Diamond cutting is the practice of changing a diamond from a rough stone into a faceted gem. Cutting diamond requires specialized knowledge, tools and techniques because of its extreme difficulty; the first guild of diamond cutters and polishers was formed in 1375 in Nuremberg and led to the development of various types of "cut". This has two meanings in relation to diamonds; the first is the shape: square, so on. The second relates to the specific quality of cut within the shape, the quality and price will vary based on the cut quality. Since diamonds are one of the hardest materials, special diamond-coated surfaces are used to grind the diamond down; the first major development in diamond cutting came with the "Point Cut" during the half of the 14th century: the Point Cut follows the natural shape of an octahedral rough diamond crystal, eliminating some waste in the cutting process. Diamond cutting, as well as overall processing, is concentrated in a few cities around the world; the main diamond trading centers are Antwerp, Tel Aviv, Dubai from where roughs are sent to the main processing centers of India and China.
Diamonds are cut and polished in Surat and the Chinese cities of Guangzhou and Shenzhen. India in recent years has held between 19–31% of the world market in polished diamonds and China has held 17% of the world market share in a recent year. Another important diamond center is New York City; the diamond cutting process includes these steps. Diamond manufacturers analyze diamond rough from an economic perspective, with two objectives steering decisions made about how a faceted diamond will be cut; the first objective is that of maximum return on investment for the piece of diamond rough. The second is how the finished diamond can be sold. Scanning devices are used to get a 3-dimensional computer model of the rough stone. Inclusions are photographed and placed on the 3D model, used to find an optimal way to cut the stone; the process of maximizing the value of finished diamonds, from a rough diamond into a polished gemstone, is both an art and a science. The choice of cut is influenced by many factors.
Market factors include the exponential increase in value of diamonds as weight increases, referred to as weight retention, the popularity of certain shapes amongst consumers. Physical factors include the original shape of the rough stone, location of the inclusions and flaws to be eliminated; the weight retention analysis studies the diamond rough to find the best combination of finished stones as it relates to per carat value. For instance, a 2.20 carat octahedron may produce either two half carat diamonds whose combined value may be higher than that of a 0.80 carat diamond + 0.30 carat diamond that could be cut from the same rough diamond. The round brilliant cut and square brilliant cuts are preferred when the crystal is an octahedron, as two stones may be cut from one such crystal. Oddly shaped crystals, such as macles are more to be cut in a fancy cut—that is, a cut other than the round brilliant—which the particular crystal shape lends itself to. With modern techniques, the cutting and polishing of a diamond crystal always results in a dramatic loss of weight, about 50%.
Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the weight. Since the per-carat price of a diamond shifts around key milestones, many one-carat diamonds are the result of compromising Cut quality for Carat weight. In colored diamonds, cutting can influence the color grade of the diamond, thereby raising its value. Certain cut shapes are used to intensify the color of the diamond; the radiant cut is an example of this type of cut. Natural green color diamonds most have a surface coloration caused by natural irradiation, which does not extend through the stone. For this reason green diamonds are cut with significant portions of the original rough diamond's surface left on the finished gem, it is these naturals. The other consideration of diamond planning is how a diamond will sell; this consideration is unique to the type of manufacturer. While a certain cutting plan may yield a better value, a different plan may yield diamonds that will sell sooner, providing an earlier return on the investment.
Cleaving is the separation of a piece of diamond rough into separate pieces, to be finished as separate gems. Sawing is the use of a diamond laser to cut the diamond rough into separate pieces. Bruting is the art of cutting a diamond round. In the modern era diamonds are rounded using either a laser. Industrial diamonds can be used for bruting a diamond round. Modern computer software measures the roundness of each diamond and "Ideal Cut" diamonds have to round within a 10th of a millimeter to qualify as an excellent cut diamond. Diamond polishing is the final polishing of the diamond. In a diamond factory one would find a diamond "Crossworker" who first places the main facets on a diamond; this is done to ensure maximum weight and best angles for the specific shape of diamond. After initial crossworking is complete, the diamond is finalized by smoothing the main facets by the crossworker, known as polishing the diamond. After the main facets have been polished by the crossworker, the final facets are polished onto the diamond by a "Brillianteer."
