SECTION III.
Of the general operations fubfervient to the making or preparing colours.
THE operations fubfervient to the making and preparing colours are fublimation,—calcination,—folution, — precipitation,—filtra-
tion,—and levigation.
As the pradhce of moft of thefe operations
is confined at prefent, in a great degree, to the
purpofes of chemiftry; and therefore, very little
under-
3© Of f Hi StfBSTANCtH underftood by any, except thole who concent themfelves in (hat art, 1 fhall endeavour to ex«« plain them, as far as (hey relate to the preparation and treatment of colours; and to give Inch general directions fen* die performng mem, as may take away the «ecefiity of repeating, oft every occafion, thole particulars, which occur hi elmolt all the precedes that partake of the feme nature : but with refpeCt to fuch operas tions, as are more commonly known and prac- tiled, I Ihall only touch on them, in a more general way, without entering into minuter Confiderations regarding them.
Offublimatiott.
Sublimation is the railing lolid bodies in fumes, by means of heat: which fumes are afterwards collected by condenfation, either in the upper part of the fame vellel where they are railed, or in others properly adapted to it for that purpofe.
The end of fublimationis, either to feparate fubftances from each other in order to the purification of one of diem, or to mix them more perfectly than can be effected, without lub- jeCting them to fuch a of degree heat as will necelfarily render them volatile.
The means are, to put the matter, whether fimple or compound, into a proper veflel or fublimer, and there give it a due heat, by placing it in a fand-pot, or the cavity of fome furnace where the naked fire is required : in
doing
» USED IN PAINTING. 31 doing which the following particulars are the moft material objects of attention.
The firft care muft be to provide glaffeS of the hind above mentioned, p. 24, and of a due fize, which muft be regulated as was before mentioned by the quantity of matter to be fub- limed, and by the dimenftons of the fand-pot, or cavity of the furnace where they are to be ufed.
The fublimer uied for making King’s yellow, or for any other operation to be performed in a fand-pot, need no previous preparation. But thole to be ufed for vermilion, which muft be placed in the naked fire, fhould be firft well coated with the fire-lute ; »id a rim of the fame matter muft be worked round the coat at about two thirds of the height of the fobiimer, to fupport it in die iron ring when let down into the cavity of the furnace. This coat of lute fhould be laid on of iiich thicknefs, that it may be about half an inch thick when thoroughly dry: and, if it be laid on at lèverai diftanCes of time, fo that the firft covering of the glafs may be pretty dry before the fécond be put on, it will be the better ; but great care fhould be taken, that the whole be of fufficient drynefs before the fublimer be let down into the furnace j and that the rim of lute fit well the iron rim ; for otherwife ill fuccefs will moft likely attend die procefs of the operation. In default of the fire-lute die following may be fubftituted in its place, for thecoadng fublimers ; and is indeed, on account, of its cheapnefs, moft commonly
ufed j
32 OF THE SUBSTANCES
«fed ; though greatly inferior to the other with
refpeft to the fecurity of the glafles.
** Take of Windior loom, or, if very good, “ common loom, fine fend, and dung of horfes * * which feed on hay, each equal parts. T em- “ per them, with water, or the blood of any ** beaft; and beat them well together.”
In fixing the fublimers in the fand-pots, an inch and half, or two inches of fend, mull be firll put into the pot; on which the fublimer mull be gently fet. The pot mull then be filled with fend up to the brim ; and the matter to bt fublimed mull be put into. the. fublimer, through its neck or mouth ; which mull be afterwards covered by a piece of tile, or flat glafs, laid loofely upon it..
The fublimers ufed without a fand-pot mull be fixed, in the cavity of the furnace, by letting them through , the ring of iron on the top of the furnace, till they hang by the rim of lute. After which the joint formed by the rim and ring mull be made good by pointing with: the fire-lute; which mull, however, be of dryilh confillence; and ufed lparingly, left it moiften the lute of which the rim is made, and, caufing it to give way, occafion the fublimer to flip through, and fall into the furnace.
