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94-477: Hue can typically be represented quantitatively by a single number, often corresponding to an angular position around a central or neutral point or axis on a color space coordinate diagram (such as a chromaticity diagram ) or color wheel , or by its dominant wavelength or by that of its complementary color . The other color appearance parameters are colorfulness , saturation (also known as intensity or chroma), lightness , and brightness . Usually, colors with

188-504: A 24-bit RGB model is thus limited to a range of 256×256×256 ≈ 16.7 million colors. Some implementations use 16 bits per component for 48 bits total, resulting in the same gamut with a larger number of distinct colors. This is especially important when working with wide-gamut color spaces (where most of the more common colors are located relatively close together), or when a large number of digital filtering algorithms are used consecutively. The same principle applies for any color space based on

282-746: A Cr-Cr quintuple bond (length 183.51(4) pm) has also been described. Extremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions. Chromium is the 21st most abundant element in Earth's crust with an average concentration of 100 ppm. Chromium compounds are found in the environment from the erosion of chromium-containing rocks, and can be redistributed by volcanic eruptions. Typical background concentrations of chromium in environmental media are: atmosphere <10 ng/m ; soil <500 mg/kg; vegetation <0.5 mg/kg; freshwater <10 μg/L; seawater <1 μg/L; sediment <80 mg/kg. Chromium

376-414: A change to less toxic chromium(III) compounds. The mineral crocoite (which is also lead chromate PbCrO 4 ) was used as a yellow pigment shortly after its discovery. After a synthesis method became available starting from the more abundant chromite, chrome yellow was, together with cadmium yellow , one of the most used yellow pigments. The pigment does not photodegrade, but it tends to darken due to

470-433: A color hexagon, similar to a trilinear plot described by Evans, Hanson, and Brewer, which may be used to compute hue from RGB . To place red at 0°, green at 120°, and blue at 240°, Equivalently, one may solve Preucil used a polar plot, which he termed a color circle. Using R, G, and B, one may compute hue angle using the following scheme: determine which of the six possible orderings of R, G, and B prevail, then apply

564-450: A color system with a hue was explored as early as 1830 with Philipp Otto Runge 's color sphere. The Munsell color system from the 1930s was a great step forward, as it was realized that perceptual uniformity means the color space can no longer be a sphere. As a convention, the hue for red is set to 0° for most color spaces with a hue. In opponent color spaces in which two of the axes are perceptually orthogonal to lightness, such as

658-521: A critical material during the emergency". The United States likewise considered chromium "essential for the German war industry" and made intense diplomatic efforts to keep it out of the hands of Nazi Germany . The high hardness and corrosion resistance of unalloyed chromium makes it a reliable metal for surface coating; it is still the most popular metal for sheet coating, with its above-average durability, compared to other coating metals. A layer of chromium

752-438: A formal definition—the language was not available—but there is no doubt that he had the concept. With this conceptual background, in 1853, Grassmann published a theory of how colors mix; it and its three color laws are still taught, as Grassmann's law . As noted first by Grassmann... the light set has the structure of a cone in the infinite-dimensional linear space. As a result, a quotient set (with respect to metamerism) of

846-449: A given color space, we can assign the amount of magenta color to the representation's X axis , the amount of cyan to its Y axis, and the amount of yellow to its Z axis. The resulting 3-D space provides a unique position for every possible color that can be created by combining those three pigments. Colors can be created on computer monitors with color spaces based on the RGB color model , using

940-471: A graphic or document is sometimes called tagging or embedding ; tagging, therefore, marks the absolute meaning of colors in that graphic or document. A color in one absolute color space can be converted into another absolute color space, and back again, in general; however, some color spaces may have gamut limitations, and converting colors that lie outside that gamut will not produce correct results. There are also likely to be rounding errors, especially if

1034-414: A high infrared and visible light reflectance. Chromium metal in air is passivated : it forms a thin, protective surface layer of chromium oxide with the corundum structure. Passivation can be enhanced by short contact with oxidizing acids like nitric acid . Passivated chromium is stable against acids. Passivation can be removed with a strong reducing agent that destroys the protective oxide layer on

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1128-483: A larger chromite deposit was discovered near Baltimore , United States, which quickly met the demand for tanning salts much more adequately than the crocoite that had been used previously. This made the United States the largest producer of chromium products until the year 1848, when larger deposits of chromite were uncovered near the city of Bursa , Turkey. With the development of metallurgy and chemical industries in

