Blue is one of the three primary colours in the RYB colour model, as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when observing light with a dominant wavelength between approximately 450 and 495 nanometres. Most blues contain a slight mixture of other colours; azure contains some green, while ultramarine contains some violet. The clear daytime sky and the deep sea appear blue because of an optical effect known as Rayleigh scattering. An optical effect called Tyndall effect explains blue eyes. Distant objects appear more blue because of another optical effect called aerial perspective.
Sienna is an earth pigment containing iron oxide and manganese oxide. In its natural state, it is yellowish brown and is called raw sienna. When heated, it becomes a reddish brown and is called burnt sienna. It takes its name from the city-state of Siena, where it was produced 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.
Ultramarine is a deep blue color pigment which was originally made by grinding lapis lazuli into a powder. Its lengthy grinding and washing process makes the natural pigment quite valuable— roughly ten times more expensive than the stone it comes from and as expensive as gold.
A pigment is a colored substance that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compounds. Pigments of prehistoric and historic value include ochre, charcoal, and lapis lazuli.
Raman spectroscopy is a spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Raman spectroscopy is commonly used in chemistry to provide a structural fingerprint by which molecules can be identified.
Prussian blue is a dark blue pigment produced by oxidation of ferrous ferrocyanide salts. It has the chemical formula FeIII
4[FeII
(CN)
6]
3. Turnbull's blue is chemically identical, but is made from different reagents, and its slightly different color stems from different impurities and particle sizes.
Umber is a natural brown earth pigment and color that contains iron oxide and manganese oxide. In its natural form, it is called raw umber. When calcined, the color becomes warmer and it becomes known as burnt umber.
Glauconite is an iron potassium phyllosilicate mineral of characteristic green color which is very friable and has very low weathering resistance.
Verdigris is the common name for blue-green, poisonous, copper-based pigments that form a patina on copper, bronze, and brass. The technical literature is ambiguous as to its chemical composition. Some sources refer to "neutral verdigris" as copper(II) acetate monohydrate and to "blue verdigris" as Cu(CH3CO2)2·CuO·(H2O)6. Other sources describe the main copper salt in natural verdigris as Cu4SO4(OH)6 (brochantite). Still other sources describe it as basic copper carbonate, or as Cu(CH3CO2)2·(Cu 2)n where n varies from 0 to 3. In marine envirenments, the main copper salt is tribasic copper chloride . The alchemical symbol for verdigris is 🜨.
Naples yellow, also called antimony yellow, is an inorganic pigment used in paintings during the period 1700–1850. Colors range from a muted, or earthy, reddish yellow pigment to a bright light yellow. It is the chemical compound lead antimonate (Pb2Sb2O7). Also known as jaune d'antimoine, it is one of the oldest synthetic pigments. The Ancient Egyptians were known to create it.
Celadonite is a mica group mineral, a phyllosilicate of potassium, iron in both oxidation states, aluminium and hydroxide with formula K(Mg,Fe2+
)(Fe3+
,Al)[Si
4O
10](OH)
2.
Han purple and Han blue are synthetic barium copper silicate pigments developed in China and used in ancient and imperial China from the Western Zhou period until the end of the Han dynasty.
Egyptian blue, also known as calcium copper silicate (CaCuSi4O10 or CaOCuO(SiO2)4 (calcium copper tetrasilicate)) or cuprorivaite, is a pigment that was used in ancient Egypt for thousands of years. It is considered to be the first synthetic pigment. It was known to the Romans by the name caeruleum. After the Roman era, Egyptian blue fell from use and, thereafter, the manner of its creation was forgotten. In modern times, scientists have been able to analyze its chemistry and reconstruct how to make it.
Maya blue is a unique bright azure blue pigment manufactured by cultures of pre-Columbian Mesoamerica, such as the Mayans and Aztecs.
Varieties of the color green 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 green or other hue mixed with white, a shade being mixed with black. A large selection of these various colors is shown below.
High-valent iron commonly denotes compounds and intermediates in which iron is found in a formal oxidation state > 3 that show a number of bonds > 6 with a coordination number ≤ 6. The term is rather uncommon for hepta-coordinate compounds of iron. It has to be distinguished from the terms hypervalent and hypercoordinate, as high-valent iron compounds neither necessarily violate the 18-electron rule nor necessarily show coordination numbers > 6. The ferrate(VI) ion [FeO4]2− was the first structure in this class synthesized. The synthetic compounds discussed below contain highly oxidized iron in general, as the concepts are closely related.
Varieties of the color yellow 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 yellow or other hue mixed with white, a shade being mixed with black. A large selection of these various colors is shown below.
Lead-tin yellow is a yellow pigment, of historical importance in oil painting, sometimes called the "Yellow of the Old Masters" because of the frequency with which it was used by those famous painters.
Green pigments are the materials used to create the green colors seen in painting and the other arts. Most come from minerals, particularly those containing compounds of copper. Green pigments reflect the green portions of the spectrum of visible light, and absorb the others. Important green pigments in art history include Malachite and Verdigris, found in tomb paintings in Ancient Egypt, and the Green earth pigments popular in the Middle Ages. More recent greens, such as Cobalt Green, are largely synthetic, made in laboratories and factories.
Color coordinates