The facets added are the stars and bottom halves known as upper and lower girdle facets. The final stage
A chemically pure and structurally perfect diamond is transparent with no hue, or color. However, in reality no gem-sized natural diamonds are perfect; the color of a diamond may be affected by chemical impurities and/or structural defects in the crystal lattice. Depending on the hue and intensity of a diamond's coloration, a diamond's color can either detract from or enhance its value. For example, most white diamonds are discounted in price when more yellow hue is detectable, while intense pink diamonds or blue diamonds can be more valuable. Of all colored diamonds, red diamonds are the rarest; the Aurora Pyramid of Hope displays a spectacular array of colored diamonds, including red diamonds. Diamonds occur in a variety of colors—steel gray, blue, orange, green, pink to purple and black. Colored diamonds contain interstitial impurities or structural defects that cause the coloration, pure diamonds are transparent and colorless. Diamonds are scientifically classed into two main types and several subtypes, according to the nature of impurities present and how these impurities affect light absorption: Type I diamonds have nitrogen atoms as the main impurity at a concentration of 0.1%.
If the nitrogen atoms are in pairs they do not affect the diamond's color. If the nitrogen atoms are in large even-numbered aggregates they impart a yellow to brown tint. About 98% of gem diamonds are type Ia, most of these are a mixture of IaA and IaB material: these diamonds belong to the Cape series, named after the diamond-rich region known as Cape Province in North Africa, whose deposits are Type Ia. If the nitrogen atoms are dispersed throughout the crystal in isolated sites, they give the stone an intense yellow or brown tint. Synthetic diamond containing nitrogen is Type Ib. Type I diamonds absorb from 320 nm, they have a characteristic fluorescence and visible absorption spectrum. Type II diamonds have no measurable nitrogen impurities. Type II diamonds absorb in a different region of the infrared, transmit in the ultraviolet below 225 nm, unlike Type I diamonds, they have differing fluorescence characteristics, but no discernible visible absorption spectrum. Type IIa diamond can be colored pink, red, or brown due to structural anomalies arising through plastic deformation during crystal growth—these diamonds are rare, but constitute a large percentage of Australian production.
Type IIb diamonds, which account for 0.1% of gem diamonds, are light blue due to scattered boron within the crystal matrix. However, a blue-grey color may occur in Type Ia diamonds and be unrelated to boron. Not restricted to type are green diamonds, whose color is caused by GR1 color centers in the crystal lattice produced by exposure to varying quantities of radiation. Pink and red are caused by plastic deformation of the crystal lattice from pressure. Black diamonds are caused by microscopic black or gray inclusions of other materials such as graphite or sulfides and/or microscopic fractures. Opaque or opalescent white diamonds are caused by microscopic inclusions. Purple diamonds are caused by a combination of high hydrogen content; the majority of diamonds that are mined are in a range of pale yellow or brown color, termed the normal color range. Diamonds that are of intense yellow or brown, or any other color are called fancy color diamonds. Diamonds that are of the highest purity are colorless, appear a bright white.
The degree to which diamonds exhibit body color is one of the four value factors by which diamonds are assessed. Diamonds have a color grading system; this system goes from D to Z. The more colorless a diamond is, the rarer and more valuable it is because it appears white and brighter to the eye. Color grading of diamonds was performed as a step of sorting rough diamonds for sale by the London Diamond Syndicate; as the diamond trade developed, early diamond grades were introduced by various parties in the diamond trade. Without any co-operative development these early grading systems lacked standard nomenclature, consistency; some early grading scales were. Numerous terms developed to describe diamonds of particular colors: golconda, jagers, blue white, fine white, gem blue, etc. Refers to a grading scale for diamonds in the normal color range used by internationally recognized laboratories; the scale ranges from D, colorless to Z, a pale yellow or brown color. Brown diamonds darker than K color are described using their letter grade, a descriptive phrase, for example M Faint Brown.