1222-429: A model, the variables are assigned to cylindrical coordinates . Many color spaces can be represented as three-dimensional values in this manner, but some have more, or fewer dimensions, and some, such as Pantone , cannot be represented in this way at all. Color space conversion is the translation of the representation of a color from one basis to another. This typically occurs in the context of converting an image that

1316-457: A particular combination of the color model and the mapping function, the word is often used informally to identify a color model. However, even though identifying a color space automatically identifies the associated color model, this usage is incorrect in a strict sense. For example, although several specific color spaces are based on the RGB color model , there is no such thing as the singular RGB color space . In 1802, Thomas Young postulated

1410-422: A solution of polyvinyl butyral . An 8% solution of phosphoric acid in solvent was added just before application. It was found that an easily oxidized alcohol was an essential ingredient. A thin layer of about 10–15 μm was applied, which turned from yellow to dark green when it was cured. There is still a question as to the correct mechanism. Chrome green is a mixture of Prussian blue and chrome yellow , while

1504-644: Is Δ H a b ∗ {\displaystyle \Delta H_{ab}^{*}} in CIELAB and Δ H u v ∗ {\displaystyle \Delta H_{uv}^{*}} in CIELUV. There exists some correspondence, more or less precise, between hue values and color terms (names). One approach in color science is to use traditional color terms but try to give them more precise definitions. See spectral color#Spectral color terms for names of highly saturated colors with

1598-547: Is Cr with a half-life of 27.7 days. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority less than 1 minute. Chromium also has two metastable nuclear isomers . The primary decay mode before the most abundant stable isotope, Cr, is electron capture and the primary mode after is beta decay . Cr is the radiogenic decay product of Mn (half-life 3.74 million years). Chromium isotopes are typically collocated (and compounded) with manganese isotopes. This circumstance

1692-428: Is 125 nanoohm - meters . Chromium has a high specular reflection in comparison to other transition metals. In infrared , at 425  μm , chromium has a maximum reflectance of about 72%, reducing to a minimum of 62% at 750 μm before rising again to 90% at 4000 μm. When chromium is used in stainless steel alloys and polished , the specular reflection decreases with the inclusion of additional metals, yet

1786-409: Is 8.5, which means that it can scratch samples of quartz and topaz , but can be scratched by corundum . Chromium is highly resistant to tarnishing , which makes it useful as a metal that preserves its outermost layer from corroding , unlike other metals such as copper , magnesium , and aluminium . Chromium has a melting point of 1907 °C (3465 °F), which is relatively low compared to

1880-566: Is Cr(VI). Chromium minerals as pigments came to the attention of the west in the eighteenth century. On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains which he named Siberian red lead . Though misidentified as a lead compound with selenium and iron components, the mineral was in fact crocoite with a formula of PbCrO 4 . In 1770, Peter Simon Pallas visited

1974-457: Is a "substance of very high concern" (SVHC). Gaseous chromium has a ground-state electron configuration of [ Ar ] 3d 4s . It is the first element in the periodic table whose configuration violates the Aufbau principle . Exceptions to the principle also occur later in the periodic table for elements such as copper , niobium and molybdenum . Chromium is the first element in the 3d series where

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2068-639: Is a new international digital video color space standard published by the IEC (IEC 61966-2-4). It is based on the ITU BT.601 and BT.709 standards but extends the gamut beyond the R/G/B primaries specified in those standards. HSV ( h ue, s aturation, v alue), also known as HSB (hue, saturation, b rightness) is often used by artists because it is often more natural to think about a color in terms of hue and saturation than in terms of additive or subtractive color components. HSV

2162-618: Is a specific organization of colors . In combination with color profiling supported by various physical devices, it supports reproducible representations of color – whether such representation entails an analog or a digital representation. A color space may be arbitrary, i.e. with physically realized colors assigned to a set of physical color swatches with corresponding assigned color names (including discrete numbers in – for example – the Pantone collection), or structured with mathematical rigor (as with

2256-422: Is a steely-grey, lustrous , hard, and brittle transition metal . Chromium is valued for its high corrosion resistance and hardness . A major development in steel production was the discovery that steel could be made highly resistant to corrosion and discoloration by adding metallic chromium to form stainless steel . Stainless steel and chrome plating ( electroplating with chromium) together comprise 85% of

