GL A
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GLA
what Glafs remains, which otherwife would grow green by Continuance of Fire, and fpoil the Glares.
The manner of heating the large Furnaces, is lingular enough : The Tifor, or Perfon employ'd for that purpofe, quite naked to his Shirt, runs round the Furnace without making the leaft Stop, with a Speed fcarce inferior to that of the lighteft Courier : As he goes along, he takes two Billets, or pieces of Wood, cut for the purpofe ; which he throws into the firft Tiffart ; and continuing his Courfc, does the fame for the fecond. This he holds on without Inter- ruption for fix Hours, fucceffively ; after which he is reliev'd b^ another, 2?c It is furprizing that two fuch fmall pieces of Wood, and which are confumed in an inftant, fhould keep the Furnace to the proper degree of Heat ; which is fuch, that a large Bar of Iron, laid at one of the Mouths of the Furnace, becomes red hot in lels than half a Minute.
'Tis computed that a Furnace, before it be fit to run Glafs, cods above three thoufand five hundred Pounds : That at leaft fix Months are requir'd for the building it a-new; and three Months for the refitting it: And that when a Pot of Matter burfts in the Furnace, the Lofs of Matter and Time amounts to above 250 Pounds.
The Glafs, when taken out of the Melting Furnace, needs nothing further but to be ground, fotijh'd, and foliated.
For the Grindi??g of Glass, fee Grinding of Glafs.
For the "Fol 'ifJring of Glass, fee Polishing of Glafs.
For the Foliating of Glass, fee Foliating.
fainting on Glass.
The primitive manner of painting on G/(T/i was very fim- ple, and of confequence very eafy: It confifted in the mere Arrangement of pieces of Glafs of different Colours, in fome fort of Symmetry; and conftituted a kind of what we call Mofaic Work. See Mosaic Work.
Afterwards, when they came to attempt more regular Defigns, and even to reprefent Figures rais'd with all their Shades, their whole Adrefs went no further than to the drawing the Contours of the Figures in Black, with Water- colours, and hatching the Draperies, after the fame manner, on Gla/fes of the Colour of the Object intended to be painted. For the Carnations, they chofe Glafs of a bright Red 5 upon which they defign'd the principal Lineaments of the Face, £S?c. with Black.
At laft, the Tafte for this fort of Painting being confider- ably improv'd, and the Art being found applicable to the adorning of Churches, Bafilicks, &c. they found means of incorporating the Colours with the Glafs itfelf, by expofing them to a proper Degree of Fire, after the Colours had been laid on.
A French Painter of Marfeilles is faid to have given the firft Notion hereof, upon going to Rome, under the Pontifi- cate of Julius II. Albert tDttrer, and Lucas of Ley 'den •were the firft. that carried it to any Height.
The Colours ufed in fainting on Glafs, are very different from thofe ufed either in painting in Gil, or Water. See Painting.
TheSlack is made of twoThirds of Flakes, or Scales of Iron, beaten up, and mix'd with another Third of Rocaille, or little Glafs-beads. — White, with Sand, or little white Pebbles, cal- cined, pounded in a Mortar, and afterwards ground on a Marble; with one fourth Part of Salt- peter added thereto, and the Mixture calcined and pulveris'd over again: To which, when they are ready to ufe it, is added a little Gyp- fum, or Plaifter of Paris well ground, ci?c— For Tellow, they ufe Leaf filver-ground, mix'd up in a Crucible with Sulphur, or Salt-peter ; then, well beaten and ground on a Porphyry Stone; and, at length, ground over again with nine times as much red Oker.— Red is made of Litharge of Silver, and Scales of Iron, Gum Arabic, Harderia, Glafs-bcads, and Blood-ftone, nearly in equal Quantities. This is one of the- moft difficult Colours ; and the Preparation only to be learnt by Experience. — Green, is made of iEs Uftum, one Ounce; as much black Lead, and four Ounces of white Sand, incor- porated by the Fire. After Calcination, they add a fourth Part of Salt-peter; after a fecond Calcination, a fixth Part more : After which they make a third Co&ion before it is ufed.— Azure, Purple, and Violet, are prepared like Green, only leaving out the Ms Uflum, and in lieu thereof ufing Sulphur, for Azure; Perigueux, for Purple ;_ and both thofe Dru"s for Violet. — Carnations are made of Ferretta and Rocaifle : And laftly, Colours for the Hair, "Trunks of 'Trees tkc. are made of Ferretta, Rocaille, &c.
This Account of the Colours we have from Monf. Fell- lien's Excellent Work des c Principcs d" Architecture, Ike. Tho' it mull be own'd that all the Painters on Glafs don't ufe them; there being few Artifts of that kind but have invented their own particular ones, whereof they make great Secrets. But this ascertain, that thefe above defcribed are fufficient for the belt Paintings of all forts 5 provided a Perfon has but the Skill to manage them.
