Dictionarium polygraphicum. Frit, fritt.

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.
FRIT, FRITT is the matter or ingredient, whereof glass is to be made, calcin'd or bak’d in a furnace. See GLAss.

Frit is a salt drawn from the ashes of the plant kali, or from fern, which mix'd with sand or flints and bak'd together, make an opake mass.

Pliny describes flint to be a fine sand from the Volturnian sea, mix’d with three times the quantity of nitre, which being melted makes a mass call'd ammonitrum, which reboil'd makes pure lass.

Neri observes, that Frit is only the calx of the materials that make glass; which though they might be melted, and glass made without thus calcining them, yet it would take up much more time.

This calcining or making of Frit, serves for mixing and incorporating the metals together, and evaporating all the superfluous humidity.

There are three kinds of Frits; the first is crystal Frit or that for crystal metal, made with salt of polverine and sand.

The second and ordinary Frit is made of the bare ashes of polverine or barillia, without extracting the salt from them. This makes the ordinary white or crystal metal.

The third is Frit for green glasses, made of common ashes without any preparation. This last Frit will require ten or twelve hours baking.

The materials us'd in each are to be reduc’d into a fine powder, wash'd and searced; then equally mix’d, and frequently stirr'd together in the melting pot. See GLAss.

The way to make Frit for crystal.

The name Frit is generally known in all glass-houses, for the first preparation of matter to make glass and crystal, which is made in the first oven call'd calcar.

To seek the etymology of it, will not be necessary to our present purpose, it is apply'd to the drying the matters in this furnace, where they are reduc’d into great and little lumps.

We think it sufficient to say, that to make fine and perfect crystal, there must be had matter fusile and capable of being rendred white and transparent in the fire.

We have already told you, that salt is the first and principal matter for this work, here we will add, that the next, and which gives glass its consistence, body or hardness, is sand or some sorts of stones, just as copper gives consistence to Roman, Dantzick and Hungarian vitriol and others; which would otherwise run into [...] moist places.

Whence it comes to pass, that the clearest and most transpa rent glass, made of the finest and most pure salt, will dissolve in earth or in moist or cool places, if there be more salt in proportion than sand or tars, by a separation natural to those two matters; it is for this reason, that some assert, that putting poison extracted out of minerals into Venice glass, the great cold of it will dissolve the glass.

All this depends upon the composition of the Frit, wherein the quantities of salt and tars ought to be rightly proportioned to one another, to make the glass more or less fixed.

Several authors have given the name tars to all matters, which give consistence to glass when they are calcin'd.

Agricola in his twelfth book says, that white stones when melted, are the best ingredients in this art; for this reason, they ought rather to be employed than any others for making crystal. Pliny says, that authors affirm, that the stones in India glass is made so excellently transparent, that no other is comparable to it.

The Venetians, who make glass in the Isle of Muran as well as those in Italy, make use of a white flint, which they have out of the river Ticinus; where there is abundance of them, as also o the river Arnus, both above and below Florence, and in other places.

They use also a rich sand full of salt, which they find in Tuscany and in the Vale of Arnus, as also a sort of hard white marble, which is found in Tuscany known to every body; it grows at the foot of the little mountains Pisa or Sarvavezza, Massa or Carrara, that ought to be chosen, which is very white; which has no black veins, nor yellow or red stains in 1t.

Of all of these materials may be made very white tars, and also very fine glass and crystal.

Ferrandus Imperatus, l. 24. c. 16. makes mention of Luocoli, and thus speaks of it. The glas-stone is like in appearance to white marble, being somewhat transparent, but had as a flint, whence being struck, it will sparkle and put into the fire turns not to lime; that it is of a light green like the serpentine stone, having veins like Venice talk, that being cast into a fire, it ceases to be transparent, and becomes light and more white, and more light, and at length is converted into glass.

It is certain, that all white and transparent stones, such as will not become lime, are very fit for making glass; that all fire stones, and those which strike fire when they are calcin’d and reduc’d to an impalpable powder, and sifted through a very fine sieve, make an incomparable pure and fine crystal; and all the art consists in reducing the tars to such fine impalpable powder, but the great trouble in doing it, has made the glass men give it over.

They make use now a-days, much more of sand than offlints, because there is little or no expence in its preparation, which only consists in washing it clean, and afterwards drying it and sifting it before you use it, and that is all; this is the first matter or ingredient for making glass; but flints being found better and more fine, they afterwards made use of them, nothing but the parsimony and covetousness of the times had brought the other in use again; because glasses made of that may be afforded cheaper.