2350-483: Is a strong oxidizing agent. Compounds of chromium(V) are rather rare; the oxidation state +5 is only realized in few compounds but are intermediates in many reactions involving oxidations by chromate. The only binary compound is the volatile chromium(V) fluoride (CrF 5 ). This red solid has a melting point of 30 °C and a boiling point of 117 °C. It can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure. The peroxochromate(V)

2444-465: Is a transformation of an RGB color space, and its components and colorimetry are relative to the RGB color space from which it was derived. HSL ( h ue, s aturation, l ightness/ l uminance), also known as HLS or HSI (hue, saturation, i ntensity) is quite similar to HSV , with "lightness" replacing "brightness". The difference is that the brightness of a pure color is equal to the brightness of white, while

2538-451: Is another example of the +5 oxidation state. Potassium peroxochromate (K 3 [Cr(O 2 ) 4 ]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures. This red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C. Compounds of chromium(IV) are slightly more common than those of chromium(V). The tetrahalides, CrF 4 , CrCl 4 , and CrBr 4 , can be produced by treating

2632-401: Is composed of four stable isotopes ; Cr, Cr, Cr and Cr, with Cr being the most abundant (83.789% natural abundance ). Cr is observationally stable , as it is theoretically capable of decaying to Ti via double electron capture with a half-life of no less than 1.3 × 10 years. Twenty-five radioisotopes have been characterized, ranging from Cr to Cr; the most stable radioisotope

2726-414: Is deposited on pretreated metallic surfaces by electroplating techniques. There are two deposition methods: thin, and thick. Thin deposition involves a layer of chromium below 1 μm thickness deposited by chrome plating , and is used for decorative surfaces. Thicker chromium layers are deposited if wear-resistant surfaces are needed. Both methods use acidic chromate or dichromate solutions. To prevent

2820-447: Is formed, which can be stabilized as an ether adduct CrO 5 ·OR 2 . Chromic acid has the hypothetical formula H 2 CrO 4 . It is a vaguely described chemical, despite many well-defined chromates and dichromates being known. The dark red chromium(VI) oxide CrO 3 , the acid anhydride of chromic acid, is sold industrially as "chromic acid". It can be produced by mixing sulfuric acid with dichromate and

2914-610: Is mined as chromite (FeCr 2 O 4 ) ore. About two-fifths of the chromite ores and concentrates in the world are produced in South Africa, about a third in Kazakhstan, while India, Russia, and Turkey are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa. Although rare, deposits of native chromium exist. The Udachnaya Pipe in Russia produces samples of

Hue - Misplaced Pages Continue

3008-468: Is quantified. The first is the simple difference between the two hue angles. The symbol for this expression of hue difference is Δ h a b {\displaystyle \Delta h_{ab}} in CIELAB and Δ h u v {\displaystyle \Delta h_{uv}} in CIELUV. The other is computed as the residual total color difference after Lightness and Chroma differences have been accounted for; its symbol

3102-430: Is represented in one color space to another color space, the goal being to make the translated image look as similar as possible to the original. The RGB color model is implemented in different ways, depending on the capabilities of the system used. The most common incarnation in general use as of 2021 is the 24- bit implementation, with 8 bits, or 256 discrete levels of color per channel . Any color space based on such

3196-464: Is sometimes referred to as absolute, though it also needs a white point specification to make it so. A popular way to make a color space like RGB into an absolute color is to define an ICC profile, which contains the attributes of the RGB. This is not the only way to express an absolute color, but it is the standard in many industries. RGB colors defined by widely accepted profiles include sRGB and Adobe RGB . The process of adding an ICC profile to

3290-604: Is stable at neutral pH . Some other notable chromium(II) compounds include chromium(II) oxide CrO , and chromium(II) sulfate CrSO 4 . Many chromium(II) carboxylates are known. The red chromium(II) acetate (Cr 2 (O 2 CCH 3 ) 4 ) is somewhat famous. It features a Cr-Cr quadruple bond . A large number of chromium(III) compounds are known, such as chromium(III) nitrate , chromium(III) acetate , and chromium(III) oxide . Chromium(III) can be obtained by dissolving elemental chromium in acids like hydrochloric acid or sulfuric acid , but it can also be formed through

