fast red

noun, often capitalized F&R

Definition of fast red

:any of several fast red azo dyes: such as
a :a monoazo acid dye that dyes wool and silk red called also Fast Red A
b :a monoazo acid dye that dyes wool and silk claret and is used chiefly as a biological stain called also Bordeaux B, Bordeaux red, Fast Red B

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