The structure of alpha phthalocyanine blue (PB15:3) is representative: four carbon rings linked into a flat plate by carbon and nitrogen; the metal atom (in this case, copper) bonds to two of the four inner nitrogen atoms. The green shades, which are chemically less stable, form by replacing 15 of the hydrogen atoms on the outer carbon rings with chlorine (PG7) or chlorine and bromine (PG36) atoms. The individual dye plates can form chains or polymers by linking the copper atoms to each other through intermediate oxygen atoms; these form the pigment particles. Phthalo blues and greens have been available in artists' paints since the 1950's, but have only recently gained wide use among watercolorists. (The strongly staining character of these early phthalo blue paints was discouraging.) The colors used in artists' paints range in hue from a reddish blue ( or ) to greenish blue (), cyan (), turquoise (), bluish green (), and yellowish green (PG13, ); only the metal free form (PB16, a dull greenish blue) is a true synthetic organic pigment. All shades (but especially the greens) increase in chroma and tinting strength as average goes below 0.15µm, which is achieved by finishing with acids or mechanical grinding. Phthalocyanines are indispensable pigments in the green part of the color circle: PG7 or PG36 are base ingredients for a wide range of mixtures. The natural scarcity of blue and green pigments is illustrated by the fact that phthalo blue is the most important blue pigment discovered since cobalt blue (1804) or ultramarine blue (1828); phthalo green is the most important green pigment since emerald green (1814) or viridian (1838).
Hues arise because the light incident on a surface is reflected unequally at different wavelengths. The eye combines these different wavelengths into a single hue perception. This hue can usually be matched by the color of a single wavelength of light, called the dominant wavelength of the hue, notated as the wavelength number, e.g. a pure yellow is indicated by the wavelength number Hues that do not appear in the spectrum are matched by a mixture of two wavelengths of light, one violet and one red. As these two wavelength mixtures or extraspectral hues are awkward to specify for technical reasons, they are usually denoted by the wavelength number of the hue directly opposite on the hue circle: thus an extraspectral magenta is notated by its complementary "green" wavelength,
Superceded by Prussian blue in the early 18th century, and rendered obsolete after the synthesisation of Ultramarine and the development of Cobalt Blue.
A relatively opaque white-yellow pigment, it is a form of Barium Chromate, and is also known as Lemon Yellow.
The development of the colonial natural dye industry in North America coincided with a transatlantic revolution in methods of manufacture, especially of textiles. The rapid growth of the textile industry from the end of the eighteenth century came about through the introduction of mechanized processes, improvements in bleaching, and by the mid-nineteenth century multi-color roller printing. Notably, chlorine became the bleaching agent of choice. These new processes, and the introduction of steam power, enabled rapid and large scale production, and were accompanied by unprecedented demand for dyes. This encouraged scientific studies, especially new methods for applying dyes in printing, and improved extraction processes notably in France. The Emperor Napoleon I signed a decree calling for madder dyeing on wool to be improved, and in the 1820s the newly formed Societe Industrielle de Mulhouse offered a prize for chemical knowledge about madder This led to the first isolation and analyses of alizarin and purpurin.
In a 4week study, groups of four male and four female Wistar rats were fed diets containing 0% or 5% of OSB, R10 or WSA. Animals received either: (1) diet containing annatto extract during the first 2 weeks and normal diet for the second 2 weeks; or (2) normal diet for 2 weeks followed by the diet containing annatto extract for 2 weeks. In the animals that were killed immediately after receiving annatto extract for 2 weeks, measurable amounts of yellow pigment were observed in the blood, but in animals that were killed 2 weeks after treatment with annatto extract had stopped, only trace amounts were detected. Yellow pigment was also found in the adipose tissue of animals treated with OSB and R10, but not in animals receiving WSA. Chromatographic analysis of these pigments confirmed that they were not major annatto pigments (bixin or norbixin). There was also a clear difference in the degree of discoloration of the fat in animals killed immediately after cessation of treatment, compared with that in animals killed 2 weeks after treatment had stopped, indicating that clearance of the pigment was rapid. Faeces were collected during the second week of treatment and analysed for pigment content. About 20% of the administered dose of OSB and WSA and about 55% of R10 was recovered unchanged from the faeces.
Alizarin () A coloring principle, C14H6O2(OH)2, found in madder, and now produced artificially from anthracene. It produces the Turkish reds.
average hue locations on the CIECAM aCbC hue plane at lightness 6; letters R, Y, G, B and P indicate location of Hering unique hues (red, yellow, green, blue) and Munsell purple
The diagram also shows the limitations of using conceptual colors, such as the traditional color theory "primary" colors, to explain color mixing. For example, cobalt teal blue () mixes a pure gray with both pyrrole orange () and cadmium red deep (). But pyrrole orange has a distinctly yellow component in its hue, and therefore has substantially more "yellow primary" in it than cadmium deep red. So then how can a paint with more "yellow primary" in it mix the same gray with the same green blue paint? The conceptual "primary" colors have no logical or necessary connection to the visual color of two material colors, or to the color of their physical mixture.
Those patterns occur because we live in a real world of atomic substances, and the follow the organizing patterns of chemistry and physics. These tend to produce transmission or reflectance curves in most substances that follow more regular patterns, such as the profile typical of saturated red, orange and yellow paints and filters. In addition, painters work with a very limited range of colored substances chemically pure and complex colorants, the pigments in their paints and modern colorants create a fairly predictable domain of reflectance profiles.
Imagine two idealized photographic gel (transparent) filters, designed to pass either 100% or 0% of the light at each wavelength. There are no limits on the combination of specific wavelengths we are able to filter, except that in every case one filter must make a "white" beam of light appear yellow, and the other must make a "white" light appear orange.
Each of these problems, taken separately, can create formidable problems in describing or "predicting" material color mixtures. In combination, they overcome any generalizations based on visual or conceptual colors.
The conditions of sale had been agreed on 1 October 1982, and early in the following year ICI Francolor SA was created, a wholly owned subsidiary of ICI incorporating its former sales agency, ICI France. ICI had thus inherited not only the interests of the successors to Perkin, Simpson, Maule & Nicholson, Levinstein, the Hollidays, and Morton, but also the innovative tradition established by Poirrier at Saint Denis, Paris, where in the 1860s the new alkylation of aniline process was first conducted. Not far away, at Villers Saint Paul dye making was fully computerized in 1982, while at Oissel, "red and yellow azo dyes are synthesized by a continuous process. This is believed to be the first and only one of its kind in the world."
This problem is minimized, but hardly eliminated, by limiting the application of subtractive mixing principles to manufactured colorants. Even here, the variety of materials includes light reflecting substances (such as powders, paints, dyes or inks) and light transmitting substances (such as photographic filters, stained glass or tinted liquids).