When the plant is perfectly saturated, the
cochineal is scraped off with great care. The plants are not very
valuable for the first year, but they may be estimated as yielding after
the second year, from a dollar and a half profit on each plant."
The insect is famous for the fine scarlet dye which it communicates to
wool and silk. The females yield the best colour, and are in number to
the males as three hundred to one. Cochineal was at first supposed to
be a grain, which name it retains by way of eminence among dyers, but
naturalists soon discovered it to be an insect. Its present importance
in dyeing is an excellent illustration of chemistry applied to the arts;
for long after its introduction, it gave but a dull kind of _crimson_,
till a chemist named Kuster, who settled at Bow, near London, about the
middle of the sixteenth century, discovered the use of the solution of
tin, and the means of preparing with it and cochineal, a durable and
beautiful scarlet.
Fine cochineal, which has been well dried and properly kept, ought to
be of a grey colour inclining to purple. The grey is owing to a powder
which covers it naturally, a part of which it still retains; the purple
tinge proceeds from the colour extracted by the water in which it has
been killed. Cochineal will keep a long time in a dry place. Hellot
says, that he tried some one hundred and thirty years old, and found it
produce the same effect as new.
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