Diamonds with more depth of color than Z color fall into the fancy color diamond range. Diamond color is graded by comparing a sample stone to a master stone set of diamonds; each master stone is known to exhibit the least amount of body color that a diamond in that color grade may exhibit. A trained diamond grader compares a diamond of unknown grade against the series of master stones, assessing where in the range of color the diamond resides; this process occurs in a lighting box, fitted with daylight equivalent lamps. Accurate color grading can only be performed with diamond unset, as the comparison with master
A diamond cut is a style or design guide used when shaping a diamond for polishing such as the brilliant cut. Cut does not refer to shape, but the symmetry and polish of a diamond; the cut of a diamond affects a diamond's brilliance. In order to best use a diamond gemstone's material properties, a number of different diamond cuts have been developed. A diamond cut constitutes a more or less symmetrical arrangement of facets, which together modify the shape and appearance of a diamond crystal. Diamond cutters must consider several factors, such as the shape and size of the crystal, when choosing a cut; the practical history of diamond cuts can be traced back to the Middle Ages, while their theoretical basis was not developed until the turn of the 20th century. Design creation and innovation continue to the present day: new technology—notably laser cutting and computer-aided design—has enabled the development of cuts whose complexity, optical performance, waste reduction were hitherto unthinkable.
The most popular of diamond cuts is the modern round brilliant, whose facet arrangements and proportions have been perfected by both mathematical and empirical analysis. Popular are the fancy cuts, which come in a variety of shapes, many of which were derived from the round brilliant. A diamond's cut is evaluated by trained graders, with higher grades given to stones whose symmetry and proportions most match the particular "ideal" used as a benchmark; the strictest standards are applied to the round brilliant. Different countries base their cut grading on different ideals: one may speak of the American Standard or the Scandinavian Standard, to give but two examples; the history of diamond cuts can be traced to the late Middle Ages, before which time diamonds were employed in their natural octahedral state—anhedral diamonds were not used in jewelry. The first "improvements" on nature's design involved a simple polishing of the octahedral crystal faces to create and unblemished facets, or to fashion the desired octahedral shape out of an otherwise unappealing piece of rough.
This was called the point cut and dates from the mid 14th century. By the mid 15th century, the point cut began to be improved upon: a little less than one half of the octahedron would be sawn off, creating the table cut; the importance of a culet was realised, some table-cut stones may possess one. The addition of four corner facets created the old single cut. Neither of these early cuts would reveal. At the time, diamond was valued chiefly for its adamantine superlative hardness. For this reason, colored gemstones such as ruby and sapphire were far more popular in jewelry of the era. In or around 1476, Lodewyk van Berquem, a Flemish polisher of Bruges, introduced the technique of absolute symmetry in the disposition of facets using a device of his own invention, the scaif, he cut stones in the shape known as briolette. About the middle of the 16th century, the rose or rosette was introduced in Antwerp: it consisted of triangular facets arranged in a symmetrical radiating pattern, but with the bottom of the stone left flat—essentially a crown without a pavilion.
Many large, famous Indian diamonds of old feature a rose-like cut. However, Indian "rose cuts" were far less symmetrical as their cutters had the primary interest of conserving carat weight, due to the divine status of diamond in India. In either event, the rose cut continued to evolve, with its depth and arrangements of facets being tweaked; the first brilliant cuts were introduced in the middle of the 17th century. Known as Mazarins, they had 17 facets on the crown, they are called double-cut brilliants as they are seen as a step up from old single cuts. Vincent Peruzzi, a Venetian polisher increased the number of crown facets from 17 to 33, thereby increasing the fire and brilliance of the cut gem, properties that in the Mazarin were incomparably better than in the rose, yet Peruzzi-cut diamonds, when seen nowadays, seem exceedingly dull compared to modern-cut brilliants. Because the practice of bruting had not yet been developed, these early brilliants were all rounded squares or rectangles in cross-section.
