Hematite, also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of Fe
2O
3. It has the same crystal structure as corundum (Al
2O
3) and ilmenite (FeTiO
3). With this it forms a complete solid solution at temperatures above 950 °C (1,740 °F).
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH)3), and is typically associated with the corrosion of refined iron.
Sienna is an earth pigment containing iron oxide and manganese oxide. In its natural state, it is yellowish brown, and it is called raw sienna. When heated, it becomes a reddish brown, and it is called burnt sienna. It takes its name from the city-state of Siena, where it was produced more widely during the Renaissance. Along with ochre and umber, it was one of the first pigments to be used by humans, and is found in many cave paintings. Since the Renaissance, it has been one of the brown pigments most widely used by artists.
Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing and painting, brown is usually made by combining the colors orange and black. In the RGB color model used to project colors onto television screens and computer monitors, brown combines red and green.
In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+.
In chemistry, the adjective ferrous indicates a compound that contains iron(II), meaning iron in its +2 oxidation state, possibly as the divalent cation Fe2+. It is opposed to ferric, or iron(III), meaning iron in its +3 oxidation state, such as the trivalent cation Fe3+. This usage has been largely replaced by the IUPAC nomenclature, which calls for the oxidation state being indicated by Roman numerals in parentheses, such as iron(II) oxide for ferrous oxide (FeO), iron(III) oxide for ferric oxide (Fe2O3), and iron(II,III) oxide for the oxide Fe3O4 that contains both forms of iron.
Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of iron for the steel industry. Fe2O3 is readily attacked by acids. Iron(III) oxide is often called rust, since rust shares several properties and has a similar composition; however, in chemistry, rust is considered an ill-defined material, described as hydrous ferric oxide.
Vermilion is a color family and pigment most often used between antiquity and the 19th century from the powdered mineral cinnabar. It is synonymous with red orange, which often takes a modern form, but is 11% brighter.
Umber is a natural earth pigment consisting of iron oxide and manganese oxide; it has a brownish color that can vary among shades of yellow, red, and green. Umber is considered one of the oldest pigments known to humans, first seen in Ajanta Caves in 200 BC – 600 AD. Umber's advantages are its highly versatile color, warm tone, and quick drying abilities. While some sources indicate that umber's name comes from its geographic origin in Umbria, other scholars suggest that it derives from the Latin word umbra, which means "shadow". The belief that its name derives from the word for shadow is fitting, as the color helps create shadows. The color is primarily produced in Cyprus. Umber is typically mined from open pits or underground mines and ground into a fine powder that is washed to remove impurities. In the 20th century, the rise of synthetic dyes decreased the demand for natural pigments such as umber.
Venetian red is a light and warm (somewhat unsaturated) pigment that is a darker shade of red. The composition of Venetian red changed over time. Originally it consisted of natural ferric oxide (Fe2O3, partially hydrated) obtained from the red hematite. Modern versions are frequently made with synthetic red iron oxide produced via calcination of green vitriol (a.k.a. copperas) mixed with white chalk. The pigment contains up to 50% of the ferric oxide.
Viridian is a blue-green pigment, a hydrated chromium(III) oxide, of medium saturation and relatively dark in value. It is composed of a majority of green, followed by blue. The first recorded use of viridian as a color name in English was in the 1860s. Viridian takes its name from the Latin viridis, meaning "green". The pigment was first prepared in mid-19th-century Paris and remains available from several US manufacturers as prepared artists' colors in all media.
Bluing, sometimes spelled as blueing, is a passivation process in which steel is partially protected against rust using a black oxide coating. It is named after the blue-black appearance of the resulting protective finish. Bluing involves an electrochemical conversion coating resulting from an oxidizing chemical reaction with iron on the surface selectively forming magnetite, the black oxide of iron. In comparison, rust, the red oxide of iron, undergoes an extremely large volume change upon hydration; as a result, the oxide easily flakes off, causing the typical reddish rusting away of iron. Black oxide provides minimal protection against corrosion, unless also treated with a water-displacing oil to reduce wetting and galvanic action. In colloquial use, thin coatings of black oxide are often termed 'gun bluing', while heavier coatings are termed 'black oxide'. Both refer to the same chemical process for providing true gun bluing.
Varieties of the color red may differ in hue, chroma or lightness, or in two or three of these qualities. Variations in value are also called tints and shades, a tint being a red or other hue mixed with white, a shade being mixed with black. A large selection of these various colors are shown below.
Rufous is a color that may be described as reddish-brown or brownish-red, as of rust or oxidised iron. The first recorded use of rufous as a color name in English was in 1782. However, the color is also recorded earlier in 1527 as a diagnostic urine color.
Tuscan red is a shade of red that was used on some railroad cars, particularly passenger cars.
Variations of gray or grey include achromatic grayscale shades, which lie exactly between white and black, and nearby colors with low colorfulness. A selection of a number of these various colors is shown below.
Shades of brown can be produced by combining red, yellow, and black pigments, or by a combination of orange and black—illustrated in the color box. The RGB color model, that generates all colors on computer and television screens, makes brown by combining red and green light at different intensities. Brown color names are often imprecise, and some shades, such as beige, can refer to lighter rather than darker shades of yellow and red. Such colors are less saturated than colors perceived to be orange. Browns are usually described as light or dark, reddish, yellowish, or gray-brown. There are no standardized names for shades of brown; the same shade may have different names on different color lists, and sometimes one name can refer to several very different colors. The X11 color list of web colors has seventeen different shades of brown, but the complete list of browns is much longer.
Shades of black are colors that differ only slightly from pure black. These colors have a low lightness. From a photometric point of view, a color which differs slightly from black always has low relative luminance. Variations of black include what are commonly termed off-black colors, which may be considered part of a neutral color scheme, usually in interior design as a part of a background for brighter colors. Black and dark gray colors are powerful accent colors that suggest weight, dignity, formality, and solemnity.
Iron oxide red is a generic name of a ferric oxide pigment of the red color. Multiple shades based on both anhydrous Fe
2O
3 and its hydrates were known to painters since prehistory. The pigments were originally sourced from natural sources, since the 20th century they are mostly synthetic. These substances form one of the most commercially important groups of pigments, and their names sometimes reflect the location of a natural source, later transferred to the synthetic analog. Well-known examples include the Persian Gulf Oxide with 75% Fe
2O
3 and 25% silica, Spanish red with 85% of oxide, Tuscan red.
Detoxification foot baths, also known as foot detox, ionic cleansing, ionic foot bath and aqua/water detox are pseudoscientific alternative medical devices marketed as being able to remove toxins from the human body. They work by providing an electric current to an electrode array immersed in a salt water solution. When switched on, the electrodes rapidly rust in a chemical process called electrolysis which quickly turns the water brown. This reaction happens regardless of whether or not a person's feet are immersed in the water and no toxins from the human body have ever been detected in the water after use.
Color coordinates
