have a CF value of 0.025. The BG value given for diamonds is 0.044. The code number of the BG dispersion is 0.039 for zirconium and 0.051 for titanite. A dermantoid can be recognized by the value of 0.057 in the BG dispersion.
What are inclusions in diamonds and other gemstones?
In the science of mineralogy, inclusions are also called inclusions. Inclusions can arise in two different ways, which those skilled in the art refer to as primary inclusion and secondary inclusion. With primary inclusion, foreign bodies are stored while the diamonds and gemstones are still being formed. Secondary inclusions occur when foreign substances accumulate in existing spaces after the crystal formation is complete. In primary inclusion, the crystals of the gemstones grow around crystals made from other materials. One of the best-known representatives of this type of inclusion is the rutile needle.
Which inclusions are common in gemstones?
Different types of inclusions are found in gemstones from rubies to amber to diamonds. The inclusions can just as easily be the crystals of other gemstones as liquids or gases. Gaseous and liquid inclusions are called fluid inclusions. They occur in both primary and secondary inclusion. The inclusions give clues to the origin of the diamonds and other precious stones. In addition, they have a considerable influence on the appearance and especially on the type of dispersion of the gemstones that can be found.
How do inclusions affect the quality and value of the gemstones?
The specimen that does not show any inclusions counts as a particularly high-quality diamond. These pieces are called flawless diamonds, or IF diamonds for short. Of course, they must not have any cracks or other impairments of quality. The degree of purity of diamonds and other precious stones is assessed with a tenfold magnification under the microscope.
According to the number and size of the inclusions, gemstones are assigned to three different categories. The flawless diamond or another gemstone belongs to type I according to this quality classification. There are also many aquamarines and blue topaz, for example. Type II already shows a considerable number of inclusions. Typical representatives of this group are the amethyst and the ruby. Emeralds belong to type III due to their consistently occurring inclusions.
It is not possible to draw conclusions about the expected price for every type of gemstone by assigning it to the types of inclusion. In the case of some gemstones, the inclusions make the special visual appeal. Here, specimens with interesting inclusions can certainly have a higher sales value than flawless specimens. Precious stones are particularly popular, which with their existing inclusions cause the so-called asterisk effect when the light is refracted. It is exactly the opposite with diamonds: the better their degree of purity, the higher the prices that can be achieved for the diamonds.
What is fluorescence in gemstones?
Some materials are able to spontaneously emit light themselves shortly after being irradiated with light. However, less light energy is emitted than was previously absorbed. Since this phenomenon was first discovered in fluorspar, also known as fluorot, it was given the scientific name fluorescence. The Irish physicist and mathematician George Gabriel Stokes is considered the discoverer of spontaneous light emission. The scientist, born in Skreen in 1819, first described the physical phenomenon that occurs in various gemstones in 1852.
How does the fluorescence of gemstones and diamonds come about?
So far, a total of around 200 different minerals are known where fluorescence can occur. The intensity and duration of the fluorescence in diamonds and other precious stones always depends on the individual type of inclusions. Materials in which fluorescence occurs are called fluorophores by scientists. The period of "afterglow" is called fluorescence lifetime in technical terms. It is usually only a few nanoseconds. The physical basis of fluorescence is that a fluorophore absorbs photons from the incident light. This stimulates these substances. In order to be able to return to the initial state, the amount of energy absorbed must be released again. This takes place either via fluorescence in the form of light or via vibration relaxation. With some materials a combined emission of the electromagnetic radiation obtained before can be observed. The specialist calls the pure relaxation of gemstones and diamonds via the emission of light photoluminescence.
The fluorescence in the determination of gemstones and inclusions
The material of the gemstones and the inclusions they contain determine how long the fluorescence effect lasts and in which colors it appears. Blue, yellow, green, orange, red and white are possible here. This is the main reason why measurement and evaluation of fluorescence is used to determine the type of gemstones and the inclusions they contain. If diamonds come into the area of influence of the UV radiation contained in daylight, they usually have a fluorescence in shades of blue. With diamonds, fluorescence effects usually lead to a decrease in value, as this impairs the optimal play of colors, also known as fire, that can be achieved through the cut.
When are diamonds and gemstones flawless?
Diamonds and gemstones are called flawless if, when magnified ten times in a dark field, no impairment of the ideal crystal structure can be seen. A diamond may only be declared flawless if there are no inclusions in it and no cracks can be seen. A standard was developed in 1952 to classify the quality of gemstones and especially diamonds. It comes from the Gemological Institute of America, or GIA for short, and is now used around the world to evaluate diamonds.
What quality grades are there for diamonds other than flawless?