Given the general name of cushion—what are known today as old mine cuts—these were common by the early 18th century. Sometime the old European cut was developed, which had a shallower pavilion, more rounded shape, different arrangement of facets; the old European cut was the forerunner of modern brilliants and was the most advanced in use during the 19th century. Around 1900, the development of diamond saws and good jewelry lathes enabled the development of modern diamond cutting and diamond cuts, chief among them the round brilliant cut. In 1919, Marcel Tolkowsky analyzed this cut: his calculations took both brilliance and fire into consideration, creating a delicate balance between the two. Tolkowsky's calculations would serve as the basis for all future brilliant cut modifications and standards. Tolkowsky's model of the "ideal" cut is not perfect; the original mo
Facets are flat faces on geometric shapes. The organization of occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones have facets cut into them in order to improve their appearance by allowing them to reflect light. Of the hundreds of facet arrangements that have been used, the most famous is the round brilliant cut, used for diamond and many colored gemstones; this first early version of what would become the modern Brilliant Cut is said to have been devised by an Italian named Peruzzi, sometime in the late 17th century. On, the first angles for an "ideal" cut diamond were calculated by Marcel Tolkowsky in 1919. Slight modifications have been made since but angles for "ideal" cut diamonds are still similar to Tolkowsky's formula. Round brilliants cut before the advent of "ideal" angles are referred to as "Early round brilliant cut" or "Old European brilliant cut" and are considered poorly cut by today's standards, though there is still interest in them from collectors.
Other historic diamond cuts include the "Old Mine Cut", similar to early versions of the round brilliant, but has a rectangular outline, the "Rose Cut", a simple cut consisting of a flat, polished back, varying numbers of angled facets on the crown, producing a faceted dome. Sometimes a 58th facet, called a culet is cut on the bottom of the stone to help prevent chipping of the pavilion point. Earlier brilliant cuts have large culets, while modern brilliant cut diamonds lack the culet facet, or it may be present in minute size; the art of cutting a gem is an exacting procedure performed on a faceting machine. The ideal product of facet cutting is a gemstone that displays a pleasing balance of internal reflections of light known as brilliance and colorful dispersion, referred to as "fire", brightly colored flashes of reflected light known as scintillation. Transparent to translucent stones are faceted, although opaque materials may be faceted as the luster of the gem will produce appealing reflections.
Pleonaste and black diamond are examples of opaque faceted gemstones. The angles used for each facet play a crucial role in the final outcome of a gem. While the general facet arrangement of a particular gemstone cut may appear the same in any given gem material, the angles of each facet must be adjusted to maximize the optical performance; the angles used will vary based on the refractive index of the gem material. When light passes through a gemstone and strikes a polished facet, the minimum angle possible for the facet to reflect the light back into the gemstone is called the critical angle. If the ray of light strikes a surface lower than this angle, it will leave the gem material instead of reflecting through the gem as brilliance; these lost light rays are sometimes referred to as "light leakage", the effect caused by it is called "windowing" as the area will appear transparent and without brilliance. This is common in poorly cut commercial gemstones. Gemstones with higher refractive indexes make more desirable gemstones, the critical angle decreases as refractive indices increase, allowing for greater internal reflections as the light is less to escape.
This machine uses a motor-driven plate to hold a flat disk for the purpose of cutting or polishing. Diamond abrasives bonded to metal or resin are used for cutting laps, a wide variety of materials are used for polishing laps in conjunction with either fine diamond powder or oxide-based polishes. Water is used for cutting, while either oil or water is used for the polishing process; the machine uses a system called a "mast" which consists of an angle readout, height adjustment and a gear with a particular number of teeth is used as a means of setting the rotational angle. The angles of rotation are evenly divided by the number of teeth present on the gear, though many machines include additional means of adjusting the rotational angle in finer increments called a "cheater"; the stone is bonded to a rod known as a "dop" or "dop stick" and is held in place by part of the mast referred to as the "quill". The dopped stone is ground at precise angles and indexes on cutting laps of progressively finer grit, the process is repeated a final time to polish each facet.
