SECTION II.
Of the apparatus, or fet of
for the preparing and laying on the grounds and colours in enamel painting.
T
HE apparatus neceflary for preparing and uling the feveral fubftances em-ployed in enamel painting, conlifts of a fur-nacc for calcining and fufing the matter of which the colour is compofed; as alfb for burning or fuling the grounds and colours after they are laid on;—of proper muffles or coffins for fecuring the enameled paintings from the injury of the fire while they are burningof pots for fufing the compositions for colours and fluxes, or the mixtures of them together ;—of crucibles for calcining copper and other metals, in order to the preparing the colours;—of mortars of glafs, agate, or flint, and of Hones and muliars of porphyry or flint, for the pounding and levigating the feveral kinds of matter;—of tongs for taking the pots, muffles, &c. out of the fire;—of brufhes, pencils, a fine fearce or fieve. - .
The furnaces for burning enamel are con- ftructed of very various fize or figure» according to the nature and qualities of the work ; and fbme are made to be heated with common coal, and others with charcoal, but at prefent not frequently. The bell form for a furnace for enameling pictures, or other pieces of the fame magnitude, where the dispatch of great numbers are not wanted, is the following; which is made to work with a fixt muffle; in or out of which, the work may be taken without opening the door of the furnace, and annoying the operator with the heat; who, for the fame reafon, likewife may conveniently infpedl the work in the muffle.
The iron-work muft be firft prepared: ■which confifts of a frame and bars, fuch as is defcribed in p. * 5 5 the area of which together muft be ten inches by feven;—of a door and frame, fuch alfo as is defcribed in p. 16, which muft be five inches high and feven long j— and of a plate or ftrong bar to lay over the opening of the front, as below directed, which muft be ten inches long ; with another of the lame magnitude to lay over the door and frame; and one of eight inches to lay over the vent into the chimney;—of a frame for bearing the fixt muffle, which muft fuit the figure of the muffle ; except, that it muft be only three inches in depth, with the back part open, for the muffle to pafs through it into the cavity of the furnace; and that the plate which forms the bottom muft projedt an inch and a half of each fide, beyond the arch or covering, for the brick work to have good hold of it; but this will be better underftood by confidering the form of this kind of muffle, as below defcribed.
The iron-work being prepared, let a chimney of twelve or fourteen feet height be railed; the cavity of which muft be an area of feven <?r eight inches fquare, in the front wall of which chimney a hole muft be left for admitting the lmoke of the furnace. The hole muft be lo placed, that the lower part may be five feet above the foundation of tne chimney; and it may be four inches high and fix Jong: the plate prepared for this purpole being laid over to fupport the brick-work above it.
The chimney being raifed to a proper height, let a pedeftal or foundation to the furnace be built, by adding two walls to thofe of the chimney, fo as to inclofe an area, fifteen inches in depth from the front, and eight inches wide: the front being left open from the default of a fourth wall. This pedeftal muft be raifed four feet and a half high; and then the frame and bars for fupporting the fewel, with their crofs- bars, muft be laid 5 die furthermoft crofs-bar being laid clofe to the back of the hollow area ; or,' in other words, to the wall of the chimney. The plate or flat bar muft be alfo laid clofe to the outermoft crofs-bar of thofe for bearing the fewel, in order that the brickwork may be carried over the hollow area, and inclofe the fquare cavity of the furnace intirely. The brickwork muft be then raifed fix inches higher, in the fame manner as before; only the front muft now be carried up, as well as the fides j which, together with the wall of the chimney, forms a complete inclofed area for holding the fewel: but particular care muft be taken in laying the firft courfe of this brickwork, that the flat ends of the crofs-bars, in which thofe defigned to bear the fewel are faft- ned, be well fecured by the bricks which lie over them. When the cavity for holding the fewel is thus formed, the door and frame muft " be placed in their proper fituation, and the brickwork muft be carried up on the two fides to the level of the top of the frame.: but in the fide moil conveniently fituated, the iron frame for bearing the muffle muft be fixed in the railing this part of the brickwork. This frame muft be placed about four inches higher than the bottom of the door, and two inches from the back or furthermoft part of the furnace j care being taken, that the brickwork have good hold of the parts of the frame formed for that purpofe. The bricks contiguous to the frame fhould be properly Hoped to the hole formed by it, that the opening into the muffle may be wider and more commodious for the taking out and putting in the work to be burnt; as alfb for the more eafy infpeftion of it while burning. The brickwork being brought to a level with the top of the frame of the door, the plate or flat iron bar provided for that purpofe muft be laid over it, in order to fupport the building over it: and the fides of the furnace muft be raifed five inches higher, and the cavity or hollow then covered with a dome of fire-ftone, made a little concave on the inner or under fide, and of any figure the ftone will beft admit on the outward or upper. This dome muft reft bn the brickwork; and they fhould be fo fitted to each other as to make as clofe a joint as pofiible; fo that a coat of fire-lute being laid on the bricks when the dome is put oq, the furnace may be perfectly tight. Windlor bricks fhould be employed for all that of the furnace which is above, the bars for bearing the fewel, and they fhould be laid in Windfor
loom.