3384-576: Is still high in comparison with other alloys. Between 40% and 60% of the visible spectrum is reflected from polished stainless steel. The explanation on why chromium displays such a high turnout of reflected photon waves in general, especially the 90% in infrared, can be attributed to chromium's magnetic properties. Chromium has unique magnetic properties; it is the only elemental solid that shows antiferromagnetic ordering at room temperature and below. Above 38 °C, its magnetic ordering becomes paramagnetic . The antiferromagnetic properties, which cause

3478-449: Is then used to produce alloys such as stainless steel. Pure chromium metal is produced by a different process: roasting and leaching of chromite to separate it from iron, followed by reduction with carbon and then aluminium . Trivalent chromium (Cr(III)) occurs naturally in many foods and is sold as a dietary supplement , although there is insufficient evidence that dietary chromium provides nutritional benefit to people. In 2014,

3572-523: Is used where high temperature would normally cause carburization , oxidation or corrosion . Incoloy 800 "is capable of remaining stable and maintaining its austenitic structure even after long time exposures to high temperatures". Nichrome is used as resistance wire for heating elements in things like toasters and space heaters. These uses make chromium a strategic material . Consequently, during World War II, U.S. road engineers were instructed to avoid chromium in yellow road paint, as it "may become

3666-580: Is useful in isotope geology . Manganese-chromium isotope ratios reinforce the evidence from Al and Pd concerning the early history of the Solar System . Variations in Cr/ Cr and Mn/Cr ratios from several meteorites indicate an initial Mn/ Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of Mn in differentiated planetary bodies. Hence Cr provides additional evidence for nucleosynthetic processes immediately before coalescence of

3760-578: Is usually based on a 6-piece piecewise mapping, treating the HSV cone as a hexacone , or the HSL double cone as a double hexacone. The formulae used are those in the table above. One might notice that the HSL/HSV hue "circle" do not appear to all be of the same brightness. This is a known issue of this RGB-based derivation of hue. Manufacturers of pigments use the word hue, for example, "cadmium yellow (hue)" to indicate that

3854-503: The CIELUV , CIEUVW , and CIELAB . RGB uses additive color mixing, because it describes what kind of light needs to be emitted to produce a given color. RGB stores individual values for red, green and blue. RGBA is RGB with an additional channel, alpha, to indicate transparency. Common color spaces based on the RGB model include sRGB , Adobe RGB , ProPhoto RGB , scRGB , and CIE RGB . CMYK uses subtractive color mixing used in

Hue - Misplaced Pages Continue

3948-571: The European Food Safety Authority concluded that research on dietary chromium did not justify it to be recognized as an essential nutrient . While chromium metal and Cr(III) ions are considered non-toxic, chromate and its derivatives, often called " hexavalent chromium ", is toxic and carcinogenic . According to the European Chemicals Agency (ECHA), chromium trioxide that is used in industrial electroplating processes

4042-470: The NCS System , Adobe RGB and sRGB ). A "color space" is a useful conceptual tool for understanding the color capabilities of a particular device or digital file. When trying to reproduce color on another device, color spaces can show whether shadow/highlight detail and color saturation can be retained, and by how much either will be compromised. A " color model " is an abstract mathematical model describing

4136-430: The lightness of a pure color is equal to the lightness of a medium gray. Early color spaces had two components. They largely ignored blue light because the added complexity of a 3-component process provided only a marginal increase in fidelity when compared to the jump from monochrome to 2-component color. In color science , there are two meanings of the term absolute color space : In this article, we concentrate on

4230-414: The wavelengths of light striking the retina . The relative strengths of the signals detected by the three types of cones are interpreted by the brain as a visible color. But it is not clear that they thought of colors as being points in color space. The color-space concept was likely due to Hermann Grassmann , who developed it in two stages. First, he developed the idea of vector space , which allowed

4324-445: The 3d electrons start to sink into the core; they thus contribute less to metallic bonding , and hence the melting and boiling points and the enthalpy of atomisation of chromium are lower than those of the preceding element vanadium . Chromium(VI) is a strong oxidising agent in contrast to the molybdenum (VI) and tungsten (VI) oxides. Chromium is the third hardest element after carbon ( diamond ) and boron . Its Mohs hardness

4418-481: The CIE 1976 ( L *, a *, b *) ( CIELAB ) and 1976 ( L *, u *, v *) ( CIELUV ) color spaces, hue may be computed together with chroma by converting these coordinates from rectangular form to polar form. Hue is the angular component of the polar representation, while chroma is the radial component. Specifically, in CIELAB while, analogously, in CIELUV where, atan2 is a two-argument inverse tangent. Preucil describes