Crystal requires a soft and white sand, common glass one more rough, hard and grating like a file; sands differ very much from one another, for some will melt quickly, and mixing with the salt immediately be converted into glass; others again will endure a strong fire, but in general there is no sand, but what may be made into glass.

To make Frit, you must have two hundred pounds of tarso, prepared as we have shewn, or fine sand, and mix therewith about one hundred and thirty pounds of salt, also prepared after the manner elsewhere mentioned. See TARSO.

Care must be taken to mix the two materials well together, then to put them into the furnace to be calcin'd, after it has been well heated to make the Frit.

During the first hour, the fire must be moderate, and the Frit continually stirred with an iron-rake, that the materials may the better incorporate; then the fire must be increased to a very strong heat for the space of five hours, continuing always stirring the Frit with the rake, which is very necessary to the preparation of it.

After the space of five hours the Frit (having had sufficient fire) will be made and reduc’d to lumps about the bigness of a filbert, which (if it be enough) in breaking will be light and white without any yellow; for if you find any of that, you must put it into the furnace again, till it lose that yellow colour which it will infallibly do.

By how much the more the materials are stirred and calcin'd in the furnace, they will be so much the more refin'd, and melt more easily in the pots; after this you take it out of the furnace, and let it cool; then you lay it on boards in a dry place, otherwise the moisture would cause the salt to melt into water, and only the tarso would remain behind, which of itself would never be made into glass.

After this you cover it well for fear of dust, for you must take a great deal of care and caution to have a fine crystal.

The Frit thus made, ought to be as white as snow, but during the time it is making, you must try whether the quantities are well proportioned or not, which must be done by putting some of the Frit into a crucible, and afterwards on a clean piece of glass; where it may be seen whether it be well made by its joining together, and being clear, if it be too hard or too soft, you must increase or diminish the quantity of salt in it; which those experienced in the art, know very well how to do at first fight; this being well prepared and kept in a dry place, will last three or four months; nay, it will grow better and more fit to unite together speedily.

The way of making ordinary FRIT of polverine rochetta or barillia of Spain.

FRIT is nothing but a calcination of the materials mixt together which make glas.

Although those materials would melt and be converted into gloss, without this calcination, yet use and reason have dictated this way, since otherwise it would take up a great deal both of time and labour.

To avoid which this way of calcining the materials in furnaces was found out, which being rightly made, and the doses in the composition of it justly observ'd, it may immediately be put into the pot to be clarified before it is wrought.

Frit made of polverine makes ordinary white-glass, and that which is made of rochetta of the Levant, makes a very fair crystal; and that which is made of barillia of spain, makes a glass not so white and fair, being commonly somewhat unctuous, which makes the glass incline to an azure or blueish colour.

To one hundred pounds of barillia, you may put eighty five or ninety pounds of fine tars (see TARSO) and you must regulate that dose according to the goodness and fatness of the Barillia, which experience will teach you.

Then you must mix fix or eight pounds of good sand with the dose, after having well wash'd, dry'd and sifted it, and of the whole you make a Frit, which will produce a very white and fair glass.

This Frit being calcin'd in the furnace, you must take it out hot, and throw upon it three or four pails of cold water; and then put it in a moist and coid place, after which you must from time to time sprinkle it with a small lee for the space of three months, which will render it as hard as stone. So that you cannot break it without a hammer; this frit will melt easily, and makes a very white glass almost like crystal, but easier to work.

The lees, which communicate to it their salt, work this effect, and augment the Frit; if the lees should fall short, or you have none, you may water it with common water, which although it is not so strong as the lee, yet it is useful.

To make this small lee, you must use the earthy parts or faeces, which settle in your earthen pots; when you make strong lees, as follows.

You must fill the same vessels with common water a little heated, and let it stand therein, long enough to extract the salt that remains; afterwards you take out that water gently with an iron-ladle, without troubling the faces, and filter it, to clarify it, and afterwards let it stand some time to settle, and then keep it for the use abovesaid.

These lees will be still pretty sharp and full of salt, communicate it to the Frit in watering it, and by this means none will be lost.

It is true in our modern times, wherein workmen rather seek to abbreviate than embellish their work, there are but very few that take the pains to water their Frit after this manner. Yet as that Frit is the finest, most fruitful and most easy to melt, we thought it worth while to propose it.

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