CLASS II. Of blue colours.
Of ultramarine.
ULTRAMARINE is a preparation of calcined lapis lazuli. It is, when perfect, an extreme bright blue colour, with $ tranfparent effedt in oil, and in fbme degree in w^er; and will ftand, when ufed in paint-ing, without the lead hazard of flying, with whatever vehicle, or pigment, it be mixed. For thefe r^albns, ultramarine is of the higheft va-lue in every kind of painting; being equally Serviceable in all, even in enamel: and though the invention of Pruffian blue, on account of its much lower price, has greatly lefiened the «lie of it, yet this exclufion of it may be con-sidered as an injury to painting in general; as the flues of landfcnapes, and many other parts of modern pictures, fhew the lofs of it, by their changing from a warm, or clear blue, to a feint greenifh or olave teint.
There have been a great variety of methods taught, and pra&ifed, for preparing the ultra- marine. The older methods were, after a calcination in a crucible, to mix a compofttion of pitch, refin, Burgundy pitch, fope, wax, and other ingredients; and to form a pafte of them with the calcined matter; which pafte was then put into water for feveral days ; and afterwards diflolved, by fuccefiive quantities of warm water poured on it, till it let go the colour of the calcined ultramarine j which was
recovered by the fame means as is directed for the wafhing over colours in p. 40. But this method of employing a variety of ingredients, in the cement, was not only unneceflary, but injurious to die colour ; which was never perfedtly freed by the warm water from them: and for this reafon, the methods have been continually varied by thofe, who have attempted to prepare this pigment. I fhall however give the befl of the more modern ; and fubjoin one of older date; which I believe, neverthelefs, to be equally good, though not near io troublefome.
“ Take the lapis lazuli, and break it into * * very irnall pieces, or rather a grofs powder. “ Put it into a crucible; and cover it fecurely “ to prevent the coals from falling amongfl if. “ Calcine it then, with a flrong fire, for an hour “ if there be any large quantity, or lefs time “ in proportion ; and quench it, when taken 4< out of the fire, in vinegar; flirting them “ well together; and fuffer it to remain in that “ flate for a day or two. Pour off then the “ vinegar; except what may be neceflary for “ moiftning the calcined lapis lazuli in grind- “ ing; which operation it mufl then undergo, “ in a mortar of flint or glafs, till reduced to “ the greateft degree of finenefs thofe means ft may effedt; but, if it appear yet too hard to “ be eafily ground, give it another lhort calci- “ nation; and quench it a fecond time in vine- “ gar. The vinegar mufl then be wafhed off from the powder, by the putting to it feve- ff ral fucceflive quantities of clean water; each
of which riiuft be poured off when the lapis lazuli has been wfell ftirred about in them, and “ is again fettled to the bottom. It muft then *{ be ground on a porphyry ftone, with a mul- “ ler, till it be perfedtly impalpable j and then “ dried : in which ftate it is duly prepared to
“ mix with the following cement. Take
“ of Burgundy pitch* nine ounces,—of white “ refin,—and Venice turpentine* fix ounces,— “ of virgin wax one ounce and half,—and of linfeed oil one ounce and a quarter. Mix them ic together by melting in a pipkin over the fire; “ and fuffer them to boil till they acquire fb kt ftiff a confiftence, that, being dropt into wa- ** ter while of this boiling heat, they will not “ fpread on the furfaee of it, but form a “ roundifh mafs or lumps. The cement be- ic ing thus formed, may be poured out of the “ pipkin into the water: and made into cakes “ or rolls for ufe. Of this cement, take ‘‘ an equal weight with that of the calcined lapis lazuli j and melt it in a glazed earthen “ pipkin } but not fo as to render it too fluid. “ Then add to it the calcined matter by very “ flow degrees j ftirring them together with an ivory fpatula till the whole appear perfeft- ly mixed. Being thus mixed, heat the com- " pofition to a fbmething greater degree, and <c call it into a large, bafon full of cold water s and, when it has cooled to a confiftence to bear fuch treatment, knead it well like the u dough of bread, with the hands rubbed over *‘ with linfeed oil, till all the parts be tho- F3 “roughly.
