USED IN PAINTING. IJ mills, ftones and mullars—with lèverai other lmaller implements fubfervient to thefc.
As lèverai of thele implements are in common ufe for other purpofes, and confequently to be had ready made of a proper conftruc- ture, I {hall only enumerate them, without entering on any particular delcription of them: but with refpeCt to that part of the apparatus, which relates to the more fecret arts of making feveral of the colours, and has any thing peculiar in its fabrication, I will endeavour to give ltich a conception of the proper figure of every particular, and fuch directions for their con- ftruCtion, as may enable any to procure them to be made by proper workmen. As, without this previous information of the necefiary me»» of performing them, the giving the recipes or procédés alone for making the colours would be of very little confequence : and as, by this method, I avoid the neceflity of repeating frequently the inftruCtions for thofe particulars, which when given in a more general way will ferve effectually for a multiplicity of occafions.
Offurnaces.
The furnaces are of the moil difficult con- ftruCtion of any part of the apparatus for making colours ; being mod: remote from common experience and conception : and yet it is indilpenfibly requifite, that they fhould be completely adapted to the purpofe they are intended for. I {hall therefore be molt particular in my directions concerning them : but,
before
before I enter cun that tafk, it may be pitv** oufly neceflkry, to teach the manner of mak-* tag a compofitkm, which I fhall have occ^fion 10 dtreft me ufe of frequently in my inftruc« tic ns foe the building them, at vrdl as on Other occafions. I mean the lute for making good the junctures that fuller a great heat, and ftcuring bodies of a tenderer nature from the effe&s of the lire j which I fhali call here, as is done ellewhere, the fire-lute: the cotnpofi-* don of which is as follows.
** Take of green vitriol, or copperas, any . “ quantity; and put it into an earthen pipkin, ** of which it may fill only three parts, and “ fetit on a common fire; taking care that it ** may not boil over} which will be very lia- “ ble to happen if the fire bum too brifkly* ** When it has almoft done boiling, throw in “ more of the vitriol, the quantity at firft M thrown in being now (hrunk and contrail« ** ed ; and let that alio boil to drynefs $ and " repeat this till the pipkin be near full of the “ dried matter : raife the fire then round it; “ and let it continue in as ftrong a heat as can * be conveniently made, till the whole contents M become of a red Colour; alter which take it out of the fire j and, being cold, break the “ pipkin, and feparate the calcined vitriol from H it. Take then of this calcined vitriol pow- 44 dered two parts, of the fcoria or clinkers of st “ finith’s forge, finely levigated,—Sturbridge « clayorWindfor loom dried, and powdered,— ** and fine fond, each one part; mix them well
“ together^
“ together; and then temper them, with the “ blood of any beait, till they become of the “ confidence of mortar a twentieth part of “ the weight of the whole of ihort hair being “ beaten up with them.”
The furnace for vermilion, as well as the operation to be performed in it, are of the moil nice nature of any objects relating to the art of making colours: it is indeed fo difficult a thing to manage well the manafa&ure of ver- million,that his given up in general in this coun* tty, even when the price of quickfilver would make it very profitable; and me greateft part, if not the whole of tjhe confumption, is iupplied from Holland: but if any trail prepare well the apparatus as here directed, and execute properly the procefs given below, they need not doubt, with fome experience, but to be able to carry on this manufacture as well as the Dutch. The manner of conftru&ing the furnace may be as follows.
The firft itep mult be to procure the proper iron-work, which confifts of bars for bearing the fewelji—a frame,—doors for feeding the fire,—a ftrong plate for fupporting the brickwork otter them,—an iron frame and hopper for feeding the fire,—and an iron ring for laying over the top of the furnace, for the better hanging the bodies or fubliming veflels in it.
The bars Ihould be of hammered iron, eight in number, eight inches in length, a quarter of an inch in breadth, half an inch in depth, and fixed firmly by each end, at the dihanoe 1 of
of a quarter and a half quarter of an inch front each other, into two ftrong crofs-bars; which crofs-bars muft be fuffidently long to admit of their fuffering the brickwork to have good hold of themj and muft be made flat at their ends, on that account.
The frame and door muft be alfo of hammered iron. They muft be of the length of the area or fire-place as formed by the bars; but. need not be more than four inches high. They may be of the ufual form of! thofe made for the furnaces of coppers, but ftronger j and it is better to have the latch bigger than is common, and carried acrofs the whole door j which will give it ftrength to refill the weight of the fewel, that, otherwife, when the iron is fbftned by violent heat, is apt to force the middle part outwards.