In the Windows of divers antient Churches, Chapels,
Colleges, $£c we meet with the moft beautiful, and vivid Colours imaginable; fuch as far exceed any ufed among us! Not that the Secret of making thofe Colours is loft; but that the Moderns won't go to the Expence of them ; nor take all the neceffary Pains ; by reafon this fort of Painting is not now fo much efteem'd as formerly.
Thole beautiful Works, which were made in the G!afs r houfes, were of two kinds: In fome, the Colour was diffused. thro' the whole Body of Glafs ; in others, which were the more common, the Colour was only on one Side, fcarce pe- netrating within the Subftance above one third of a Line; tho' more, or lefs, according to the Nature of the Colour; the Yellow being always found to enter the deepeft.
Thefe laft, tho' not fo ftrong and beautiful as the former; were of more Advantage to the Workmen ; by reaion, on the fame Glafs, tho' already colour'd, they could fhew other- kind of Colours, where there was occafion to embroider Dra- peries, enrich them with Foliages^ or reprefent other Or- naments of Gold, Silver, &c.
,In order to this they made ufe of Emery; grinding, or wearing down the Surface of the Glafs, till fuch time as they were got thro' the Colour, to the clear Glafs : This done, they applied the proper Colours on the other Side of the Glafs. — By this means the new Colours were prevented from running, and mixing among the former, when the Gla/fes came to be expofed to the Fire, as will be hereafter fhewn.
When the intended Ornaments were to appear white, or filver'd, they contented themfelves to bare the Glafs of its Colour with Emery, without applying any new Colour at all; and it was in this manner, that they wrought their Lights and Heightenings on all kinds of Colours. —
The firft thing to be done, in order to faint on Glafs\ in the modern way, is to defign, and even co'our the whole SubjecT: on Paper. Then they make choice of pieces of Glajl proper to receive the feveral Parts; and proceed to divide, or diftribute the Defign itfelf, or the Paper it is drawn on, into Pieces fuitable to thofe o£ Glafs: Having always a view that the Gla/fes may join in the Contours of the Figurcsi and the Folds of the Draperies; that the Carnations, and other finer Parts may not be damaged by the Lead where- with the Pieces are to be join'd together.
The Diftribution made, they mark all the Gla/Tcs, as well as Papers, with Letters, or Numbers ; that they may be known again.
This done, applying each Part of the Defign on a Glafs intended for it, they copy, or transfer the Defign upon thrs Glafs, with the black Colour, diluted in Gum-water; by tracing and following all the Lines, and Stroaks, as they ap- pear thro' the Glafs, with the Point of a Pencil.
When thefe firft Stroaks are well dried, which happens in about two Days, the Work being only in hjack and white, they give it a flight Wafh over, with Urine, Gum Arabic, and a little black *, and this feveral times repeated, accord- ing as the Shades are defir'd to be heighten'd : With thin Precaution, never to apply a new Warn, till the former is fuf- ficicntly dried. This done, the Lights, and Riiings are given, by rubbing off the Colour in the refpective Places, with a wooden Point, or the Handle of the Pencil.
As to the other Colours above mention'd, they arc ufed with Gum-water, much as in Painting in Miniature ; taking care to apply them lightly, for fear of effacing the Out-lines of the Defign ; or even for the greater Security, to apply them on the other Side, efpecially the yellow, which isvery pernicious to the other Colours, by blending therewith.
And here, too, as in pieces of black and white, particular regard muft be had, not to lay Colour on Colour, or Lay on lay, till fuch time as the former are well dried. It may be added, that the Yellow is the only Colour that penetrates thro' the Glafs, and incorporates therewith by the Fire : The reft, and particularly the Blue, which is very difficult to ufe,' remaining on the Surface, or at lcaft entring very little.
When the Painting of all the Pieces is finifh'd, they are carried to the Furnace, to anneal, or bake the Colours.
The Furnace, here us'd, is fmall, built of Brick, from t8 tor 30 Inches fquare : At fix Inches from the Bottom is an Aper- ture, to put in the Fuel, and maintain the Fire. Over this Aperture is a Grate, made of three fquare Bars of Iron, which traverfe the Furnace, and divide it into two Parts. Two Inches above this Partition, is another little Aperture, thro' which they take out Pieces, to examine how the Co- ction goes forwards,
On 'the Grate is plac'd a fquare earthen Pan, fix or ftveri Inches deep; and five or fix Inches lefs, each way, than the Perimeter of the Furnace. On one Side hercbf is a littles Aperture, thro' which to make the Trials, plac'd direclly oppofite to that of the Furnaces deftined for the fame end.
In this Pan are the Pieces of Glafs to be placed, in the fol- lowing manner : Firft, the Bottom of the Pan js cover'd with three Strata, or Layers of Plaifter, or Lime, pulverized^ thofe Strata being feparated by two others, ot old, broken Glafs : The Defign whereof is to fecure the painted Glafs from the too intenfc Heat of the Fire. This done, the
- R * Gla/fes