roughly incorporated With each other : fhefi c‘ make the mais into a cake ; which may be ei- “ ther kept till lbme other convenient time in ** cold water, or immediately proceeded with in *( the following manner. Put the cake into ah ** earthen dilh or bafon \ the bottom of whidh “ fhould be mbbed with linféed oil, and pour <( on it water of the warmth of blood : let it ** Hand a quarter of ah hour j and, as the water ** fbftens me cake, it will let loofe the fineft part of the calcined matter : Which, tin <( gently ftirringthe water, but without brfeak- u ing the cake or feparating it into lèflér parts, “ will be fufpended in the water j and muft “ be poured of with it into another veflel. “ The quantity of water muft be then rè- ** newed : and the fame operation repeated'à “ fécond or third time : and, as the mafs ap- ** pears flack, in affording the colour, it muft ct be moved and ftirred, in the manner of *( kneading, with the ivory fpatula, but not ** broken into fragments or fmall parts : and, *c when fo much of the colour is extracted, “ as to render it neceffary for the obtaining ** more, the heat of the water muft be en- “ created to the greateft degree. The-quan- “ titles of the calcined matter, (which is now “ the lapis lazuli,) that were firft walhed ofl^ *• and appear of the feme degree of deepnefs *( and brightnefs, may be put together : and “ the feme of thofe of the fécond degree ; “ the laftwalhings making a third. The water “ being then poured off from each of thefe
“ parcels,
parcels, put on a lixivium formed of two ounces of lalt of tartar, or pearl-alhes, dif- “ folved in a pint of water, and filtered thro’
** paper after the lolution is cold: which lixivium mull be put on boiling hot, and tc the lapis lazuli ftirred well about in it} “ and then the mixture let to cool. The u powder being fubfided, the clear lixivium mull be poured off, -and clean water put in f‘ its place: which mull be repeated till the *( whole of the falts of the lixiviupi are walhed away. The lapis lazuli mull afterwards be dried} and will be then duly pfepared for « ufe.”
“ Another method of purifying the ultra* marine; from the cement may be ufed; which “ is, the pricking the yolks of eggs with a pin, t{ and moiflning the matter to be purified *c with the /oft part that will run out, and ** working them together in a glafs or flint “ mortar: after which the mixture rpuft he “ put into the lixivium j and proceed with as u is above direéled.
“ In order to free the ultramarine from that “ part of the water, which cannot be poured “ off " from it without carrying away part of “ the powder, let it be put in a deep pot, fuch “ as the cups made for coffee} and, after the “ whole is poured off that can be without lofs, “ fet the pot lb on a table or Hand, that fixings “ put into it may hang below the bottom ; “ and then take three or four thick threads of “ loofe twilled cotton} and, having wet them,
put one end of each into the fluid ; and let “ the other, being brought over the edge of “ the pot, hang three or four inches below the “ bottom of it: by which means, the water, “ being attracted by the threads, will drop ** from the lower end till the whole be near- “ ly drained away. The matter may then be ct poured upon a porphyry, or polifhed mar-
ble $ and fuffered to dry.”
The other method, I have propofed to give, differs, from the above, only in the uffng virgins wax and the beft white refln, melted together in equal quantities, inftead of the more compound cement: and this gives up the colour, on its being infiifed in warm water, much fboner than the other.
The other methods of preparing ultramarine differ chiefly in the manner of feparating the colour from the cement and feculencies : which fome recommend to be done, by fqueezing and working the mafs with the hand in warm water, after it has lain in it fbme time to foften. Others advife the putting the mafs in the form of a flat cake, on a board, in a fltuation fomewhat declining from an horizontal pofition, and making water drop on the board above the cake, that it may flow through it, and wafh out the ultramarine: to facilitate which, the parts of the cake muft be frequently opened and ftirred with a flick. But this method is more troublefome and lefs efficacious than that above given.