The iron bar to lay acrofs the frame of the door may be three inches in breadth j and d- bout three inches longer than the frame itlelf: it may be either of call qr hammered iron, as lhall be found moft eafy to be procured.
The frame and Hopper for feeding the fire fhould be alfo of hammered iron : the frame may be four inches long, and three inches high. It may be formed of four plates of a moderate ftrength j of which thofe of the top and bottom muft Hope downwards towards the fire in a parallel; they muft alfo project beyond their joining with the fide plates j in order to their being fixed in' the brickwork. The Hopper muft be formed of five plates, put
together
, together in fafhion of a box; (as in the doors of portable iron furnaces;) and of fuch figure and proportion, as to Aide into the hole formed by the frame, and fill it up exactly, fb as to render that part of the furnace intire, when it is not taken out occafionally to feed or ftir the fire. The hollow of this box or ftopper mull be turned towards the fire; and filled with fire lute; and a handle mull be fixed in the middle of the outward part, for the more commodious ufe of it when hot.
The iron ring for hanging the bodies or lub- liming- veflels in the fire muft be made of caft iron. It fhould be of about four inches depth, and of a conic form, converging outwards. It fhould have an outward rim, or margin turning off from the ring horizontally; in order to its lying on the brickwork of the furnace. The diameter of the ring muft be in proportion to the fize of the fublimers to be hung in it: it fhould be about two inches wider in the lower part than their diameters; and muft diverge or inlarge itfelf upwards half an inch.
The iron work being thus prepared, and a proper quantity of Windfor bricks, and the loom they are made of, or Sturbridge clay, as well as common bricks, and coal-afh, and common mortar, provided, the dimenfions of die furnace muft then be thus fettled.
Take the diameter of the greateft fublimer intended to be worked in it, and add to it two’ inches to allow for the lute, if any fhould be ufed round it; then add twenty-two inches, and
C it
it will give the diameter of the whole area of
the furnace.
The dimenfions of the furnace being thus fettled, the ground plan muff be made in the following manner.
A round of bricks muft be laid of the diameter of the area of the whole fabric as fettled above, and the barsmuft be laid in the center of it, in their proper poiition; and a line drawn dole at the back of the furthermoft crofs-bar, which mull begin a quarter of an inch beyond the infertion of the outermoft of the long bars on one fide, and extend to a quarter of an inch beyond the outermoft bar on the other fide. From the extremity of this line, two others muft be drawn, parallel to the tides of the outermoft bars, and extended to thé circular line which marks the area of the whole fabric. The ground’plan being fo marked, a cylinder of brickwork muft be raifed in this circle, leaving a hollow fquare within the lines formed as above for the area of the fire-place and afh- hole. This cylinder muft be carried up about eight inches j and may be built of common bricks and coal-afh mortar: but they muft be laid folid, that the whole mafs may not fhrink when fubjedted to a great heat. When this cylinder of brickwork is raifed, the bars of the tire place muft be laid over the innermoft part of the vacuity left for the afh-hole j and the door, with its frame, muft be alfo placed in their proper pofition, in the front of the bars : which will not be, in this manner of
eonftru&ion, on a level with die exterior fur- face or front of the furnace, as in thofe of th« common kind, but dnly half the length of th« bars from the center of the whole furnaces* The brickwork muft be then again carried up fix inches higher, in the fame manner as before 5 only it muft be made to take proper hold both of the crofs-bars of the fire-grate and the frame of the door: but, in this part öf the fabric, the courfes next the fire fhould be of Windfor bricks ; and laid in Windfbr loom, or Sturbridge clay.
The fabric being railed to this height, the iron plate prepared for that purpofe muft ber laid over the opening of the brickwork, from the top of the door frame to the exterior fur- face of thé fabriek: that the brickwork may be carried intirely round above: and the cylinder of brick muft be again proceeded with a9 before j only it muft be now continued intirely round, forming only an area in the middle ; which muft be made Hoping from that which Is to hold the fewel j and muft inlarge itfelf in fuch manner, that, in railing the furnace eight inches higher, the diameter of the cavity may be equal to the diameter of the fubliming vef- ffel, with the addition of fix inches, to allow for the fpace in which the fire muft come found it on each fide.
In the laft courfe of bricks which raife the fabric to this height, the whole muft be left for fixing the frame that is to form the opening for feeding the fire; which muft be aefcord- C 2 ingly
ingly placed in it, in fuch manner, that the Hope formed by the upper plates, which compofe it, may incline towards the fire. The proper fi- ■ tuation for this hole is in the front of the furnace, over the opening leading to the door of the afh-hole.
