indigo
A blue vat dyestuff, with the formula (C
16 H 10 N 2 O
2 ), formerly derived by fermentation
of the leaves of the herbaceous shrubs Isatis
tinctoria, Polygonum tinctoria, etc., but now
manufactured from anthranilic acid (C
16 H 10 N 2 O
2 ), and used, along with wood ashes,
mainly in northern Nigeria, in the removal of hair
from goatskin. In the 19th century the natural
product was used, in conjunction with sulfuric
acid, to make a blue coloring matter for use in
the production of leather cover marbles. (130 )
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