GLA
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GLA
Stones of the Place, accidentally mix'd with it, a Vitrifica- tion was undefignedly made. From whence the Hint was taken, andeafily improved.
Indeed, how old foever Gtafs may be 5 the Art of making, and working it, appears of no great Antiquity— The firffc Place mention'd for the making hereof, is Sidon in Syria, which was famous for Glafs and Glafs-houfes, as obferv'd by Wliny, X. XXXVI. c. z6.— The firft Time we hear of Glafs made among the Romans, was in the Time of TtberinSj when Wliny relates that an Artiff was put to death for mak- ing Glafs Malleable. See Malleability.—
Venice, for many Years, excel I'd ail Europe for the Fine- nefs of its Glaffes. The great Glafs-zvorks were at Muran, or Mouran, a Village near the City; which furnim'd all Europe with the fineft and largeft Glaffes. But within this fifty Years the French and Englijb, have not only come up to, but even furpafs'd the Venetians h fo that we are now no longer fupplied from abroad.
'the French made a confiderable Improvement in the Art of Glafs, by the Invention of a Method to caft very large Plates ; till then unknown ; and fcarce pra&ic'd yet, by any but themfelves, and the Englijh.
That Court applied itfelf with a laudable Induftry to cul- tivate and improve the Glafs Manufacture.— A Company ofGlafs-men was eftablifh'd by Letters Patents; and it was provided by an Arret, not only that the working in Glafs Should not derogate any thing from Nobility, but even, that none but Nobles mould be allowed to work therein.
Ingredients' of Glass, 'with the Method of preparing them.
The Materials ufed in the Compofition of Glafs, we have obferv'd, are Salt; and Sand, or Stone. See Salt, and Sand.
The Salt is of the hVd Kind ; fuch as will not evaporate with the moil intenfe Heat.— The Sand, or Stone rauft be fuch as will melt eafily: This is what gives Firmnefs and Confidence to the Glafs.
i° This Salt is procured chiefly from a kind of Afhes, call'd Wolverine, or Rochetta, brought from the Levant, and par- ticularly from Alexandria and Tripoli—The Afhes are thofe of a Vegetable, frequent in the Country, commonly call'd Kali; {ometimes Kalli 5 Kallu; Call; by Gefner, Alkali; by Lohel, Soda ; by jDodon<£US, Salfola ; and by Carrier. CordtiS, Fuchfius, &c. Anthyllis. Dr. Merret calls it En- glim Salt-wttrt, from its Saline Tafte ; and Glafs-wced, from the Ufe made of its Afhes in making of Glafs. See Kali and Polverine.
Saubin mentions ten Species of this Plant ; whereof there are four ufed by the Alexandrians, &c. for the making of Wolverine, and Soap; viz. Kali geniculatum ; Kali fe- ennda fpecies ; Kali JEgyptiacum ; and Kali Spinofum.
The firft and laft, our own Coafts affords, where they are call'd by the People Frog-grafs, and Sea-grafs ; but they are of no ufe for making of Glafs : Being laid on a hot Iron, they fly off almoft wholly in Fumes, leaving no A flies at all ; whereas the Kalies brought from the Levant, applied on the fame Iron, are foon converted almoft wholly into Wol- verine, i.e. very faline Afhes, of a dark Colour. See Soap. To get the Salt from this Wolverine, they pulverize, and lift it very fine ; then boil it in a Brafs Copper, with fair "Water and Tartar, till a third Part of the Water is con- fumed ; taking care to ftir it from time to time. Then, fil- ling up the Copper with frefh Water, they boil it a fecond time, till half be confumed : This done, they have a Lee impregnated with Salt, To get the Salt from the Lees, they boil them, till the Salt moots at the Top ; which they fcum off as it rifes. An hundred Pounds of Afhes, this way, ufually yields eighty or ninety of Salt.
When the Salt is dry, they beat it grofly, and put it into a. Furnace, to dry it further with a gentle Heat. When fuificiently dry, they pound and fift it very fine, and lay it by to make Frit. See Frit.
Note. Inftead of the Afhes of the Plant Kali, thofe of Fern will alio yield a Salt, which makes excellent Glafs ; nothing inferior to that of Polverine. The Method of Pre- paration is the fame. Add, that the Afhes of the Cods, and Stalks of Beans ; as alfo thofe of Coleworts, Bramble Bufh, Millet Stalks, Rufhes, Fern Rufhes, and many other Plants may be us'd for the like Purpofe, and after the fame manner. 2 For Stone, the fecond Ingredient in Glafs. — The beft, we have obferv'd, is that which will melt, is white, and trans- parent. This is found principally in Italy, being a fort of Marble, call'd I'arfo : The next is ^uocolt, or Cucgele, a fort of Pebbles found at the Bottoms of Rivers.
Indeed, nothing makes finer and clearer Glafs than Flint, but the Charge of preparing it, deters the Glafs-men from ufing it. The Preparation neceffary for Stone, is to cal- cine, powder, and fierce it.
