The art of glass shewing how to make all sorts of glass, crystal and enamel : likewise the making of pearls, precious stones, china and looking-glasses : to which is added, the method of painting on glass and enameling : also how to extract the colours from minerals, metals, herbs and flowers ... : illustrated with proper sculptures / written originally in French, by Mr. H. Blancourt, and now first translated into English ; with an appendix, containing exact instructions for making glass-eyes of all colours.

OF THE ART OF GLASS. (Book 12)

BOOK XII. To make Crystal Looking-glass: How to Grind, Polish, Diamond-Cut, and Silver them: To Make Glass and Metal Mirrours, &c. (Book 12)

CHAP. CCL.

THIS is the Twelfth and last Book of our Art of Glass, which should have indeed succeeded the First; but we waited some Memoirs on the Subject, nor we have not yet found them; this made us put it off, and place it here: Besides, there is such a Coherency of Matters, in the Order of the Second Book, as we could not pos∣sibly dispose of any other way, without breaking

their due Course, and the Affinity and Connection they have with each other, which the Reader may easily perceive; but what matter is it where we place this, so that it may be found among our Works; and we deliver nothing therein, but what we have been familiar withal.

That of Looking-glasses is undoubtedly the finest and more admirable part of Glass-Work; 'tis the most perfect Master-piece of all the Art. We pre∣sume the Order we have given in placing it here, will be approved of, since 'tis the Subject of the last Book, and the Twelfth, which is a perfect Number, and comprehends all other in Sacred Philosophy.

Twelve, the Number of Grace and Perfection, has been highly esteemed at all times for those Won∣derful Properties ascribed to it; 'tis very much ce∣lebrated in Holy Writ, and the Divine Plato has u∣sed it with the same Deference in his Works, if the Account which those, who were intimate with this Famous Number Twelve, have left of it, were not Foreign to our Design, we could give the Curious such extraordinary Relations, as would create a Mighty Respect in them for the same.

We already noted in the First Chapter, that 'tis about Two Hundred Years since the Invention of Looking-glasses, and also how they were found out: Before these the Ladies made use of Steel, or Cop∣per, or well polished Marble Mirrours, these have been in use for many Ages: We can by the help of History, look back on them as far as the Time of Ozias King of Iuda, which was about the Fourth or Fifth Olympiad; and as many Years before the Building of Rome; Seven Hundred and sixty four Years after this, our Christian Aera commenced. Now tho' the Tyrians were very conversant in Glass∣work, yet they had not the Knowledge of making Looking-glass.

Among all the Excellencies of the Art, none comes near this, nothing can be finer, or admit of greater Admiration, than to see that all the Actions of the Beholder, are so justly and lively represented in these Glasses, that he has an opportunity of disco∣vering what is to be valued on him, and correcting what's amiss; these Truths are too apparent for any to disprove; for the Experience of them are at this Day to be made as easily by the Meanest as the Greatest Persons.

We shall discourse but very briefly of the Metal for making these Glasses; for 'tis the same Crystal we have prescribed throughout the First Book, but we will enlarge on this Matter a little, for the con∣veniency of making the Mirrours of Metal, &c. whereof we'll shew how to compound the Stuff, and the way of working them.

CHAP. CCLI. The Way to make Looking-glass.

ALL those who employ themselves in the Art o•• Glass, do it always without derogating from their Quality, as we have noted in Chap. 3. which our Kings have always taken care to maintain.

The Undertakers of the Royal Glass-Manufacture in France, when they obtained their Grants of Pri∣viledges, did at the same time require, That al•• Persons of Quality, who should associate in the Ma∣nufacture, might do it without lessening their Quali∣ty; to which his Majesty agreed with Exemptio•• from their Taille, and several other Privileges, a•• Quartering of Soldiers, &c. for all such, their Sub∣stitutes, Servants, and Domesticks.

The first Grant of Priviledges to this Manufa∣cture, bears Date in October 1665. in Favour of Nicholas du Noyer, for Twenty Years, which was renewed by Letters Patent of the last of December 1683. for Thirty Years to Peter Bagneux.

The second Privilege for the Manufacture Royal of Large Glass, was granted Decemb. 14.1688. to Abraham T' Hevart, for Thirty Years, with the saving Pri∣vilege of Nobility as the former: These having set∣led at St. Gobin, near La Fere, did by Letters Patent of February 1693. obtain Exemption from the Tailles, (or Subsidy on the Third Estate, which is a constant Tax) and other Impositions, as well for themselves, as their Deputies and Servants.

