Production
Carmine may be prepared from cochineal, by boiling dried insects in water to extract the carminic acid and then treating the clear solution with alum. Other common substances such as cream of tartar, stannous chloride, or potassium hydrogen oxalate can also be used to effect the precipitation, but aluminum is needed for the color. Use of these chemicals causes the coloring and animal matters present in the liquid to be precipitated to give a lake pigment. Aluminum from the alum gives the traditional crimson color to carminic acid precipitates, which are called carmine lakes or crimson lakes. This color is degraded by the presence of iron salts. Addition of lime (calcium) can give carminic acid lakes a purple cast.
Other methods for the production of carmine dye are in use, in which egg white, fish glue, or gelatine is sometimes added before the precipitation.
The carminic acid used to produce the pigment can also be extracted from various microbes engineered for the purpose. Microbes are dissolved in a containment structure separate from their cultivation vats, and then allowed to settle out. The liquid and suspended carminic acid is then siphoned off, and metal salts are then added to give a lake pigment in a procedure that is mostly identical to the procedure for acid extracted from insects.
The quality of carmine is affected by the temperature and the degree of illumination during its preparation, sunlight being requisite for the production of a brilliant hue. It also differs according to the amount of alumina present in it. It is sometimes adulterated with cinnabar, starch and other materials; from these, the carmine can be separated by dissolving it in ammonia. Good carmine should crumble readily between the fingers when dry.
Carmine can be used as a staining agent in microbiology, as a Best's carmine to stain glycogen, mucicarmine to stain acidic mucopolysaccharides, and carmalum to stain cell nuclei. In these applications, it is applied together with a mordant, usually an Al(III) salt.
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