The fublimers being fixed the fire mull, be lighted; but mull be kept in a moderate degree till the lute be thoroughly baked; when, being increafed, the matter will rife in fumes; and form itfelf, in a cake, on the upper part of -the glafs: and this may be urged forwards by ( railing
USED IN PAINTING. 33 failing the fife, as ftrongly as it will bear to be Without forcing the fumes out of the mouth of the fublimer: which, if it appear to happen, inuft be remedied as quickly as pofiible by a- bating the heat j but proper care muft be taken, that die mouth of the glafs or fublimer be not choaked up by the fubliming matter j for which reafon, the tile, or piece of glafs, which covers it, fhould be lifted up at proper intervals, and an opening made, with the end of a tobacco- pipe, into the cavity of the fublimer. On the neglect of this caution, theglafles are very liable to be burft, by the rarefaction of the fumes, on the fires burning brifkly. When no more fumes arife, which may be known by the a- batement of the heat in the upper part of the fublimer notwithftanding the. fire be equally ftrong, die operation may be concluded to be completed j and, the furnace being fuffered to Cool, the fublimer muft be taken out, and broken j and the cake of fublimed matter in the upper part of the glafs collected: obferving carefully, that it be kept free from the drofs or caput mortuum left in the bottom.
Of calcination.
Calcination is the operating on fubftance«, by means of heat, fo as to produce fome change either in their texture or colour.
Calcination is fometimes performed, by ex- pofing fubftances to the fire with as great extent of furface as poffible: as in the cafe of D lead
34 OF THE SUBSTANCES . lead for converting it into the red lead or minium, and antimony to prepare it for its con- verfion into glafs: in other cafes, it is performed, by putting the fubftances into a crucible, or other fuch velfel, in a more collected body; and furrounding the velfel with fire : and there is a cafe indeed, viz. that of the , mallicot, where bringing it near the fire will be fufficient.
The red lead, red oker, and antimony foT . making the glafs, being calcined in large quan* tides by thole, who make it their foie bufi- nefs, and have large furnaces like ovens con- ftruCted for thefe particular purpofes, I lhall be lefs explicit with regard to them; as it will be fcarcely worth while for any, but thofe who carry it on as a grofs manufacture, to concern themfelves with them, unlefs as a fpeculative experiment.
The calcinatien of other fubftances for the preparation of colours may be performed, by putting the matter into a crucible, and placing it in a common fire; or, where greater heat or room is required, in the wind-furnace defcrib- ed p. 22 where the fire muft be raifed round it; and continued of fuch a degree, and for fuch a duration, as the occafion may make neceflary.
This may be underftood to be all that is re- quifite, where calcination is ordered, in the proceftes below given, without any particular direction for the manner of performing it : but where fuch direction is needful, it will be found to be inferted as each occafion occurs.
. Of
USED IN PAINTING.
3^
Offolution.
By iolution is meant, the reducing any folid body to a liquid ftate by means of another, into which, being put, it is melted or converted itfelf alfo into a ftate of fluidity.
This is performed, by the Amply putting one body to the other and mixing them well together, except in fome cafes, where heat is necef* fary to expedite the effed:.
When therefore bodies are ordered, in the procefles below given, to be diflolved in others, it is only to be Underftood, that they are to be put together, and ftirred, or fhaken, at proper intervals, till the folid body be melted: and where that appears to proceed too flowly, the veflel muft be put into a proper heat fo accelerate the operation: but this heat fhould be always underftood to be lefs than will make water boil, except where the contrary be exprefsly directed.
Of precipitation.
Precipitation is the re-feparating a folid body, from any fluid one in which it is diflolved or melted, by the addition of a third "body, which is capable of producing that eflfed. As, for example, if feed-lac be diflolved in fpirit of wine, and water be added, the feed-lac will be precipitated, that is feparated from the fpirit in which it was diflolved, and reduced to the D 2 ftate
3$ OF THE SUBSTANCES ftate of an impalpable powder, which will fub- fide to the bottom of the veflel containing, the mixture.
- The means of precipitation are .therefore equally Ample with thofe of foiution : there being nothing more required, than to put die matter, which is to fuffer the precipitation, into a proper veflel'; and to add that which is to caufe it; and when the effeft is produced, to feparate the fluid from the folid body precipitated, by pouring off what can be fo parted from it; and draining off the reft in a filter.
Of filtration.