And to avoid all Contest, these two Manufactures were united by Order of the Council of State, April 19. 1695. and Confirmed May 1. following, under the Name of Francis Plaistrier.

Now for making these Glasses, the same Crystal assigned throughout Book 1. is sufficient; the Dif∣ference is only instead of Working it as you do there, to cast it flat and not blow, as in Chap. 3. to which we refer the Reader.

The Manner of Casting the Metal, did not com∣mence with the Invention of Looking-glass; for the Workmen at first, used to take a piece of Metal ve∣ry large, clipt and done on the Marble into Quarries as big as they'd have them; these they set after∣wards on a Pallet of Iron in the Furnace, till they were in a Fusion, and so spread and united; hence they took and put them into another little Furnace for that purpose, S. S. S. with fine searced Ashes to Bake; this done, they raised the Fire by degrees, and so let it go out again, and drew off the Glasses, working them after our manner in the next Chap∣ter.

Thus too they wrought their little Round Glasses, or Mirrours, first shaping them out of a long piece of Metal, by Circumvolution, and afterwards clip∣ping them as the former, so finished them in the Furnaces, and made them fit for Polishing.

Since that time having attempted to make them very large, they fell upon the Way of Casting the Glass like other Metal on Sand Beds, such as the Founders use; and to perform it the better, they have a Roller of Metal to run over the Surface of the Glass Metal for enlarging the Plate, and to smooth and compact it withal.

For such as would make them very large indeed, as are wrought at Muran near Venice, and in our Royal Manufacturers, they had a much better, and easier Method than doing them on Sand, viz. in large Tables of well polished Copper, whereon they cast the Metal, but these not having strength enough to abide the Heat, we have since made use of Iron, which will sufficiently perform the Effect.

These Tables whereon the Glasses are at first sight Cast to their proper Largeness, must have their bottom sunk as low as you intend the Thickness of your Glass-Plate, and have a Conveniency to push it out, as soon as ever 'tis prepared thereon.

Some make use of Marble ones with Covers, o∣ver which they have a Plate, or Runner of Metal, to slide and press it on the Glass Metal, that the Glass Plate may be the more compact and even.

Thus are large Glasses made, which are no less surprizing than pretty, and 'tis a very considerable Improvement they are brought to at this Day, of making them so extraordinary large for Mirrours: One would admire to what Perfection the Wit of Man may arrive at, and is capable of bearing from the advantage of Serious Application and Study in profound Matters.

CHAP. CCLII. To Grind, Polish, and Cut the Looking-Glass.

AFTER you have it from the Furnace, you must lay it on Sand, in a convenient place to strengthen, else it will break in Working it; then grind it on very fine Sand and Water.

This time 'tis that the Workmen give it the first Fashioning; then they do it over again with Powder of Emery instead of the Sand, and so give ••t a second Improvement; when they have done it enough with these two, they do it a third time with Tripoly instead of Emery, this Polishes the Glass per∣fectly; others give these Glasses a fourth Process with Calx of Tin, to bring them to a very extraor∣dinary Lustre and Polish.

The Diamond-Cut is done by Grinding the Cry∣••tal on Drift Sand and Water, as much as you think ••onvenient.

These are the several Methods for finishing the ••ooking-glass all to the Silvering, which must be disposed thereon, as in the next Chapter before it ••as the Quality of a Mirrour.

CHAP. CCLIII. To File, or Silver the Looking-Glass.

THE Glass is not perfected, till it be Silvered; for without that, it is impossible it should di∣stinctly shew the opposite Objects; 'tis the Filing or Silvering therefore which gives it its just Perfe∣ction.

For this you must have a firm well smooth'd Ta∣ble, much greater than the Glass, whereon spread one or more Sheets of very fine Tin, let them be as thin as Paper, and so prepared, as not to have any Rumple, Furrow, or Spot, else the Glass will be spoil'd: Over these Sheets spread good Mercury quite covering them with it; when the Mercury has soaked in well, place the Glass thereon, and it will stick to them; then turn it, and spread Sheets o•• Paper on the Filing; press it gently, smoothing an•• stroaking it with your Hands, to take off the Super∣fluous Mercury; then dry it in the Sun, or by a sof•• Fire, and it will become perfect.

But because 'tis not so easie to file the Large Glas∣ses as the small, you must have recourse to a Table for the purpose, with a Diamond-Cut rising Border, to keep the Sides of the Glass firm, whereon yo•• must lay it, with the Backside, (which is to be filed) upwards; then lay on the Sheeted Tin very smooth and closely; over these the Mercury,to dissolve them•• then with the Sheets of Paper cover all, and 〈◊〉〈◊〉 smooth, and run it over with your Hands to take a∣way the Surplus of the Mercury, and so dry it 〈◊〉〈◊〉 before.