4512-593: The Cr-centered Keggin anion [α-CrW 12 O 40 ] . Chromium(III) hydroxide (Cr(OH) 3 ) is amphoteric , dissolving in acidic solutions to form [Cr(H 2 O) 6 ] , and in basic solutions to form [Cr(OH) 6 ] . It is dehydrated by heating to form the green chromium(III) oxide (Cr 2 O 3 ), a stable oxide with a crystal structure identical to that of corundum . Chromium(VI) compounds are oxidants at low or neutral pH. Chromate anions ( CrO 4 ) and dichromate (Cr 2 O 7 ) anions are

4606-467: The Preucil circle agree with the hue angle computed for the Preucil hexagon at integer multiples of 30° (red, yellow, green, cyan, blue, magenta, and the colors midway between contiguous pairs) and differ by approximately 1.2° at odd integer multiples of 15° (based on the circle formula), the maximal divergence between the two. The process of converting an RGB color into an HSL color space or HSV color space

4700-826: The Solar System. Cr has been posited as a proxy for atmospheric oxygen concentration. Chromium is a member of group 6 , of the transition metals . The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist. Many Cr(0) complexes are known. Bis(benzene)chromium and chromium hexacarbonyl are highlights in organochromium chemistry . Chromium(II) compounds are uncommon, in part because they readily oxidize to chromium(III) derivatives in air. Water-stable chromium(II) chloride CrCl 2 that can be made by reducing chromium(III) chloride with zinc. The resulting bright blue solution created from dissolving chromium(II) chloride

4794-555: The Western world, the need for chromium increased. Chromium is also famous for its reflective, metallic luster when polished. It is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by electroplating . Chromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924. Approximately 28.8 million metric tons (Mt) of marketable chromite ore

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4888-474: The additive primary colors ( red , green , and blue ). A three-dimensional representation would assign each of the three colors to the X, Y, and Z axes. Colors generated on a given monitor will be limited by the reproduction medium, such as the phosphor (in a CRT monitor ) or filters and backlight ( LCD monitor). Another way of creating colors on a monitor is with an HSL or HSV color model, based on hue , saturation , brightness (value/lightness). With such

4982-486: The algebraic representation of geometric concepts in n -dimensional space . Fearnley-Sander (1979) describes Grassmann's foundation of linear algebra as follows: The definition of a linear space (vector space)... became widely known around 1920, when Hermann Weyl and others published formal definitions. In fact, such a definition had been given thirty years previously by Peano , who was thoroughly acquainted with Grassmann's mathematical work. Grassmann did not put down

5076-446: The chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method. Because of environmental and health regulations on chromates, alternative coating methods are under development. Chromic acid anodizing (or Type I anodizing) of aluminium is another electrochemical process that does not lead to the deposition of chromium, but uses chromic acid as an electrolyte in

5170-458: The chromium atoms to temporarily ionize and bond with themselves, are present because the body-centric cubic's magnetic properties are disproportionate to the lattice periodicity . This is due to the magnetic moments at the cube's corners and the unequal, but antiparallel, cube centers. From here, the frequency-dependent relative permittivity of chromium, deriving from Maxwell's equations and chromium's antiferromagnetism , leaves chromium with

5264-719: The color. It is similar to the YUV scheme used in most video capture systems and in PAL ( Australia , Europe , except France , which uses SECAM ) television, except that the YIQ color space is rotated 33° with respect to the YUV color space and the color axes are swapped. The YDbDr scheme used by SECAM television is rotated in another way. YPbPr is a scaled version of YUV. It is most commonly seen in its digital form, YCbCr , used widely in video and image compression schemes such as MPEG and JPEG . xvYCC

5358-642: The commercial use. Chromium is also greatly valued as a metal that is able to be highly polished while resisting tarnishing . Polished chromium reflects almost 70% of the visible spectrum , and almost 90% of infrared light . The name of the element is derived from the Greek word χρῶμα, chrōma , meaning color , because many chromium compounds are intensely colored. Industrial production of chromium proceeds from chromite ore (mostly FeCr 2 O 4 ) to produce ferrochromium , an iron-chromium alloy, by means of aluminothermic or silicothermic reactions . Ferrochromium

