Ponceau

PONCEAU, a series of aniline azo dyes (acidic, basic, and neutral), Ponceau 2G, Crystal Ponceau, Ponceau R-4R, Ponceau S extra, Fett Ponceau, Ponceau 3RB, 4RB, 6RB. Of this series, the most commonly used dye is Fett Ponceau, or scarlet red (azo-ortho-toluol-azo-beta-naphthol), a neutral azo dye which is a red-brown powder, insoluble in water, acids, alkalis, and glycerin, soluble in alcohol, better still in chloroform, as well as in neutral fats, fatty acids, liquid and melted paraffin. According to the reports of Michaelis and Herxheimer, Fett Ponceau is preferable to Sudan III, as it stains fat more completely and intensely. For staining fat, a saturated solution in 60-70% alcohol is used; thin films or sections obtained on a freezing microtome (after formalin fixation) are placed in the staining solution (from 1/1 hour to several days), then washed in weak alcohol and mounted in glycerin or glycerin-gelatin. Staining is successful only in the presence of liquid fat; solid fats (palmitin, stearin) are stained only in an incubator at the appropriate temperature.