Accurate repetition of angles in the cutting and polishing process is aided by the angle readout and index gear. The physical process of polishing is a subject of debate. One accepted theory is that the fine abrasive particles of a polishing compound produce abrasions smaller than the wavelengths of light, thus making the minute scratches invisible. Since gemstones have two sides, a device called a "transfer jig" is used to flip the stone so that each side may be cut and polished. Cleaving relies on planar weaknesses of the chemical bonds in the crystal structure of a mineral. If a sharp blow is applied at the correct angle, the stone may split cleanly apart. While cleaving is sometimes used to split uncut gemstones into smaller pieces, it is never used to produce facets. Cleaving of diamonds was once common, but as the risk of damaging a stone is too high, undesirable diamond pieces resulted; the preferred method of splitting diamonds into smaller pieces is now sawing. An older and more primitive style of faceting machine called a jamb peg machine used wooden dop sticks of precise length and a "mast" system consisting of a plate with holes placed in it.
By placing the back end of the dop into one of the many holes, the stone could
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
Carbonado known as the "black diamond", is the toughest form of natural diamond. It is an impure form of polycrystalline diamond consisting of diamond and amorphous carbon, it is found in alluvial deposits in the Central African Republic and in Brazil. Its natural colour is black or dark grey, it is more porous than other diamonds. Carbonado diamonds are pea-sized or larger porous aggregates of many tiny black crystals; the most characteristic carbonados have been found only in the Central African Republic and in Brazil, in neither place associated with kimberlite, the source of typical gem diamonds. Lead isotope analyses have been interpreted as documenting crystallization of carbonados about 3 billion years ago; the carbonados are found in younger sedimentary rocks. Mineral grains included within diamonds have been studied extensively for clues to diamond origin; some typical diamonds contain inclusions of common mantle minerals such as pyrope and forsterite, but such mantle minerals have not been observed in carbonado.
In contrast, some carbonados do contain inclusions of minerals characteristic of the Earth's crust: these inclusions do not establish formation of the diamonds in the crust, because while these obvious crystal inclusions occur in the pores that are common in carbonados, they may have been introduced after carbonado formation. Inclusions of other minerals, rare or nearly absent in the Earth's crust, are found at least incorporated in diamond, not just in pores: among such other minerals are those with compositions of Si, SiC, Fe‑Ni. No distinctive high-pressure minerals, including the hexagonal carbon polymorph, have been found as inclusions in carbonados, although such inclusions might be expected if carbonados formed by meteorite impact. Isotope studies have yielded further clues to carbonado origin; the carbon isotope value is low. Carbonado exhibits strong luminescence induced by nitrogen and by vacancies existing in the crystal lattice. Luminescence halos are present around radioactive inclusions, it is suggested that the radiation damage occurred after formation of the carbonados, an observation pertinent to the radiation hypothesis listed below.
The origin of carbonado is controversial. Some proposed hypotheses are as follows: Direct conversion of organic carbon under high-pressure conditions in the Earth's interior, the most common hypothesis for diamond formation Shock metamorphism induced by meteoritic impact at the Earth's surface Radiation-induced diamond formation by spontaneous fission of uranium and thorium Formation inside an earlier-generation giant star in our area, that long ago exploded in a supernova. An origin in interstellar space, due to the impact of an asteroid, rather than being thrown from within an exploding star. None of these hypotheses for carbonado formation had come into wide acceptance in the scientific literature by 2008. Supporters of an extraterrestrial origin of carbonados propose that their material source was a supernova which occurred at least 3.8 billion years ago. After coalescing and drifting through outer space for about one and a half billion years, a large mass fell to earth as a meteorite 2.3 billion years ago.
It fragmented during entry into the Earth's atmosphere and impacted in a region which would much split into Brazil and the Central African Republic, the only two known locations of carbonado deposits. Amsterdam Diamond Bort Korloff Noir Material properties of diamond Popigai diamonds Sergio Spirit of de Grisogono Diamond Superhard material Photo of porous carbonado at National Science Foundation Photo of glossy carbonado and article on possible extraterrestrial origins at PBS Nova Mystery Diamonds: Geoscientists Investigate Rare Carbon Formation ScienceDaily Story Diamonds From Outer Space: Geologists Discover Origin Of Earth's Mysterious Black Diamonds ScienceDaily Story