5452-410: The conversion between them should maintain the same color. However, in general, converting between two non-absolute color spaces (for example, RGB to CMYK ) or between absolute and non-absolute color spaces (for example, RGB to L*a*b*) is almost a meaningless concept. A different method of defining absolute color spaces is familiar to many consumers as the swatch card, used to select paint, fabrics, and

5546-409: The coordinates of the color in question, until it intersects the spectral locus . The wavelength at which the line intersects the spectrum locus is identified as the color's dominant wavelength if the point is on the same side of the white point as the spectral locus, and as the color's complementary wavelength if the point is on the opposite side. There are two main ways in which hue difference

5640-445: The deep shade of red pigment chrome red , which is simply lead chromate with lead(II) hydroxide (PbCrO 4 ·Pb(OH) 2 ). A very important chromate pigment, which was used widely in metal primer formulations, was zinc chromate, now replaced by zinc phosphate. A wash primer was formulated to replace the dangerous practice of pre-treating aluminium aircraft bodies with a phosphoric acid solution. This used zinc tetroxychromate dispersed in

5734-465: The dot gain or transfer function for each ink and thus change the appearance). YIQ was formerly used in NTSC ( North America , Japan and elsewhere) television broadcasts for historical reasons. This system stores a luma value roughly analogous to (and sometimes incorrectly identified as) luminance , along with two chroma values as approximate representations of the relative amounts of blue and red in

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5828-419: The energy-consuming change in oxidation state, the use of chromium(III) sulfate is under development; for most applications of chromium, the previously established process is used. In the chromate conversion coating process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc, and cadmium. This passivation and the self-healing properties of

5922-477: The existence of three types of photoreceptors (now known as cone cells ) in the eye, each of which was sensitive to a particular range of visible light. Hermann von Helmholtz developed the Young–Helmholtz theory further in 1850: that the three types of cone photoreceptors could be classified as short-preferring ( blue ), middle-preferring ( green ), and long-preferring ( red ), according to their response to

6016-535: The formation of chromium(III) oxide. It has a strong color, and was used for school buses in the United States and for the postal services (for example, the Deutsche Post ) in Europe. The use of chrome yellow has since declined due to environmental and safety concerns and was replaced by organic pigments or other alternatives that are free from lead and chromium. Other pigments that are based around chromium are, for example,

6110-515: The formation of discrete, stable, metal, carbide particles at the grain boundaries. For example, Inconel 718 contains 18.6% chromium. Because of the excellent high-temperature properties of these nickel superalloys , they are used in jet engines and gas turbines in lieu of common structural materials. ASTM B163 relies on chromium for condenser and heat-exchanger tubes, while castings with high strength at elevated temperatures that contain chromium are standardised with ASTM A567. AISI type 332

6204-474: The formula given in the table below. In each case the formula contains the fraction M − L H − L {\displaystyle {\frac {M-L}{H-L}}} , where H is the highest of R, G, and B; L is the lowest, and M is the mid one between the other two. This is referred to as the "Preucil hue error" and was used in the computation of mask strength in photomechanical color reproduction. Hue angles computed for

6298-491: The hue from ≈ 0° (red) up to ≈ 275° (violet), and line of purples#Table of highly-saturated purple colors for color terms of the remaining part of the color wheel. Alternative approach is to use a systematic notation. It can be a standard angle notation for certain color model such as HSL/HSV mentioned above, CIELUV , or CIECAM02 . Alphanumeric notations such as of Munsell color system , NCS , and Pantone Matching System are also used. Color space A color space

6392-496: The insoluble iron oxide. The chromate is converted by sulfuric acid into the dichromate. The dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium. The creation of metal alloys account for 85% of the available chromium's usage. The remainder of chromium is used in the chemical , refractory , and foundry industries. The strengthening effect of forming stable metal carbides at grain boundaries, and

6486-455: The light cone inherits the conical structure, which allows color to be represented as a convex cone in the 3- D linear space, which is referred to as the color cone. Colors can be created in printing with color spaces based on the CMYK color model , using the subtractive primary colors of pigment ( c yan , m agenta , y ellow , and blac k ). To create a three-dimensional representation of

6580-498: The like. This is a way of agreeing a color between two parties. A more standardized method of defining absolute colors is the Pantone Matching System , a proprietary system that includes swatch cards and recipes that commercial printers can use to make inks that are a particular color. Chromium Chromium is a chemical element ; it has symbol Cr and atomic number 24. It is the first element in group 6 . It

