Dictionarium polygraphicum. Indigo.

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol II.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
1735
INDIGO, a drug of a deep blue colour, brought hither from the West-Indies.

It is made of the leaves of a plant, call'd by the spaniards Anil, and by us Indigo.

The method of preparing it is as follows;

When the plant has grown to a certain height, and its leaves are in a good condition, they cut down, and throw it into a kind of vat, putting to them as much water as will cover them.

These are boil'd together for the space of 24 hours; and at the top swims a scum, with all the different colours of the rainbow.

Then the water is let off into another vessel, where they agitate it, and stir it about laboriously, with five or six poles fitted for that purpose. This they do till the water becomes of a deep green, and till the grain (as they call it) forms itself; which they discover, by taking a little of it out into another vessel, and spitting in it; for if then they perceive a blueish dreg subsiding, they cease beating it. The matter then precipitates of itself, to the bottom of the vessel; and when it is well settled, they pour off the water.

After this, they takeoff the Indigo, and put it into little linnen bags, and let it drain; this done, they put it into shallow wooden boxes, and when it begins to dry, they cut it into slices, and sec them to dry and harden in the sun.

here are several sorts of Indigo, the best is that call'd Serquisse, after the name of a village where it is prepar'd.

We chuse it in flat pieces of a moderate thickness, pretty hard, clean, light enough to swim in the water, inflammable, of a fine blue colour, marked a little on the inside with silver streaks, and appearing reddish when rubb'd on the nail.

Indigo is us'd by Painters, who grind and mix it with white to make a blue colour; for without that mixture, it would paint blackish.

It is also mix'd with yellow, to make a green colour. It is also us'd by dyers.