Blue Coloring Materials

Common name Chemical identity Starting date Comments 

Azurite (blue) Basic copper carbonate, 2CuC03Cu(0H)2 From prehistoric times Most important in wall paintings in the East known in ancient Egypt 

Carmine Cochineal carminic acid, a Kermes— Kermes—one of the oldest 

Charcoal (black) Elemental carbon From prehistoric times Also called carbon black produced by dry distillation of wood in a closed vessel 

Cinnabar (Vermilion, Mercury(II) sulfide, HgS From antiquity One of the oldest known synthetic pigments 

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Nile Blue is used as a 0.01 to 0.1 %W/V aqueous solution and is simply added to or mixed with the substrate. The active component of the dye is actually a minor contaminant of the solution, not the blue-colored material [31]. The preparations are viewed with 450-490 nm excitation (an FTTC filter set. Figure 6). Emulsion stability is sometimes an issue in the presence of the cationic blue component of Nile Blue. In this case we use Nile Red, the pure form of this colorant. Nile Red solution is made fresh from a stock solution (0.1%W/V in acetone). This stock is added dropwise to water until a moderate blue color is seen and the solution is used immediately (it deteriorates quickly). For either colorant, the active molecule is fluorescent only when it is in a suitably hydrophobic environment. This usually means neutral lipid droplets [31] but other sites (aggregates of surfactants, the center of casein micelles, cutin plates in some seeds) are possibilities. 

Prussian blue, K[Fe Fe (CN)6], was the first mixed valent inorganic complex to be synthesized. This deep blue colored material, first recorded in 1704, has been used in pigments and inks since early in the eighteenth century. Other double... 

Both, the spiro compound XVIII and the diarylethene XX exhibit nearly no color. Exposure with UV light converts XVIII and XX into the deep blue colored materials XIX and XXI [DUR 03], respectively. This isomerization presumably occurs with the heat provided by the laser. Otherwise, the addition of both these chromophores would not be explainable. 

Some treatments are practiced so widely that untreated material is essentially unknown ia the jewelry trade. The heating of pale Fe-containing chalcedony to produce red-brown carnelian is one of these. Another example iavolves turquoise where the treated material is far superior ia color stabiUty. Such treatments have traditionally not been disclosed. Almost all blue sapphire on the market has been heat treated, but it is not possible to distinguish whether it was near-colorless comndum containing Fe and Ti before treatment, or whether it had already been blue and was only treated ia an attempt at marginal improvement. The irradiation of colorless topa2 to produce a blue color more iatense than any occurring naturally is, however, self-evident, and treatments used on diamond are always disclosed. 

Printers use colored materials, eg, inks (qv), that absorb or subtract regions of the visible spectmm from white light. Subtractive color is usually represented by the three printer s primaries cyan, magenta, and yeUow (CMY). Cyan absorbs red light, magenta absorbs green, and yeUow absorbs blue light. 

Color from Vibrations and Rotations. Vibrational excitation states occur in H2O molecules in water. The three fundamental frequencies occur in the infrared at more than 2500 nm, but combinations and overtones of these extend with very weak intensities just into the red end of the visible and cause the blue color of water and of ice when viewed in bulk (any green component present derives from algae, etc). This phenomenon is normally seen only in H2O, where the lightest atom H and very strong hydrogen bonding combine to move the fundamental vibrations closer to the visible than in any other material. 

The stmcture of the blue material was not elucidated until 1934, when it was shown to be the iron complex of (67). The new material was christened phthalocyanine [574-93-6] reflecting both its origin from phthaUc anhydride and its beautihil blue color (like cyanine dyes). A year later the stmcture was confirmed by one of the first uses of x-ray crystallography. 

Native, multi-subunit KLH also should not be frozen. Freeze-thaw effects cause extensive denaturation and result in considerable amounts of insoluble material. Commercial preparations of native KLH are typically freeze-dried solids that no longer fully dissolve in aqueous buffers and do not display the protein s typical blue color due to loss of chelated copper. The partial denatured state of these products often makes conjugation reactions difficult. 

The Folin-Denis assay is used as a procedure for the quantification of total phenolics in plant materials, food, and beverages. Reduction of phosphomolybdic-phosphotungstic acid (Folin-Denis reagent) to a blue-colored complex in an alkaline solution occurs in the presence of phenolic compounds (Folin and Denis 1912). 

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