Dictionarium polygraphicum. (Glass of Lead.)

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
The way of making Glass of Lead, commonly called Vitrum Saturni: to calcine Lead, and extract from it the colours of emerald, topaz, sea-green, or azure granate, sapphire, gold, and other colours.

Glass of Lead known to few artists in this way, because they make no use of it by reason of its brittleness, is beyond doubt the fairest anf noblest glass of any other.

In this glass you may imitate all the colours of oriental precious stones; and if this glass was as tough as crystal, it would far surpass it in beauty.

It is true, if you don't work it with great care, no pots or crucibles will hold it, for it will crack them and run out. I will here give all the methods of preparing it; and that so distinctly, that the unexperienced may succeed in it.

The business principally consists in knowing well how to calcine the lead, and re-calcine it again, which is commonly known, notwithstanding it shall be shewn how to do it, for the sake or those that do not know it.

The better the lead is calcined, the less apt it is to turn into lead again, end break the pots in its operation.

We will also shew, that you must alway drop the glass into water, when it is melted, for the least lead remaining in it, breaks out the bottom of the vessels, and so use your matter, which may be avoided, by carefully minding what we have, and which we shall note again in the following articles.

It is highly probable, that that subtilty, whereby the lead so easily in this case pierces the pots, when it is not wholly calcined, comes from a certain unctuous yellow nutter like oil, that is seen to swim on the top sometimes in a violent fusion.

For it has often been observed, that if that unctuous matter be not taken off, as soon as it appears on the top, it will pierce the pot, and so all run out among the coals.



The way to make glass of LEAD.
The beauty of this glass is, that it may be ringed of several colours, as black, white, gieen, and red, which are natural to it, the degrees of the fire only making it take those different colours.

This glass being well made, communicates its beauty to glass, and to tinctures of precious stones, wherein it is employed.

To make vitrum saturni, take 15 pound of calcined lead, and 12 pound of crystal or rochetta frit, according to what colour you would have; mix them well together, put them in a pot in the furnace, where 10 hours afterwards it will be in good fu fion; then cast the whole into water, and take out speedily the remaining lead at bottom of the vessel, for fear it should break; then take it out of the water, and dry and put it into the same pot to melt again: Take care pot to put in the grains of lead (if there be any) which were in the water, and which will be loosened from the matter.

After your matter has been again in fusion 6 hours, you may work it.

You may also make a glass of lead, by taking 3 parts of lead, and one of fine sand, and change them into glass in the furnace, as also of 3 parts of calcined litharge, and one part of calcines flint, melted and vitrified in the furnace together.


The way how to work Glass of Lead.
It is not enough to shew how to make glass of had, if we don't shew how to work it too.

If any one would make a vessel for use, of any figure, he must take a glass-worker's iron they use to take metal out of the pots with, and take what quantity of glass of lead with it he pleases, when it is in fusion: let it a little cool, then work it after the manner used by glass-workers.

You must clean well the marble you make use of, and while the glass is cooling, you must wet the marble with cold water, for otherwise the glass would scale it, and part of the marble would stick to it.

If the marble be hard, you have fb much the less to sear, for it will not break so easily, nor stick to the glass.


To make glass of Lead a fair emerald colour.

The easiness of tinging glass of lead of any colours is the reason you may be sure of giving it an excellent emerald-green, especially because green is natural to it.

Take 20 pound of crystal frit, powdered and searced, and 16 pound of calx of lead also sifted, mix them well together, then put them little by little into a pot heated in the furnace, and 8 or 10 hours afterwards it will be melted, then cast the melted matter into water, and carefully take the remaining lead from it, then putting the matter after it is dried in the same pot again, 7 or 8 hours after it will be again melted.

Reiterate this process, casting the melted matter into water, and separating the lead that sticks to the pot, as before; then this glass will be cleansed and purified from all the foulness and unctuosity the calx and powder would leave in it, and be very re-splendent.

You must put it again in the pot, where it will melt and putrify in little time.

When it is melted, put to it 6 ounces of scales of copper thrice calcined to powder, with 24 grains of crocus martis, made with vinegar also in powder, and mix them together.

