Dictionarium polygraphicum. Of preparing colours. To wash colours. Steeping of colours.

Dictionarium Polygraphicum:
Or, The Whole Body of Arts Regularly Digested.
Vol I.
London: Printed for C. Hitch and C. Davis in Pater-noster Row, and S. Austen in St. Paul's Church Yard. MDCCXXXV.
1735
To WASH COLOURS.
Put the Colour into a glaz'd vessel, and put fair water to it plentifully, wash it well, and decant (after a while) the water; do this fix or seven times; at last put the water (being just troubled) into another glaz'd vessel, leaving the dregs at the bottom; then into this second vessel put more fair water, washing it as before, till the water (being settled) be clear and the Colour remain fine at the bottom.
Before you take the Colour out of the vessel, spread it very thin, about the sides thereof, and when it is dry, some of it will fall to the bottom, which keep by itself; but the remainder which slicks to the sides of the bason is the best of all, which with a feather, sirike off from the sides of the vessel, for it will be finer than any flour.

STEEPING of COLOURS.
Take a quantity of the colour, and put it into a shell, and fill the shell with fair water, to which add some fine powder of allum, to raise the Colour; let it thus steep a day and night, and you will have a good colour.
Where note, saffron steep'd in vinegar gives a good Colour, and the Venice berries in fair water and a little allum, or a drop or two of oil of vitriol makes a fair yellow.
But some Colours are to be boil'd, as brasile, logwood, turnsole, rinds of wallnuts, wood soot, &c. these when boil'd are to be kept close stopp'd in glasses, till you have occasion to use them.