Where greater quantities of pieces are to be enamelled, and difpatch is required, furnaces mull be built in the manner proper for containing coffins inftead of a muffle : for the conftruéting which the following is a very good method.
This furnace muft be built till the fabric rife within two inches of the top of the door, in the fame manner as the former ; except with regard to the dimenlions ; and the adding a back wall again!! that of the chimney, which muft be eight inches in breadth, and twenty inches in length. The dimenlions of the cavity oftthe chimney, till it rife to the height of five feet ten inches, muft be twelve inches in breadth ; and feven or eight inches in depth, from the front : and the hollow or area under the bars for bearing the fewel muft be eleven inches and a half deep from the backwall to the front, and twelve inches wide ; and that of the furnace where the fewel is to lié eight inches in depth from the front wall to the back wall, and twelve inches in breadth; to which dimenlions the bars and corfs-bars muft be fuited. The building being carried up to the height here mentioned, a door and frame of the fame form with that for feeding the fire muft be fixt in the moft convenient fide of the furnace ; the intention of which door is to ferve for putting in and taking out the coffins : and it muft there- fore be placed fo that one end of the frame may be clofe to the chimney. The dimen- fions of this door muft be ten inches in height, and eight in breadth. Then the brickwork of the chimney may be proceeded with in the fame manner as before ; except that the back wall againft the chimney muft be raifed no higher ; but the fpace it would take, if carried up higher, muft be added to the cavity or hollow area of the furnace ; the top of this wall ferving as a fupport to the coffins, which are to be placed upon it j only two pieces of fire-ftone of ten inches length, and of the thicknefs of two inches fquare, muft be put with their lower part fixed, at about three inches diftance in the brickwork from the wall of the furnace, that the coffins refting upon them, the flame and heat of the fire may pafs under as well as over them, and heat every part equally. Two vents into the chimney muft be, likewife, made clofe to each fide wall of the furnace j and’may be placed at the height of two inches above the level of the top of this wall, and of the dimenfions of four inches in breadth, and three in height. When thefe lèverai parts have been compleated, and the whole fabric is raifed fifteen inches above the level of this wall, a dome of fire-ftone muft be fitted to it, in the fame manner as was directed fop the former furnace j only it is neceflary, in this cafe, that though the inner or under fide be concave, the upper fhould be flat, for the coffins to Hand upon it to heat, before they be put into the furnace, to prevent their cracking from too fudden an effefl pf the fire.
It is fometimes pra&ifed to burn enamel on a hearth with charcoal; in order to which no apparatus is necefiary but a proper hearth of fire-ftone or bricks, and a fkreen of brick, or feme fuch other material, through which to pafs the nozzle of. the bellows to blow the fire without burning them.
The bellows for this purpofe muft be made in the manner of thofe ufed for chemical experiments, to work with a weight, and to be moved by the operator as he ftands by the fire; but a very fmall pair of that kind will ferve for this purpofe.
Melting pots for fufing the fluxes or colours are indilpenfibly necefiary; the common crucibles being of too looie a texture to contain vitreous bodies, when perfectly liquified. Thefe melting pots are not to be purchafed, but muft be made for the exprefs purpofe. The proper materials are tobacco-pipe clay or Sturbridge clay (which is much cheaper here) two parts, and crucibles ground to powder (or in default of them fine fand) one part; which muft be tempered with water, and well mixed together. The dimenfions muft be regulated by the quantity of matter to be fuled; and the fliape may be a little conical, rather deep than Shallow; to form which a folid mold of wood fliould be procured for working them upon to bring them to a regular figure. When they are formed, they muft be fir ft well dried, and then thoroughly baked, before they be ufed.
Muffles and, where the quantity is great, coffins formed of the fame matter, are requi-, fite for the burning, as well the grounds as paintings in enamel. The ufe of muffles is to preferve the enamel from being injured by me falling of the coals upon it, or by the. fmoke and fumes of the coal, which in many cafes is very detrimental to the colours. The matter of which the muffles may be fabricated may be the fame with that juft now given for the melting pots; and they muft be alfo dried and well baked before they be ufed. The form of the muffles may be of two kinds; the one that comonly ufed : the other a dole muffle fixt in the fire, which is a much more commodious method than the having them loofe.