This powder must be cast in at 6 times, always mixing well the glass, and taking at each time the interval of saying the creed. Let it rest one hour, and then stir it again, and see if the colour pleases you; if it be as you would have it, let it stand 8 hours, that the whole may well incorporate.

Then stir it well, and let it rest a little, that the fæces may precipitate to the bottom of the pot, tho' it may be wroughr, and the colour can scarce be distinguished from a true emerald.



Another way of making Glass of Lead of a fairer emerald than the former.
For this colour which will be fairer than the precedent, you must change your ingredients, and instead of scales of copper thrice calcined, put the same dose of caput mortuum, of vitriolum veneris prepared, then proceed exactly as in the former article, and you will have a very exquisite green.


To make a Glass of Lead the colour of Topaz.
Topaz is a lighter colour than emerald, and casts rays the colour of gold; wherefore the colour cannot be well imitated except this way.
Take 15 pound of crystal frit in powder, and 10 pound of calx of lead also in powder, mix them well, and searce them very fine; then put them in a pot heated at the furnace, where leave it 8 hours, that it may be melted.
Then cast the matter into water, and take out of the pot all the lead (if there be any) that remains.
Put the matter again in the pot to be melted, and cast it by intervals into the water; and to tiiat matter half its weight of glass tinged of a golden colour, incorporate well, and purify the whole together, and you'll have a glass of the colour of oriental Topaz fit to be wrought.


To make a sky or sea-green in glass of Lead;
As is shewn in several places elsewhere, to tinge glass of a sky-colour or sea-green, this would be needless to repeat here.

That we now shew, which is made in glass of lead, has no less beauty.

Take 16 pound of crystal frit, 10 pound calx of lead, mix them together, and put them gently into a pot heated in the furnace, where they will be in good fusion in 12 hours time, then cast the matter into water, as has been shewn before, take the remaining lead out of the pot, and put your matter to melt again 8 hours, after call it into water again, taking the remaining lead out of the pot, then it will be well purified.

Put it again in, to melt in the same pot, and when it is in good fusion, cast in at different times 4 ounces of small copper-leaves prepared (see article Copper, &c.) and a quarter of an ounce of zaffer prepared, (see the article Zaffer, &c.)

After having mixt these powders well together, and the matter at each casting of it in; 2 hours after stir the matter well in the pot with an iron rod, and make an aflay to see if the colour be full enough; then let it stand 10 hours to purify, and to give the colour time to incorporate with the glass, then it may be wrought to the uses you design it, stirring it well, and letting it rest a little to settle before you work it.


To make a sapphire colour in Glass of Lead.

The beauty of sapphire is no less imitable in of than the colours of other precious stones; and its clear blue transparent colour will have as much splendour.

To make it, mix together 15 pound of crystal frit in powder, and 12 pound of calx of lead, then, searce it, pounding again what does not pass through the sieve; add to that 2 grains ot prepared zaffer, 24 grains of manganese of Piedmont also well prepared, mix the whole well together, put it in a pot heated in a furnace- and let it stand to melt during the space of 12 hours; then cast the vitrified matter into water, and carefully take away the lead that remains in the pot; then put the matter again into the same pot, and let it stand to be re-purified 12 hours.

Then see if the colour pleases you, and you may work it; you'll have a colour like the true oriental sapphire.



The way to make a golden colour in Glass of Lead.

This colour is as fine in glass of lead as crystal, it takes that colour both from the lead and the ingredients mixt with it.

Take 16 ounces of good crystal, frit in powder, to which add the same weight of calx of lead also in powder, and well searced; then add 6 ounces of copper scales thrice calcined, and 48 grains of crocus mar tit made with vinegar, the whole mixed well together, put it into a pot heated in the furnace, 12 hours after cast the glass in water, and take the remaining lead out of the pot, and then put the matter again into the same pot to be well purified during 12 other hours.

After that stir it well, and sec if the colour pleases you; if it chance to be greeniih, add to it some crocus martis, and the greenness will vanish, then you'll have a golden colour very fine, which may be wrought.

These be all the colours that are given to glass of lead alone; we shal' augment the number in a paste of lead, (whereof you will find the preparation in the articles Paste in letter P) because it is useful for imitating precious stones.