From this height the brickwork muft be carried up, forming a hollow cylinder, for four inches more ; when a courfe of bricks, of which the inner ends are cut Hoping, muft be laid fo as to contrail the circle of brickwork to the diameter of the iron ring for fupporting the fublimer; which muft be then let into this opening left at the top of the furnace, and fixed with fire-lute; the bricks furrounding it being well pointed with the fame. This part of the furnace, from the fire-place to the top, fhould be intirely built, of Windfor bricks, laid with Windfor loom or Sturbridge clay.
In the laft courfe of bricks muft be left an opening of four inches length, for venting the fmoke into the chimney: over which opening, an iron plate muft be laid, and carefully pointed with fire-lute; that the air may have no accefs to fpoil the draught. The chimney may be a- bout fixteen or eighteen feet high; and the hollow about fix inches fquare, or. of an area e- qual to that; and need not be built of a greater thicknefs of bricks than is neceflary jn order to its fupporting itfelf.
• The furnace for fubliming King’s yellow; muft have a land-pot; as the heat of the naked fire would be too great.; This pot may .2 ~ be
Be of a greater or lefs fize, according to the quantity of the King’s yellow prcpofed to be made: but, where there is no particular convenience in varying from it, the ordinary fize will be found moft commodious.
The land-pot being procured, as likewife the reft of the iron work, according to the preceding directions given for the furnace for vermilion, except the iron ring for the top of the furnace, which in this cafe muft be changed for a flat rim of caft iron of four inches breadth,' with a groove to receive the pot, and fupport it hanging in the furnace, the plan of the furnace muft be made out in the following manner. The diameter of the pot being firft taken, fix inches muft be added to it, for the cavity to admit the fire to come round the pot, and the length of two bricks to allow for the thicknefs of the fides of the furnace : thefe being put together give the diameter of the whole furnace. To find the due height, the depth of the pot muft be firft taken ; to which muft be added ten inches for the diftance betwixt the pot and the bars ; eight inches for the diftance of the bars from the ground, with the height of a brick, for a courfe that muft be carried round the edge of the pot; which, being all put together, give the height. The building may be then carried on, in the lame manner as was before advifed for the furnace for vermilion, till all be completed but the laft courfe; and the rim muft be then laid on the top of the brickwork, and well pointed with fire-lute: after which, when thefe part? of t
furnace are fo dried as to hold well togeth the pot Ihould be let down into the furna<where it will hang by its margin or turn edge, refting on the groove made for it in t
iron rim : and another courfe of bricks m then be raifed, in a continued line with I fides of the fand-pot, that part of them whitouches the pot being laid in fire-lute.
The furnace for calcining the Pruflian bli oker, ultramarine, C$c. may be conftrudted the following manner. Firft prepare a let bars, which may be a foot in length, and f
teen in number, with a ftrong frame and d<pf which the breadth mull equal that of 1 bars, and the height be a foot, as alfo a plaor two ftrong flat bars, to fupport the brie
work over the door frame, and another fupport the brickwork oyer the alh-hole.
foundation or pedeftal of bricks mull then raifed, about three feet and a half high, a two feet four inches fquare j which may done with common bricks and mortar j
need only, indeed, be four walls j the holl<formed by which may be filled up with n bilh, and floored over with bricks or tiles. <
this pedeftal, raife three other walls ; one each fide, and one at the forthermoft end, the whole brick thicknefs, forming an area 1
twixt them, of the length of a foot, and the breadth of ten inches ; of which area 1 front will neceflarily be open from the defa pt tfcc fourth wall. Oyer this opening, in i
front, lay the bars in the center of tl?e brickwork} and place alongwith them a plate, that will reach from their edge to the extremity of the furnace, to bear the brickwork which mufl lie over that part of the hollow. Then carry up the fides as before, but with four walls in- flead of three, to inclofe the area of the fireplace intirely} taking care, that the firft courfe have good hold of the flat ends of the crofs- bars.
This part muft rife eight inches above the bars: and then the door and frame mufl be fixed} and the other fides carried up as before.
When the building is carried to the height of the door and frame, the ftrong plate muft be laid to bear the brickwork over it: and the hollow muft then be made to converge, till it become fo narrow as to form a chimney: of which the area of the cavity may be fix inches fquare} or it may be turned into a funnel, or flew, to communicate with any other chimney, if fuch there be fufficiently near. But, as the wind-furnace demands a very confiderable draught, if the flew be made from it into the chimney of any other furnace, which may not happen to be at work when there is occafion to ufe this, care muft be taken to flop the chimney of the other furnace, below the ad- miffinn of this flew into it, to prevent a falfe draught which would otherwife intirely de- . ftroy its effects on the wind-furnace: and for this end, regifters fhould be always put to the' AswS|Or chimneys below where the flews enter, ViJt; ' C 4 <>f
of each furnace, whenever two or more vent themfelves into the fame common funnel.
