The lichens thus treated acquire gradually a deep
purple colour, and form the products called "cudbear." This dye works
best in a neutral bath, but it will do what not many dyes will, namely,
dye in either a slightly alkaline or slightly acid bath as well. Orchil
is not applicable in cotton dyeing. Being a substantive colour no
mordants are needed in dyeing silk and wool with it. The colour produced
on wool and silk is a bright magenta-red with bluish shade.
Litmus is also obtained from the same lichens as yield orchil. It is not
used in dyeing, and is a violet-blue colouring matter when neither acid
nor alkaline, but neutral as it is termed. It turns red with only a
trace of acid, and blue with the least trace of alkali, and so forms a
very delicate reagent when pieces of paper are soaked with it, and
dipped into the liquids to be tested.
Safflower: This vegetable dyeing material, for producing pink colours on
cotton without the aid of a mordant, consists of the petals of the
flower of _carthamus tinctorius_.
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