Dictionarium polygraphicum. The way to make Turcoise.

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.
The way to make Turcoise.

The name of Turcoise, which this precious stone bears, comes from the place where it is found, viz. in Turkey; altho' this stone comes also from Persia and the East-Indies, where it is found in abundance, the colour whereof approaches nearer to blue than green, which also distinguishes them from those that come out of the west, which are more green and whitish.

They call the first by the name of the stone of the old rock, and the other by that of the new.

The Turcoise is the finest and noblest of all the opake precious stones: its colour is composed of green, white, and blue, and imitates that of verdigrease.

Take ten ounces of natural crystal prepared, and Saturnus glorificatus; half an ounce of purified verdigrease, and one ounce of our prepared zaffir, the whole in hue powder; which mix well together in a crucible covered, with another well-luted and dried, which afterwards put into a glass-house furnace, where leave it for three hours; then twelve hours in the annealing furnace, that it may cool gently; then take out your crucible, and break it, and take out the matter, and cut and polish it, and you'll have Turcoise-coloured stones like those of the old rock.

The way of making Turcoise-blue, a particular colour in this art.

For this colour take a pot-full of crystal-frit ringed with an aqua-marine colour, or blue, whereof we have given several preparations, which colour must be fair and full, for all depends on that: it being well-melted, put into it, little by little, sea-salt decrepitated white, and reduced to powder, mixing it well and softly, as we have noted in speaking of other metalline colours; and the blue, from clear and transparent, will become thick: for the salt penetrating the glass, takes away its transparency, and causes a paleness; hence alone comes the Turcoise-colour used in glass. When the colour is right, to the workman's fancy, it must be presently wrought, for the salt will evaporate, and make the glass transparent and disagreeable; if in working this metal the colour fades or goes off, you must add a little more of the same decrepitated salt, as before, and the colour will return.

We will here advertise the workman, that he mud take care, that this salt be well decrepitated, otherwise it will always crackle and be apt to fly in his eyes, and endanger his sight; you must (as I have said) put in the salt in intervals, 'till the colour pleases you.

It will suffice for this use, that the frit tinged aqua-marine, or blue, be made of one half crystal-metal, and the other of rochetta, and the colour will be very fair and good.

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