The rest of the Work depends on the Framing them, and giving the suitable Ornaments accord∣ingly.

CHAP. CCLIV. How to make Spherical Concaves, and Convex Glasses, commonly called Burning Mirrours.

BEFORE we discourse of the Metal Mirrours, we will shew how to do such of Glass: The Use of these Glasses is to unite the Sun-Beams, and so kindle a Flambeau, Wood, or any other Combusti∣ble Matter. By them Metals also may be dissolved in a little time as easily as in a Crucible on a Furnace, or at a Forge.

The Whole Mystery of making them, is to have the Moulds of a Round Shape, otherwise they have but a very weak Effect on the Sun Beams; the Moulds must be so exactly made, as neither side shall differ from the other.

To make the Concave Glass, you must have the Mould Convex, and the Convexity thereof must be made by a Sphere, according as you have it greater or less; and 'tis from this Sphere the Convexity of the Mirrour must be taken: As for instance, Take a Sphere of what bigness you please, divide it equal∣ly, and also one of the Hemispheres in three equal parts, by Planes parallel to the great Circle, the Convex, Segment shall then be the sixth part of the whole Sphere, and the Measure of your Mirrour: To do this you may have recourse to the Works of Archimedes, Iohn Baptista Porta, Kircher, and many other Authors.

If you would make the Mirrour a Convex Glass, you must have the Moulds Concave, and these you may do two ways, thus: Take the two Concave Sides of the Mould, and closing them together equally, as the Founders do their Frames, pour in through the Mouth of the Mould your Crystal Metal, letting it fill the Mould, and afterwards cool. Another way is, to take two Concave Mirrours, and joyning their Faces, solder them well all about, only leaving a small Orifice, through which you may fill it with some Aqua Vitae, and so stop the Hole, and frame them with Wood, or Metal: This sort of Mirrour, has a more ready Influence on the Sun Beams then any other; we'll say something of the Effect there∣of when we come to speak of the Metal Mirrours, but upon the whole Matter you must have these Glasses all very well polished.

These Burning Glasses may be made Parabolick, or Spheroidal, and such have still a better Effect than the Spherick: You must proceed in Mould∣ing them as with the former; you must observe a just proportion in doing them; for when they are too much raised, they are hindered by their Deepness from having a good Effect; and up∣on this depends the Whole Nicity of the Art.

CHAP. CCLV. How to make Metal Mirrours, Concave Sphericks, or Parabolicks, usually called, Steel Burning Mir∣rours.

THE Authors cited in the former Chapter are very useful to be consulted on this occasion to demonstrate the Method, Use, and Excellency of these Mirrours; for which reason we shall say but little on that Subject.

The Moulds for them are prepared as in the for∣mer Chapter, whether Concave, or Convex, and for such as are flat, they may be cast on Sand.

The Metal of these Mirrours is called Steel, be∣cause it is of a very hard and bright Composure and Temper, and the harder the Metal, the better the Mirrour, and the easier to polish; the Whiteness of it is very convenient for giving the Quality of Burn∣ing, and not only for that, but several other Uses; if it be too Red, or Black, it alters the true Distance and Colour of its opposite Objects; you must there∣fore make them of this following Composition.

Take three Pounds of Copper, one Pound of fine Tin, half an Ounce of White Arsenick, an Ounce of Tartar: First, melt the Copper, then put the Tin in immerged in the Copper, else it will fume away in the Melting, and leave the Copper behind; these two being well melted together, cast in the Arsenick, and Tartar: After this let all melt for two or three Hours, and so Mould it.

Some Persons dose with the former weight of Copper and Tin, half a Pound of White Arsenick; ••thers instead of Arsenick,put in a quarter of a Pound

of Antimony. Here is another way to compound this Stuff of the following Ingredients; and after that another Composition much more excellent than ei∣ther.

Take a Pound of well refined Copper, melt it, then add three Pounds of fine Tin; as soon as these are well melted, add six Ounces of Red Tartar cal∣cined, one Ounce of Salt-petre, two Drams of Allom, and two Ounces of Arsenick, let these melt for three or four Hours, that the Salts may evaporate, and the Stuff will be fit for moulding; this Stuff is more solid and hard than the former, and much better to make the flat Mirrours for Looking. You shall be shewn how to polish them in the next Chapter.

