Red Coloring Materials

Another important organic red color that has served since ancient times for dyeing textile materials is madder. This colorant is derived from the roots of Rubia tinctorum and other plants in the Rubiaceae family it consists of a mixture of alizarin, purpurin, and pseudopurpurin, and thus one might expect that the natural product would yield a variety of shades. It was described by Strabo, Dioscorides, Pliny the Elder, and in the Tahnud. It has been identified on Egyptian textiles as early as 1300 BCE and in six paint pots of Greco-Roman origin that are now in the British Museum. In addition, textiles dyed with madder were sold at the St. Denis 

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Main signs symptoms Diarrhea with abdominal pain, tenesmus, burning heat around the anus, diarrhea containing pus and blood with more red colored material and less white colored material, thirst with a desire to drink chilled water, a red tongue with yellow coating, and a wiry, rapid pulse... 

Let us look at some typical ceramic color stains. Red stains can be obtained with iron oxide, chromium-alumina combination, copper compound, or cadmium sele-nide. The red iron ore hematite is iron oxide (FejOj, di-iron trioxide). Iron oxide is perhaps one of the oldest red coloring materials for ceramics. The tint of the red color produced by iron oxide depends on how it is produced particularly critical are the temperature of calcination (to be explained below) and the grain size. Larger grain sizes reduce the brightness of red color. 

Bromine ttifluoride is commercially available at a minimum purity of 98% (108). Free Br2 is maintained at less than 2%. Other minor impurities are HF and BrF. Free Br2 content estimates are based on color, with material containing less than 0.5% Br2 having a straw color, and ca 2% Br2 an amber-red color. Fluoride content can be obtained by controlled hydrolysis of a sample and standard analysis for fluorine content. Bromine ttifluoride is too high boiling and reactive for gas chromatographic analysis. It is shipped as a Hquid in steel cylinders in quantities of 91 kg or less. The cylinders are fitted with either a valve or plug to faciUtate insertion of a dip tube. Bromine ttifluoride is classified as an oxidizer and poison by DOT. 

The greatest industrial consumption of monobasic aluminum acetate has been as a solution in the preparation of red color lakes for the dyeing of cotton. Formation of a water-resistant coating on fabrics, paper, leather, or other materials is also an important appHcation. In this process, for example, cloth is dipped into a solution of water-soluble soap, then into the aluminum salt solution, forming an insoluble, water-resistant aluminum soap coating on the fiber surfaces (10). 

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. 

Raw lac is first treated to remove water-soluble carbohydrates and the dye that gives lac its red color. Also removed are woody materials, insect bodies, and trash. It is further refined by either hot filtration or a solvent process. In the heat process, the dried, refined lac is filtered molten through cloth or wine screens to produce the standard grades of orange shellac. In the solvent process, lac is dissolved and refluxed in alcohol solvents, filtered to remove dirt and impurities, and concentrated by evaporation. The lac can be further decolori2ed in this process to produce very pale grades. Bleached shellac is prepared by treatment with dilute sodium hypochlorite and coalesced into slabs. 

Other Uses. Photochromic glass contains silver chloride (80) and silver molybdate [13765-74-7] (81) (see Chromogenic materials). An apparatus coated with silver nitrate has been described for the detection of rain or snow (82). Treatment with silver-thiosulfate complex has been reported as dramatically increasing the post-harvest life of cut carnations (83). Silver sulfate has been used in the electrolytic coloring of aluminum (84). Silver sulfate also imparts a yellowish red color to glass bulbs (85). 

Although this material is suitable for most purposes, it may be purified further in the following manner. It is dissolved by heating in a solution of 2 g. of stannous chloride and 2 cc. of concentrated hydrochloric acid in i 1. of water, and the hot solution is clarified by filtration through a 5-mm. mat of decolorizing carbon (Note g). The yellow or red color which may develop disappears on reheating to the boiling point. After the addition of 100 cc. of concentrated hydrochloric acid the solution is allowed to cool in an ice bath, treated with a second roo cc. of acid, cooled to 0°, and collected and washed as befor The ciystalline product is colorless, ash-free, and of analytical purity. The loss in the crystallization of an 80-g. lot amounts to 5-10 g. (6-12 per cent). 

Nakamura, Takagi and Ueno have also utilized 4 -nitrobenzo-l 5-crown-5 as a starting material Their goal was the formation of a colored crown which could be utilized in transport studies. They have prepared 4 -picrylaminobenzo-l 5-crown-5 for this purpose in the following way. 4 -Nitrobenzo-l 5-crown-5 was hydrogenated and then picryl chloride was added. Nucleophilic aromatic substitution apparently ensued (deep red color) and the product was th n isolated by standard techniques as a yellow solid (mp 155°, max 395 nm) in 72% yield as shown in Eq. (3.17). 

There are also methods based on the detection of aldehydic substances, for the typical odor and flavor of rancidity seem to be associated with the liberation of aldehydic materials during the oxidative deterioration. The Kreis test (18), perhaps the best known of these methods, consists of treating the fat with concentrated hydrochloric acid and a solution of phloroglucinol. The red color formed is attributed to a condensation product of epihydrin aldehyde with phloroglucinol. Historically, the chief difficulty with this method has been that fats which are not rancid will often give a positive Kreis test. It has been shown that if this test is quantitatively correlated with the induction period... 

The He-Ne laser has a stable, narrow-beam output at 632.8 nm in the red region. This type of laser typically has short term peak-to-peak fluctuation of less than 1%. Its long wavelength enables the studies of colorless materials and colored red-transmitting materials. The 632.8 nm line has a maximum output about 80 mW. 

Carotenoid-rich extracts can be used for coloring purposes and serve as good sources of bioactive compounds. Breeding or genetic manipulation can substantially increase the carotenoid contents of plants, resulting in carotenoid-rich foods that can be applied either as direct sonrces of nutrients or as raw materials for extracting natnral yellow to red colorants. 

After evaluating all the materials provided by Ascolor Biotech, the Codex Ali-mentarius Commission (Rotterdam meeting, March 2002) stated, There will not be any objections to use the red coloring matter Arpink Red in ... 

It appears that the greatest value of the Schechter-Haller method applied to the determination of methoxychlor is in the analysis of materials whose previous spray history is unknown. The production of a red color in such analysis indicates the possibility of the existence of methoxychlor, and warrants a further specific test. 

Most materials exhibit specific colors because they absorb certain wavelengths (colors) from white, ordinary light. A red object exposed to white light, for example, appears red because atoms on its surface absorb all the other colors in the beam and reflect only red. If transparent materials contain coloring materials, such as dyes or pigments, they absorb the characteristic color of the coloring material. 

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