From the late 1870s the English dye-makers had become incapable of sustaining their earlier lead in technical development, and were unable to develop markets outside the British Empire. They lacked the commitment to manufacturing adopted by the Germans, who placed great emphasis on production and quality, backed up with product testing and customer service. This was carried over to later generations of dyestuffs, whereby new discoveries suited to the needs of consumers worldwide reached the market place in the shortest possible time. The British commitment to natural indigo ensured that the factory-made blue colorant was to be another German triumph.
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).
Alizarin Yellow R | 2243-76-7 | AL210 | Spectrum Chemical
A simple and straightforward method has been proposed for quantification of residual amine in cured epoxy resin. Non-bounded triethylenetetramine was extracted from epoxy polymer and determined via spectrophotometry using alizarin chromophore. Four solvents commonly used as food simulants, namely water, 95% ethanol, 10% ethanol and 3% acetic acid were examined. Released amine induces changes in the absorption spectrum of alizarin, by decreasing the intensity of the maximum at 430 nm band and mutually increasing the 527 nm band. These changes were proportional to the amounts of amine concentration in samples. The statistical significance of obtained calibration curves was validated. Among studied solvents, the highest amine release was observed for water solution and 3% acetic acid, that is approximately 7% w/w. The maximal amount of residual amine extracted with 95% ethanol was about 1.25%, while for 10% ethanol this amount was 2%. The effect of aging of the samples and exposure to artificial sunlight were also examined. The proposed method has been proven to be fast, low cost and directly applicable for analysis of typical epoxy resins.
Pigments through the Ages - History - Madder lake (Alizarin)
The alizarin process plant also underwent considerable changes in Germany (as well as in Switzerland) during the 1870s and after. Notably, the addition of potassium chlorate prevented the production of hydrogen in the fusion step, and this eliminated the reduction of products, as well as permitting the use of lower pressures. The neglect of such technical improvements and of the process that gave the product most in demand (the violet shade) foreshadowed the end of the innovative edge by British firms during the nineteenth century.
Pigments through the Ages - History - Madder lake
The Germans had a greater commitment to the anthraquinone route, the first one developed, and which gave alizarin as the major product from the monosulfonic acid, and they soon managed to control the reaction conditions to obtain the maximum yield. Perkin, however, continued to exploit the dichloroanthracene process, which afforded mainly a mixture of two disulfonic acids, and very little mono- acid. Red shade anthrapurpurin (or isopurpurin, a trihydroxy derivative), was the main product; alizarin was as a minor component.
PDF Downloads : Oriental Journal of Chemistry
Certainly these mixtures are somewhat dull, but not any duller than the orange one gets by mixing "primary" quinacridone magenta () and "primary" cadmium yellow (), or the violet blue one gets by mixing "primary" quinacridone magenta with "primary" phthalocyanine blue (). When we compare these mixtures to single pigment violet blue, green blue (), red () or orange paints (), the "possible" and "impossible" mixtures look pretty much the same.