Filtration, though a very Ample operation yet when it is required to be done through paper, and great quantities of fluid are to be Altered, demands feme nicety and judgment in the management of it; otherwife accidents are very liable to happen, which retard greatly the work; and occafion frequently great delay and trouble; efpecially with thofe who are unprac- tifed in it.
As the end of Altration is of two kinds, the one to free fluids from any folid bodies of a feculent nature with which they are mixed, the other to feparate any precipitated powder, or other folid body, from fuperfluous fluid, the means muft be varied. In the flrft cafe, paper, if it be of a right kind, is fufficient; in th* other cafe, a coarfe Annen cloth muft he put
over
USED IN PAINTING. 37 over the paper; otherwife, in taking the filtered matter out of it, parts of the paper will unavoidably mix themlelves with it, and irremediably foul it.
Where filtering through paper is necefiary, the pewter cullenders defcribed p.24. will be found extremely commodious : but great care muft be taken to accommodate rightly the paper to the cullender, as well as to pour the matter very (lowly into it at firft, till it be well fettled, for on negleft of this caution, the paper will be very apt to burl!:,' and delay the operation, by fouling the veflels with the unfiltered matter. If, as frequently happens, the paper, which is prqcured, prove of a bad texture, and want tenacity to bear the weight of the fluid poured into it, or when the fluid itfelf may be of a very relaxing nature, and weaken the paper, a coarfe linnen cloth (hould be always ufed with the paper, whatever the intention of the filtering may be. For, though the fluid will pals falter through paper alone, yet much time will be faved from adding the linnefr by preventing the trou- blefbme accidents that will elfe unavoidably occur.
In filtering large quantities, it will be frequently found, that,' after the paper has been for fome time foaked in the wet, the operation will proceed very (lowly; the fwelling of the fubftance of the paper, as well as the foulnefs of the fluid, diminilhing, and at laft choaking up, the percolating pores of the paper. When D 3 this
38 OF THE SUBSTANCES this is the cafe, the paper fliould be always changed as foon it is perceived, that the filter ceafes to run moderately: for, otherwife, the operation becomes intolerably tedious.
Where great quantities of more ordinary colours «re made, fuch as rofe pink, the kind of Pruffian blue ufed for paper-hangings, or other fuch grofler kinds, the flannel bags mentioned p. 28 may be ufed ; as the filtering fuch great quantities of fluid through paper would be an almoft endlefs labour. In doing this, nothing more is required than to hang the bags on the frames by their loops ; and to feed them with the matter to be filtered: only the firft quantity which runs through; being apt to be foul, muft be returned into the bag, till it be perceived that the fluid come clear. '
Of evapcration.
Evaporation, or the reducing moift bodies drynefs by an artificial heat, where it is not required to be in balneo maria;, may be performed by boiling in any commodious vefiel, till the matter be freed from all humidity; the vefiel being fed with a frefli fupply as the fluid appears to be diminifhed: but in the cafe of vegetable or animal lubfiances, where they are to be evaporated to drynefs, or a thick confluence, as in the artificial gall-ftones, lake or brown pink, it ought to be performed in bal- 8C0 manse; that is, by putting the vefiel con- L taining
USED IN PAINTINÓ.' 39
taining the matter into another filled with water, and kept of a boiling heat : for, by this means, the fubftances are prevented from burning to the veffel as they grow dry which would otherwife unavoidably happen.
The evaporation in balneo maria; may be cbmmodioufly performed in the veflels.I have defcribed p. 27, by fixing the tin boiler in thé furnace, and hanging the pewter veffel in it by the rim j the remaining cavity of the tin boiler, being filled with water, and made to boil till the matter be brought to a proper drynefs or confiftence. * This is all that is requifite where the quantity of matter remaining after the evaporation is large; but, where it is fmall it is better to ufe fbme fmaller veffel; as it would be fo diffufed on the fides and bottom of the pewter one as would render it difficult to be collected. The beft expedient for this, is to ufe a China bafon of a proper fize j and to bang it, by packthread, to two fticks laid a- crofs the edge of the boiler, and fixed, at a proper diftance from each other, by two other fticks tyed to them croffway: by which little machine, the bafon may be fufpended in the boiling water j and, being fed with the fluid to be evaporated as proper room appears in it for a frefh fupply, will perform the office extremely well. But where the quantity of fluid to be evaporated is great, though the remaining matter when dry be fmall, a previous evaporation, by the naked fire, may be ufed till the quantity be properly reduced j taking care, D 4 ter
4© OF THE SUBSTANCES that the matter do not acquire fo thick a confidence, as may fubjedt it to bum to the fidcs or bottom of die boiler.
