Patent Blue V is a safer longer-lasting alternative to sulphovanillin. Also useful for some chrysocystidia i.e. Hypholoma, Stropharia & Pholiota. Please note: after staining for a few minutes, wash 2 x with water and mount in water (not KOH or NaOH as this makes the stain fade).
Patent Blue V, also called Food Blue 5, Sulphan Blue, Acid Blue 3, L-Blau 3, C-Blau 20, Patentblau V, Sky Blue, or C.I. 42051 and is a dark bluish synthetic triphenylmethane dye used as a food coloring. As a food additive, it has E number E131. It is a sodium or calcium salt of [4-(α-(4-diethylaminophenyl)-5-hydroxy- 2,4-disulfophenylmethylidene)-2,5-cyclohexadien-1-ylidene] diethylammonium hydroxide inner salt.