archil

Hydrochloric acid turns ammoniacal cochineal pink, but merely discolours the red made from archil.

Instead of archil, any red or orange azo dyestuff may be used, preferably bordeaux.

It is however not improbable that they at first made lacmus of them, as their dye approaches very near to that of archil.

A less fast color is obtained with archil, indigo carmine and picric acid.