Ant. Neri obferves, that all white, tranfparent Stones, which will not burn to Lime, are fit to make Glafs $ and
that all Stones which will ftrike Fire with Steel, are capable of being employed in making of Glafs. But this latter Rule, Dr. Merret obferves, does not hold univerfally.
Where proper Stone cannot be had, Sand is us'd : The bell; for the purpofe is that which is white and fmall; for green Glafs, that which is harder, and more gritty : It is to be well wafh'd ; which is all th^ Preparation it needs — Our Glafs. houfes are furnifh'd with white Sand for their Cryftal Glaffes from Maidfione 5 and with the coarfer, for green Glafs, from Maidftone.
Some mention a third Ingredient in Glafs, viz. Manga- ncfe, or Sydera, a kind of WJettdo Loadltone, dug up in Germany, Italy, and even mMendip Hills in Somerjetfbire. But the Proportion hereof to the reft, is very inconfiderable ; befide, that it is not ufed in all Glafs. Its Office is to purge off the natural greenifh Colour, and give it fome other Tin- cture requir'd.
Method of making White, and Cryftal Glass.
There are three forts of Furnaces us'd in the Glafs-works ; One to prepare the Frit, call'd the Calcar : A fecond to work the Glafs $ and a third, call'd the Leer, to anneal it. See them all defcribed under the Article Furnace.
To make Cryftal Glafs, take of the whireft 'Zrtr/0 pounded fmall, and fierced as fine as Flower, two hundred Pounds ; and Saltof Wolverine, an hundred and thirty Pounds. Mix them together, and put them into the Furnace call'd Cal- car, firft heating' it. For an Hour keep a moderate Fire, and keep ftirring the Materials, that they may incorporate and calcine together. Then increafe the Fire for five Hours : Af- ter which take out the Matter; which being now fufficient- ly calcined, is called Frit. — From the Calcar put the Frit in a dry Place, and cover it up from the Duft, for three er four Months. See Frit.
Now, to make the Glafs, or Cryftal : Take of this Cryftal Frit, call'd alio "Bollito; fet it in Pots in the Furnace, adding to it a due Quantity of Manganefe - When the two are ifufed, caft the Fluor into fair Water, to clear it of the Salt, call'd Sandevery which would otherwife make the Cryftal obfeure, and cloudy. This Lotion muft be repeated again, and again, as oft as needful, till the Cryftal be fully purged. Then fet it to boil four, five, or fix Days ; which done, fee whether it have Manganefe enough 5 and if it be yet green- ifh, add more Manganefe, at Difcretion, by little and little at a time ; taking care not to overdofe it, by reafon the Manganefe inclines it to a blackifh Hue. Then let the Metal clarify, till it become of a clear, and mining Colour: Which done, it is fit to be blown, or ibrm'd into VeffeJs at plea- fur e.
There are three principal Kinds of Glaffes, diftinguifh'd by the Form, or manner of working them ; viz. Round Glafs, as thefe of our Veflels, Phials, Drinking Glaffes, Ike* I'able ox Window Glafs, of which there are divers Kinds, viz,. Crown Glafs, Jealous Glafs, &c. and W late Glafs, or. Looking Glafs.
Method of Working or Slowing Round Glass.
The Working Furnace, we have obferv'd, is round, and has fix Soccas, or Apertures: At one of thefe, call'd the great Socca, the Furnace is heated, and the Pots of Frit fet in the Furnace : Two other, fmaller Holes, call'd Socca- cellas, ferve to lade or take out the melted Metal, at the End of an Iron, to work the Glafs. At the other Holes, they put in Pots of other fufible Ingredients, to he prepared, and at lafl: emptied into the Lading Pot.
There are fix Pots in each Furnace, all made of Tobacco- Pipe Clay, proper to fuftain not only the Heat of the Fire, but alfo the Effect of the Polverine, which penetrates every thing elfe. There are only two of thefe Pots that work : The reft ferve to prepare the Matter for them. The Fire of the Furnace is made and kept up with dry, hard Wood, caft in, without Intermiflion, at the fix Apertures. This they never omit, not even on the moft fblemn Feftivals.
When the Matter contain'd in the two Pots is fuificiently vitrified, they proceed to blow, or fafhion it : The Procels whereof we fhall here deliver from Agricola, Dr. Merret^ the French tDiffion. de Commerce, &c,
The Operator, or Servitor (the Meral being now fuf- ficiently refined) takes his Blowing Iron, which is a hollow Tube, about two Foot and a half long; and dipping it in the Melting-pot, there turns it about : The Metal iiicks to the Iron, like fome glutinous, or ciammy Juice, much like but more firmly, than Turpentine, or Venice Treacle-
For each Glafs he dips lour times, and at each Dip ro'ls the End of his Inftrument, with the Glafs thereon, on a piece of Iron, over which is a Veflel of Water; the Cool- nefs whereof helps to confolidate the Glaf more readily, and difpofes it the better to bind with the n^xt to be taken out of the Pot.
After