6674-526: The majority of transition metals. However, it still has the second highest melting point out of all the period 4 elements , being topped by vanadium by 3 °C (5 °F) at 1910 °C (3470 °F). The boiling point of 2671 °C (4840 °F), however, is comparatively lower, having the fourth lowest boiling point out of the Period 4 transition metals alone behind copper , manganese and zinc . The electrical resistivity of chromium at 20 °C

6768-428: The metal. Chromium metal treated in this way readily dissolves in weak acids. The surface chromia Cr 2 O 3 scale, is adherent to the metal. In contrast, iron forms a more porous oxide which is weak and flakes easily and exposes fresh metal to the air, causing continued rusting . At room temperature, the chromia scale is a few atomic layers thick, growing in thickness by outward diffusion of metal ions across

6862-426: The native metal. This mine is a kimberlite pipe, rich in diamonds , and the reducing environment helped produce both elemental chromium and diamonds. The relation between Cr(III) and Cr(VI) strongly depends on pH and oxidative properties of the location. In most cases, Cr(III) is the dominating species, but in some areas, the ground water can contain up to 39 μg/L of total chromium, of which 30 μg/L

6956-405: The original pigmentation ingredient, often toxic, has been replaced by safer (or cheaper) alternatives whilst retaining the hue of the original. Replacements are often used for chromium , cadmium and alizarin . Dominant wavelength (or sometimes equivalent wavelength) is a physical analog to the perceptual attribute hue. On a chromaticity diagram , a line is drawn from a white point through

7050-643: The oxidative roasting of chromite ore with sodium carbonate . The change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of potassium chromate . At yet lower pH values, further condensation to more complex oxyanions of chromium is possible. Both the chromate and dichromate anions are strong oxidizing reagents at low pH: They are, however, only moderately oxidizing at high pH: Chromium(VI) compounds in solution can be detected by adding an acidic hydrogen peroxide solution. The unstable dark blue chromium(VI) peroxide (CrO 5 )

7144-446: The oxide in a charcoal oven, for which he is credited as the one who truly discovered the element. Vauquelin was also able to detect traces of chromium in precious gemstones , such as ruby and emerald . During the nineteenth century, chromium was primarily used not only as a component of paints, but in tanning salts as well. For quite some time, the crocoite found in Russia was the main source for such tanning materials. In 1827,

7238-456: The pale green [CrCl(H 2 O) 5 ]Cl 2 and violet [Cr(H 2 O) 6 ]Cl 3 . If anhydrous violet chromium(III) chloride is dissolved in water, the violet solution turns green after some time as the chloride in the inner coordination sphere is replaced by water. This kind of reaction is also observed with solutions of chrome alum and other water-soluble chromium(III) salts. A tetrahedral coordination of chromium(III) has been reported for

7332-558: The popular range of only 256 distinct values per component ( 8-bit color ) is used. One part of the definition of an absolute color space is the viewing conditions. The same color, viewed under different natural or artificial lighting conditions, will look different. Those involved professionally with color matching may use viewing rooms, lit by standardized lighting. Occasionally, there are precise rules for converting between non-absolute color spaces. For example, HSL and HSV spaces are defined as mappings of RGB. Both are non-absolute, but

7426-415: The principal ions at this oxidation state. They exist at an equilibrium, determined by pH: Chromium(VI) oxyhalides are known also and include chromyl fluoride (CrO 2 F 2 ) and chromyl chloride ( CrO 2 Cl 2 ). However, despite several erroneous claims, chromium hexafluoride (as well as all higher hexahalides) remains unknown, as of 2020. Sodium chromate is produced industrially by

7520-463: The printing process, because it describes what kind of inks need to be applied so the light reflected from the substrate and through the inks produces a given color. One starts with a white substrate (canvas, page, etc.), and uses ink to subtract color from white to create an image. CMYK stores ink values for cyan, magenta, yellow and black. There are many CMYK color spaces for different sets of inks, substrates, and press characteristics (which change

7614-423: The production of pure chromium, the iron must be separated from the chromium in a two step roasting and leaching process. The chromite ore is heated with a mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms the stable Fe 2 O 3 . The subsequent leaching at higher elevated temperatures dissolves the chromates and leaves

7708-429: The reduction of chromium(VI) by cytochrome c7 . The Cr ion has a similar radius (63  pm ) to Al (radius 50 pm), and they can replace each other in some compounds, such as in chrome alum and alum . Chromium(III) tends to form octahedral complexes. Commercially available chromium(III) chloride hydrate is the dark green complex [CrCl 2 (H 2 O) 4 ]Cl. Closely related compounds are