We having promised to assign a much more ex∣cellent Stuff for Concaves than the former ones, will give it here; because of the hardness and compactness thereof, it is more capable of polishing, and conse∣quently much better than the rest.

Take Plates of Copper one Pound, mince 'em that they may be put into a Crucible, imbibing them with Oyl of Tartar; then powder a quarter of •• Pound of White Arsenick, and put these S. S. S. as we have shewn the Method elsewhere, until you fill the Cruci∣ble; pour on them afterwards Linseed-Oyl to co∣ver the Arsenick and the Copper; head and lute you•• Crucible, and when the lute is dry set it on a Sand-Furnace, letting the Sand arise no higher than the Head; heat the Furnace very gently till it arrive a•• a just degree, and the Oyl begins to evaporate; 〈◊〉〈◊〉 this time the Oyl will prepare the Copper for re∣taining the Arsenick, which must enter the Copper as easily as Oyl does Leather; set it again on fresh Sand, and increase the heat of the Furnace, giving i•• the same degree as before, until the Oyl evaporate•• and boyl up; then take off the Crucible, let it cool and break it, you'll find your Copper of several Co∣lours,

and would be much better, if instead of Arse∣nick, you made use of Orpiment.

Take of this Copper one part, of Latten two parts, melt the Latten on a smart Fire, and so put in the Cop∣per; when they are well melted, cast the Metal Drop by Drop into a glazed Earthen Vessel full of Water, over which lay a Bush, or Broom for the Stuff to go through; thus you'll have a Metal not to be touched with a File, nor Brittle, as good as any Steel for all uses whatsoever.

Take of this hard Metal three parts, and best Tin of Cornwall, which has no Lead in't, one part; melt the Metal before you put in the Tin; after these are well incorporated, you may fill your Moulds, &c.

This is the best of all our Compositions for ma∣king of all sorts of these Metal Mirrours; 'tis white, hard, not Brittle, and very easily polished exceeding fine.

CHAP. CCLVI. To Polish the Steel Mirrours.

WHATSOEVER Exactness you use in Mould∣ing these, they do never receive their true Shape and Perfection, until they are Polished and Burnished; in doing which, least you should spoil, or endamage them, you must Work away the Out∣side at the Wheel, with the Sand-stone, which the Pewterers and Brasiers make use of, and then apply the Handle, and Polish them sufficiently by rubbing with Water.

This done, take it off this Wheel, and put it on the Second, where rub it with Emery prepared, that

it may be finely polished, so as the Scars may be scarce perceptible. Do this in an Oblique Line.

Then take it off this, and set it on such another; rub it with Blood-stone prepared, and afterwards use Calx of Tin, working it for a long time, until it have its due Burnish and Perfection, still doing it in the same Obliquity.

You must keep these Mirrours from the Moistness of the Air, and Steams; or if they should happen to be endamaged by any such, you may restore them by rubbing on them a piece of Deer, or Goats Skin, humouring the Oblique Line; you must not use any Woollen, or Linen Stuff, for they spoil these Mir∣rours.

These Mirrours may be also polished with Lead Artificially melted, with Emery and Water, for the First Process; and very fine Emery and Lead for the Second; and in the Last, with Blood-stone and Tin Dross; these make a finer Burnish than the for∣mer; for the Mirrour is highly polished by the Tin-Dross.

This is all we resolve to give account of on these sort of Mirrours, for attracting and uniting the Sun Beams. There are many other, as Cylinders, Py∣ramids, whereof we forbear to discourse, since the Authors which have writ of them, have done it with much more sufficiency than we pretend to.

They ascribe the first Invention of Burning Mir∣rours to Prometheus, when he stole the Fire from Heaven to carry to the Earth. Archimedes made ve∣ry happy use of them in defence of his Country, when he burnt the Fleet of Marcellus before Syracuse, by placing his Burning Glass on the highest Turret in the City, whence proceeded such a mighty Confla∣gration, as destroy'd that vast Flota in spight of Neptune and the Waters. Proclus too, a Brave and Famous Mathematician, burnt the Fleet of Vitelian,

that came to Besiege Constantinople; which he pre∣served by this Industry.

Many other Fine and Admirable Relations might be given of the Effects of these Mirrours, but they are too tedious: We shall therefore here put an end to this Chapter, and consequently the whole Book, desiring the Reader to receive all in good part, and excuse the lesser Faults of Impression and Phrase, since we can assure him the Doses are justly prescri∣bed, and the Preparations exact which we have as∣signed.