Of lévigation, and ivajhing over.
Lévigation of colours, where great quanti-* ties are in quedion, is performed in hand and horfe-mills : but this fails to produce ib perfect an effedt, as the muller and done, which is ufed in all other cafes : the aflidance of a pedle and mortar being indeed taken in the cafe of glafs, and hard bodies, to prepare them for the mills or done.
The method of ufing thefe feveral kinds of indruments, as well as the condrudturc of the indruments themfelves, are fo well known, that it is needlefs to dwell on any particulars regarding them : but the other method fubfer- vient to the intention of lévigation, (that is to fay to the reducing pigments to a due degree pf finenefs as powders) called ivajhing over, being lefs generally underdood, and yet of the greated utility for procuring many colours in die mod perfeâ date, I will explain fully the manner of performing it ; which is as follows.
“ The matter intended to be brought, by “ this operation, to an impalpable finenefs, “ being fird well levigated, or, if it be a body f‘ of a chalky texture as the okers, broken to f‘ a grofs powder by pounding, let it be put Î- into a deep balbn almod full of very clean
‘‘ water}
/
USCB IN PA1NTÎKÔ. 41
** water $ and there well ftirred about: then, f ‘ having relied a Ihort time, that the grolfef parts may link to the bottom, let the water, “ together with the finer parts yet fufpended “ in it, .be poured off into another balbn of ft the fame kind j and fufïèred to Hand at reft till the powder has totally fubfided, and left ft the water clear. Let as much of this wa- f‘ ter, as can without difturbing the fediment, “ be then poured back into the firft bafon j and f< let the.flarrixig, decantation, Q?c.be repeated “ as before, as often as lhall be found necef- ft fary to feparate all the powder that is of fuf- ‘‘ fident finenefs. The remaining proffer part ft may be then again ground j and the fame f* treatment continued, till the whole of the ** matter be obtained in that ftatè. This opera- f< tion is, however, in fome cafes, to be re- f* peated lèverai times before the colour can •** be rendered fo perfectly fine as may be “ wilhed : but when it is duly executed, pig- “ ments may be reduced to the moft impal- f< pable powders, with great eafe, even though, ** like vermilion, of the moft obdurate tex- (C ture : and the okers, or any fuch bodies of fc a chalky or clayey texture, which grow foft (< in water, may be freed from land, ftones, or other impurities, and rendered of the higheft “ degree of firienefs, even without any previ- -*■* ous grinding. Where great quantities of “ matter are to be walhed over, as in the cafe ** of okers, common Indian red, &c. tubs muft ‘f be had to fupply the place çf balbns ; and
ƒ* lading
\
42 OF THE SUBSTANCES “ lading with a bowl-dilh muft he ufed inflead “ of decapitation or pouring off.”
SECTION IV.
Of the nature and preparation of par-
ticular colours.
CLASS I. Of red colours.
Of vermilion.
V
ERMI LION is a bright fcarlet pig-
ment, formed of common fulphur and
quickfilver, by a chemical procefs : it is one of
the moft ufeful colours in every kind of paint-
ing; except enamel or glafs; as it is of mode-
rate price, fpends to great advantage in any
kind of work, and {lands or holds its colour
extremely well. It may be prepared in great
perfection by the following procefs.
“ Take of quickfilver eighteen pounds, of flowfrs of fulphur fix pounds: melt the ful- *f phur in an earthen pot; and pour in the ** quickfilver gradually, being alfo gently “ warmed; and ftir them well together, with the fmall end of a tobacco-pipe : but, if <£ from the effervefcence, on adding the lat- ter quantities of the quickfilver, they take “ fire, extinguish it by throwing a wet cloth *e (which fhould be had ready) over the vef*
“ fel.