Ultramarine may be alfo prepared, without any cement, by calcining it j and, when levigated and wafhed over, foaking it in (Milled vinegar made hot. The ultramarine will, in this way of preparation, be produced in greater quantity ; but it will be lighter coloured than when refined by the cement. It is, however, a very good method of preparing it for the Ikies, and fome other ufes.
As it is of the laft confequence to the producing fine ultramarine, that the lapis lazuli, of which it is made, fhould be good, it may be judged of by infpedtion from the deepnefs and clearnefs of its blue colour ; and in order to be more certain of its value, it is proper to heat a finall piece red hot; which, if it retain afterwards its hardnefsand colour, may be accounted good, but if it become crumbly and turn brown, or appear to have fpecks of dulnefs, it may then be juftly fufpetted, or rather condemned.
The different parcels of ultramarine produced from the fame parcel of lapis lazuli, according to the above procefs, will differ greatly in their value: the manner of judging of which muft be by the degree of brightnefs and deepnefs of the colour; but there is no being pre- cifely certain of the worth of any but by comparing it with a fpecimen of known value; and to do that with great accuracy, a little of each fhould be thinly rubbed on white paper, or mixed with white flake and oil, by means of a pallet knife, fo as to form light teints of the fame degree; where the brightnefs will fhew itfelf more dirtinguifhably than in darker.
Of ultramarine ajfes.
Thé pigment called ultramarine allies is the refiduum or remains of the lapis lazuli after the ultramarine has been extracted from it by the a- bovegiven, pr any fimilar procefs. But as the coloured particles which remain are mixt with thole of another kind contained in the lapis lazuli, whether earths or metalline fubftances, thefe alhes mull: of courfe be much lels valuable than even the worft ultramarine : lome- times, neverthelefs, when the operation of the extracting the colour from the calcined lapis lazuli has not fucceeded well, a confiderable lhare of the ultramarine is left behind with the recrement, and greatly-enhances the worth of the alhes: and indeed, as it is certain, that what colour they poflefs when genuine will never fly, they always bear a good price. The appearance of thefe alhes is that of ultramarine a little , tinged with red, and mixed with white * but they are frequently adulterated; and made by the lophiftication to look better than they would in a genuine ftate. This adulteration renders them much lefs certain of Handing, if, as is mod frequently the cafe, it be made by precipitated copper, in the manner before mentioned in the cafe of-the adulteration of the ultramarine. This is ealily, however, detected by the method above given of putting fome of it into a fmall quantity of lpirit of nitre, which, if there be any copper in it will
be tifiged green. But there is another means of fophiftication, that will not render the colour liable to fly : and indeed it is well it is lb, becaufe the difficulty of diftinguifhing it, when not in a high degree, is much greater. This is, the commixing, with the ultramarine alhes, fmalt ground and walhed over : which, when good, and thus treated, has lb much the appearance of the other, that it is fcarcely poffi- ble to perceive any difference by infpeddon. The fmalt'ncvefthelefs, however well ground, will never mix ‘kindly with oil j but fall from it if1 ftltich moiftned, or with lefs oil forms a pafty^matter : nor will it fpread when mixed with white and oil, in any proportion like the Ultramarine afhes. By thefe properties, there- :foft,’'fiif^edted quantities maybe belt judged Of:Jas;the adulteration becomes apparent; if the quantity of the-fmalt commixed with the tree afhes; render them predominant.
The method of preparing the ultramarine afhes is as follows.