7802-504: The reference color space a definite "footprint", known as a gamut , and for a given color model, this defines a color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB color model. When defining a color space, the usual reference standard is the CIELAB or CIEXYZ color spaces, which were specifically designed to encompass all colors the average human can see. Since "color space" identifies

7896-428: The rest of about 18% of the world production. The two main products of chromium ore refining are ferrochromium and metallic chromium. For those products the ore smelter process differs considerably. For the production of ferrochromium, the chromite ore (FeCr 2 O 4 ) is reduced in large scale in electric arc furnace or in smaller smelters with either aluminium or silicon in an aluminothermic reaction . For

7990-467: The same color model, but implemented at different bit depths . CIE 1931 XYZ color space was one of the first attempts to produce a color space based on measurements of human color perception (earlier efforts were by James Clerk Maxwell , König & Dieterici, and Abney at Imperial College ) and it is the basis for almost all other color spaces. The CIERGB color space is a linearly-related companion of CIE XYZ. Additional derivatives of CIE XYZ include

8084-448: The same hue are distinguished with adjectives referring to their lightness or colorfulness - for example: "light blue", " pastel blue", "vivid blue", and "cobalt blue". Exceptions include brown , which is a dark orange . In painting , a hue is a pure pigment —one without tint or shade (added white or black pigment, respectively). The human brain first processes hues in areas in the extended V4 called globs . The concept of

8178-600: The same site as Lehmann and found a red lead mineral that was discovered to possess useful properties as a pigment in paints . After Pallas, the use of Siberian red lead as a paint pigment began to develop rapidly throughout the region. Crocoite would be the principal source of chromium in pigments until the discovery of chromite many years later. In 1794, Louis Nicolas Vauquelin received samples of crocoite ore . He produced chromium trioxide (CrO 3 ) by mixing crocoite with hydrochloric acid . In 1797, Vauquelin discovered that he could isolate metallic chromium by heating

8272-442: The scale. Above 950 °C volatile chromium trioxide CrO 3 forms from the chromia scale, limiting the scale thickness and oxidation protection. Chromium, unlike iron and nickel, does not suffer from hydrogen embrittlement . However, it does suffer from nitrogen embrittlement , reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts. Naturally occurring chromium

8366-483: The second definition. CIEXYZ , sRGB , and ICtCp are examples of absolute color spaces, as opposed to a generic RGB color space . A non-absolute color space can be made absolute by defining its relationship to absolute colorimetric quantities. For instance, if the red, green, and blue colors in a monitor are measured exactly, together with other properties of the monitor, then RGB values on that monitor can be considered as absolute. The CIE 1976 L*, a*, b* color space

8460-414: The solution. During anodization, an oxide layer is formed on the aluminium. The use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers. The high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium, or at least

8554-422: The strong increase in corrosion resistance made chromium an important alloying material for steel. High-speed tool steels contain 3–5% chromium. Stainless steel , the primary corrosion-resistant metal alloy, is formed when chromium is introduced to iron in concentrations above 11%. For stainless steel's formation, ferrochromium is added to the molten iron. Also, nickel-based alloys have increased strength due to

8648-491: The trihalides ( CrX 3 ) with the corresponding halogen at elevated temperatures. Such compounds are susceptible to disproportionation reactions and are not stable in water. Organic compounds containing Cr(IV) state such as chromium tetra t -butoxide are also known. Most chromium(I) compounds are obtained solely by oxidation of electron-rich, octahedral chromium(0) complexes. Other chromium(I) complexes contain cyclopentadienyl ligands. As verified by X-ray diffraction ,

8742-416: The way colors can be represented as tuples of numbers (e.g. triples in RGB or quadruples in CMYK ); however, a color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with no connection to any globally understood system of color interpretation. Adding a specific mapping function between a color model and a reference color space establishes within

8836-448: Was produced in 2013, and converted into 7.5 Mt of ferrochromium. According to John F. Papp, writing for the USGS, "Ferrochromium is the leading end use of chromite ore, [and] stainless steel is the leading end use of ferrochromium." The largest producers of chromium ore in 2013 have been South Africa (48%), Kazakhstan (13%), Turkey (11%), and India (10%), with several other countries producing

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