Dictionarium polygraphicum. Blue enamels.

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
I. BLUE ENAMELS or turcoise.
Take of the mixture for Enamels six pounds, zaffer prepar'd three ounces, copper twice calcin'd one ounce twelve grains, reduce all to a fine powder; put it into a white glaz'd earthen pot, when the metal is well melted, cast it into water, dry it, and put it into the pot again, and let it stand till it is well melted, purified and incorporated; then take it off and make it up into cakes.

II. Another noble blue.
Take of the mixture six pounds, plates of copper calcin'd three ounces, zaffer prepar'd one ounce twelve grains, these being reduc’d to a fine powder, mix and melt them as before, casting it into water; dry it, and return it into the pot again to melt, purify and incorporate, then take it off and make it into cakes.

III. These glorious blues are admir’d by most people, as being the most agreeable to the fight of all others; their beauty and splendour being so great and transcendent above all other colours, they only having the resemblance of heaven itself; for which reason the Romanists esteem it a sacred colour.

IV. A blue turcoise Enamel.
Take of the mixture six pounds, put it into a white glaz'd earthen pot, melt and purify it, cast it into the water, and dry it, put it into the pot again, melt it and add to it at times the following mixture.
Take scales of copper thrice calcin'd three ounces, zaffer prepar'd four scruples and fix grains, manganese prepar'd eighteen grains, all reduc’d to a fine powder; mix them and stir the mass very well each time with your iron hook, that the powders may incorporate; being well coloured, take it out and make it into cakes.
But you must observe, that the colour is right good and perfect, before you empty your pot; for experience must teach you how to proportion the tinging ingredients, as to more or less; if there be too much of the tinging matter add more of the mixture, if too faint, add more of the tincture or tinging matter or powder, till the colour is as you would have it.
As this colour is very fine, so it is very difficult to make well, and requires many trials and much experience; therefore you must not be discourag'd, if you sail in your first essays; for by continuing to make farther trials, you will at length effect what you desire; and be able to judge and know, when you are in the right, and when in the wrong.

A blue for painting on Enamel.
Take any of the foregoing Enamels, purify them with aqua fortis, and grind them with oil of spike as for other colours; these are some of the noblest that can be us’d for this work.
2. Take painter's Enamel prepar’d, put it into a glass bottle, add to it aqua vitæ, so as to cover it four inches, four times a day, so will the grosser parts fall to the bottom; decant the clear liquor, evaporate the spirit, and dry your azure, and it will be very fine; then grind it on a marble, and it will be fit for this work, and far beyond ultramarine; which yet may be made use of as occasion requires.