The fhape of the common muffle is only a flat fquare piece bent into the form of an arch, of fuch dimenfions, that being laid over the enamel work to be burnt, it will cover it. Thefe may be belt made by fpreading the matter properly tempered on a piece of wood, turned to make a round correfpondent to the -arch of the muffle, and working it even on the outfide by a knife or other fiat inftrument j and it may be left on this mold or round piece of wood till it be moderately dry and firm. It is proper alfo to make a bottom to this kind of muffle, on which the plate may be laid : but this may be either a detached part, or joined to it. It is only a flat piece formed of the fame fubftance, and of fiich magnitude as to fu£ ferthe muffle to reft upon it every where,.and, if lode, to have a margin of half an inch for the better taking it out of the fire : but if fixt to the muffle, it need only be of the fame extent with it.
The fixt muffle muft be of the feme general figure with the looife kind; but the bottom mud be always a proper part of it, and exactly of the fize fuitabte to the extent of die arched part, without any margin.
The fize of tnis kind of muffles muft he adapted to the fort of enamel work to he burnt in them : die breadth fhould be fuch as will fuffer the pieces to be eafily put in and taken out; and the height of the arch, where the form of the pieces does not acquire it to he higher, Ihould not be above two inches. The cud of this arch within the fire muff be - cfofed up, fo that when the muffle is pafled through the iron frame in the fide of the furnace made to fupport it* and the joint made good by fire-lute, the hollow or ea- vity of it may be intirely inclofed, except the mouth or opening on the outfide of the furnace. 'The length of this kind of mUffife fhould be fufficient to admit its pafiing five or fix inches into the fire; and yet having a proper proportion remaining to projeft on die outfide fomewbat beyond the iron, frame. But thefe proportions are to bef adjufted by the room wanted. There mud be a falfe bottom likewife made to this kind of muffle, which mult fit the other bottom, fb as tor Aide in find out of the muffle upon it j but. it fhould be made qf fuch length, that when it is thr uft bofne into tfi® muffle, a part of it may pfpjeft ; that proper hold may be always taken for drawing it put, The defign of this fulfil bottom, i* that the enamel work tp be burnt, being hud Upon it, may be put into the muffle eftd taken out without that difficulty and bawd of injury, which would ptherwife refolt from thft form of the muffle.
Coffins for burning larger quantities of pnanad work may be made of the fume matter with the above. The figure Of them may be that of fquare boxes of flee length, when intended for a furnace of the dimen- fions above given, of ten inches; of the hmadth qf fix; and of the height qf feYCft j which measures fhould include aUo the thick- nefs of the fubflance of which they »fe forra-r ed. In the cavity of thefe boxes, Ihrio columns, or projecting parts, fhould be placed a? gainft the fides, riling to half the height of the cavity: ift order that a fquare plate or pkes of the form and fize of the area may be laid them hollow, as a flooring to fupport a feeond unge of layer of the enamel work : and a lid mull be hkewfle fitted to reft in a proper groove made in the fides of the boxes or coffins, at the top of them, that the fire and fmoke may be wholly excluded from the cavity. *
Crucibles of proper fizes muft likewife bo had for calcining the metals; but as they are to be obtained every where ealily, it is need-left to fay more of them. .
; Mortars for levigation mull be likewife had of various fizes j they fhould be either of agate, flint, or glafs; for thofe of iron, or copper, would be liable to deprave greatly many of the colours ; and to thefe fhould be added, a porphyry ftone and muller; marble being too foft to bear the attrition of many of the fub- ftances ufed in enamel, without imparting too much of its own fubftance in confequence of fuchabrafion.
Searces or fieves of fine lawn mull be alfo provided, for fitting fome of the levigated iub- ftances, as alfo for fpreading the powdered enamel to form the grounds: they {hould be like thofe of the apothecaries and druggifts, with a cover and under part for preventing the wafte of the matter, which attends the fining in the open air.
Tongs with points bended at right angles muft alfo be procured, for taking out of the fire the crucibles and melting pots; an iron in- ftrument like a baker’s peel is likewife necef- fary, where the coffins are ufed : the flat part muft be fomething broader than the coffins, and of nearly the feme length ; and the handle fhould be about three feet in length.
To thefe muft be acj^ed brufhes, pencils, tiles, and other common implements of painting : but as they are to be had every where, and their ftrudture is generally underftood, it is not neceflary to be more particular about them,