A total of eleven different quality levels for diamonds have now been established in practice. Here is a quick overview:
The identification FL is only allowed to be given to diamonds which, when magnified ten times, show neither inclusions nor external impairments. In the IF group, tiny surface traces resulting from processing are allowed. The identifiers of the groups WS1, WSI and WS2 allow inclusions that are very difficult to see when magnified ten times. The addition “very” is omitted for groups VS1 and VSI. Inclusions and impairments that can be seen under the microscope may contain diamonds of quality groups VS2, SI1 and SI2. Anyone who buys diamonds of the quality grades PI1, PI2, and PI3 must expect inclusions and defects that are also visible to the naked eye. The following applies: The higher the number after the abbreviation PI, the more clearly the crystal defects and inclusions are recognizable.
When is a diamond no longer considered flawless?
A diamond is no longer classified as flawless if its appearance is only minimally impaired. Even the tiniest flaws below the table prevent a diamond from being classified as flawless. The reason is that mistakes at this point affect the fire of the diamonds particularly badly. In the case of inclusions and defects in the crystal structure of the diamonds at this point, unwanted light reflections often occur due to the side-cut facets.
What role does Mohs hardness play in gemstones?
The information on the Mohs hardness for gemstones and diamonds provides information about which material another material can be processed with. The classification developed by a mineralogist who was born in Germany and later worked in Austria and Italy does without any unit. Friedrich Mohs created ten different degrees of hardness, in which the following applies: For any material with a higher Mohs hardness, the surfaces of all materials with a lower Mohs hardness can be changed mechanically without further aids. The mineralogist classified the Mohs hardness after him exclusively through practical tests. His findings were later substantiated by the determination of the grinding hardness by the Austrian geologist August Rosival and the so-called Vickers method for hardness determination.
What is the structure of the Mohs hardness?
The lowest level of Mohs hardness is found in all materials whose surfaces can be scraped off with bare fingernails. For materials with a Mohs hardness of 2, grooves can be scratched into the surface with a fingernail. The group of substances with a Mohs hardness of 3 can withstand fingernails, but no longer withstand a copper coin. The fabrics with a Mohs hardness of 4 and 5 can be scratched with a pocket knife with varying degrees of effort. From a Mohs hardness of 5, a steel file is required for processing. From group 7, materials are classified that can be used to scratch commercial window glass. Gemstones such as topaz have a Mohs hardness of 8. Rubies and sapphires have a Mohs hardness of 9.
Why does diamond have a Mohs hardness of 10?
The diamond has a Mohs hardness of 10 because it can process all other materials. The only exception for minerals of natural origin is silicon carbide. In addition, diamonds can be worked with boron nitride, which occurs naturally in three different crystal structures and has the same Mohs hardness as diamond. The man-made aggregated diamond nanorods, also known as ADNR for short, have an even greater Mohs hardness than natural diamonds. They have a particularly small distance between the bonding of the carbon atoms and therefore a density that is eleven percent higher than that of naturally occurring diamonds. ADNR is made in industry from carbon atoms with extremely high symmetry called C60 fulleromes.
The phosphorescence ensures an afterglow of the gemstones
In physics, phosphorescence is classified as a special type of luminescence. The physicist describes luminescence as the relaxation of a substance charged with energy through the emission of light. This also includes fluorescence, which differs from phosphorescence in the length of time it lights up. With fluorescence, the emission of light only lasts for a very short time and the glow usually goes out after a few milliseconds. The afterglow in phosphorescence can last for several hours. This physical phenomenon is used, for example, when signposting escape routes. In the range of gemstones, it is valued as a particularly desirable extra.
How do the luminophores get into gemstones and diamonds?
The basic materials of diamonds and other types of gemstones cannot shine by themselves. The inclusions of foreign substances, which are also called inclusions in technical terms, are responsible for this effect. In order to achieve afterglow, the inclusions must be materials that contain phosphorus. This chemical element is the namesake for the afterglow, which was first described in 1602 by the Italian alchemist Vincentio Casciolo for barium sulfide. Hennig Brand was able to prove that phosphorus is responsible for this in 1669. A whole range of such luminescent pigments have now been discovered. Most of these luminescent pigments belong to the groups of calcium sulphides and zinc sulphides, which are involved as inclusions in the formation of gemstones and diamonds or can accumulate in cracks and cavities after the crystal formation is complete.
What depends on the colors in which gemstones and diamonds glow?
Which colors the luminescent pigments bring out depends on the type of substances contained in the inclusions of the diamonds and precious stones. ZnS pigments containing copper, for example, cause a greenish shimmering afterglow. Alkaline earth aluminates and alkaline earth silicates, which are included in diamonds and gemstones, cause a beige afterglow, while calcium sulfide ensures that the gemstones have a delicate reddish afterglow. One of the best-known representatives of gemstones with a strong red afterglow is the Hope Diamond, which is blue in daylight. The evaluation of the phosphorescence is not suitable for determining the types of gemstones, since the foreign substances can be stored in all gemstones in the same way.You are here:
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