Sublimers muft be of glafs, and may be generally had ready made of a proper figure at the glafs-houfes, where glades are blown for the common chemical purpofes. They muft be inquired for under the name of bodies, or cucurbits; which name they bear when applied to medicinal ufes. They Ihould be cho- fen of a fpheroidal form; neither the conical lhape in which fome, nor the oval in which others are made, being fo commodious for fub- liming colours, as a longifh Ipheroid : but, where they cannot be obtained of this figure, an oval may be difpenfed with.
The magnitude of the fublimers muft be determined by the quantity of matter to be fublimed; and the dimenfions of the furnace: but thole ufed in fand-pots fhould be always at leaft two inches lefs in the diameter than the pot in which they are to be placed: and thole ufed in the naked fire Ihould never be more than four inches lefs in diameter than the iron ring of the furnace in which they are to be hung.
Where vermilion is made in great quantities, earthen fublimers are ufed ; but we fhall lpeak of them in their proper place.
A pewter boiler is neceflary for boiling cochineal, brazil or other woods, French berries, &c, for making lake, brown pink, Pruffian blue, and many other pigments. It is requi- fitc that this metal fhould be ufed for it, be-
caufe
oufe iron and copper, as they will neceflarily be corroded in a greater or lefs degree by the (aline fubftances requilite to be ufed for making feveral forts, are extremely injurious to the colours ; and fhould, therefore, never be fuffered to approach the finer kinds.
The form of this boiler may be cylindrical, with a bottom making a fedion of a fphere. Its dimenfions may be three feet in depth, and one diameter: but this may be varied, as the quantities of colours propofed to be made may vary the occafion. At the height of about two feet, muft be joined to it, a ftrong margin or rim, by which it may be hung in the furnace ; and a little above, muft be two bow handles oppofite to each other, by which it may be lifted in and out of the furnace. The whole muft be wrought ftrong j as there will be frequent occafion to move it, when containing a confiderable quantity of fluid.
The furnace for this boiler muft be con- ftruded in the following manner.
A rim of iron, fuch as was before directed to be ufed for hanging the fand-pot, together with die other iron-work, muft be firft procured, The diameter of the boiler being taken, as alfo its depth below the rim by which it is to hang, the proceeding in the fabrication may be the fame as that of the furnace for the fand-pot, till the iron rim is to be fixed ; when the courfe of bricks, which is raifed upon the rim in that kind of furnace, muft be in this wholly omitted. It is not improper, however, to allow two inches
more
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bloom or filtering paper : but care mull be taken in the choice of it; for it is difficult to find, in common ftationers (hops, luch as will even moderately well anlwer the end.
For coarfe colours, fuch as role pink, flannel bags may be employed, for expedition. They mould be made in the form of pudding bags i and are called, when applied to this pur- pole in medicine, Hippocrates’s lleeve. They ihould have proper frames for fixing them j which may be made of three Hicks or wooden rods, fixed together at fuch a diftance, that the bag, being hung upon them by three loops fallned to it, may have its mouth or opening fubtended to a due width for pouring in the matter to be filtered.
Long boards mull be likewife provided for drying colours. They Ihould be made of found wood j and very well plained, and it will be yet better, if the furface be made frill fmoother, by varnilhing them with feed lac.
Chalk-frones are alfo proper on fome occa- fions, for expedition, for the drying ultramarine, Pruffian blue, walhed okers, and feveral other kinds: but they mull never be ufed for lake, carmine, or any colours made of vegetable matter; for their alkaline quality of chalk may .be very detrimental to fuch colours. Where Pruffian blue is made in very great quantities, there is a particular apparatus ufed for drying it: but we lhall lpeak of that in its proper place.
The
The lévigation of colours, being of the moft general ufe of any operation, is likewife required in many cafes to be moft perfectly per* formed; and, therefore, proper inftruments fubfervient to it are extremely requifite. Hand- <nills, and fometimes even horfe-mills, are ufed for groflèr forts of pigments, or where very large quantities are to be difpatched : but, as they are to be had of the proper workmen, duly conftrulted, it is needlefs to defcribe them here. The muller and ftone are gene*, rally ufeful; and fhould alone be depended on, at leaft for completing the lévigation after the grinding them in the mills, whenever the colours are of any greater , value or nicer ufe. Bafons fhould likewife be provided for walh- ing over the colours according to the manner below defcribed.