*f Take die cement of the ultramarine, which ** remains after the colour is extracted ; and mix xt it-withfbur times its weight of linfeed oil. Let u -die mixture befet in a glazed pipkin over the “ fire; and, when it is thus boiled afhort time, ** pUt it into a glafs veflel, fufficiently large to ** contain it,: of a cylindrical figure: of which “ vfeffel the diameter muft be fmall in propor- “ tion to the length. But care mull be taken, ** that the matter when put into this glafs be ** cobl enough not to endanger the breaking
it. This glafs muft theft be put into a bal- neum mariae; which muft be made as hot " as poffible without boiling ? and kept there “ till the colour appear to be all fubiided to the “ bottom. The oil muft then be poured off “ till the colour appear to rife with it j and “ the remainder, with the colour in it, muft “ be put into another glafs of the fame kind with as much frelh oil as will rife five or fix ** inches above the colour. This glafs muft ** be treated in the fame manner as the firft: “ and, when the colour has fubfided, the oil “ muft be poured off, and a frelh quantity “ put in its place. This having been likewife “ poured off, the colour muft then be well “ walhed, to free it from the remaining oil, firft in boiling water, and afterwards in Tome ** of the lixivium abovementioned made boil- “ ing hot alio. As much of the lixivium be- ** ing poured off, when the colour has fub* (t fided, as can be feparated from it that way, the colour muft be thoroughly freed from <ct the remainder by frequent ablutions with <( clean water. After which die water muft “ be taken off by the means above directed “ for the .ultramarine, till the matter be of a “ proper degree of moifture for grinding. It “ muft then be thoroughly well ground on a “ porphyry j and walhed over j that all the “ harder and infufficiently calcined parts “ may be reduced to an impalpable pow- “ der : in order to which, the remaining “ grolier parts, after the finer have been fepa-rated by the wafhing over, muft be again f‘ ground till the whole be perfedtly fine. The fame means muft be afterwards ufed ** to bring the afhes to a dry powder that were f‘ before directed for the ultramarine.”
Of Pruffian blue.
Pruffian blue is the fixt fulphur of animal or vegetable coal, combined with the earth of alum j and may be made from almoft any a-, nimal, and many kinds of vegetable fubftances; though, from reafons of expedience, it is generally made of the coal of blood only. It is ufed in all kinds of painting except enamel j and is prepared of many different degrees of brightnefs, and ftrength; as well as of different teints: fome parcels being, though rarely, of a true unmixed blue, but the far greateft part of a purple hue; though the proportion of die tinge of red is frequently various, according to the different manner of, or accidents attendant on, the management of it. With refpedfc to ftanding, Pruffian blue can neither be efteemed the moft perfect, nor the moft faulty, colour. When it is very dark, that is, when the tinging particles bear a large proportion to the earth, it will fometimes ftand extremely well; but it is apt then to want brightness, and be very purple: on the other hand, when it is light, or with a fmall proportion of the tinging part, it is more frequently bright, and cool, as it is called, (that 1 is, *
is,, dear of any mixture of red); but extremely fiabjeCt to nyv or to turn to a greyish green. This is not, however, univerial,. for I have feen fome very dark, which has been pretty bright and cool; as likewise feme that has been light, which would {land perfectly well. The common Pruflian blue, however, found in the (hops, which is prepared almoft wholly, at prefent, by ignorant and fordid people, and fold at very low prices, can be very little do* pended upon in paintings of confequence ; but whoever would have this pigment perfect, fhould either prepare k, or procure it to be prepared, in the proper and true manner; and then couriering the high price of ultramarine, and the foulnefs of indico, it may be deemed an acquifition to the art of painting.
The Pruflian blue may be prepared in perfection by the following procefs.
“ Take of blood any quantity; and evapo- lt rate it to perfeCt drynefs. Of this dry blood, ** powdered, take fix pounds, and of the beft “ pearl-afhes two pounds: mix them well “ together in a glafs or ftone mortar; and then ** put the mixt matter into large crucibles or “ earthen-pots; and calcine it in the furnace “ defcribed, p. 22; the top of the crucible “ or pot being covered with a tile, or other ** fuch convenient thing, but not luted. The * calcination fhould be continued, fo long as <c any flame appears to iflue from the matter; “ or rather till it become very {lender and f f blue; for if the fire be very ftrong, a fmall
1 *' flame
“ flame would arife for a very long time*
“ When the matter has been fufficiently cal«
“ cined, take the veflels which , contain it out <c of the fire; and, as quickly as poffible,
“ throw it into two or three gallons of water;
“ and, as it foaks there, break it with a wooden “ fpatula, that no lumps may remain. Put “ it then in a proper tin-vefiel, and boil it for “ the fpace of three quarters of an hour or “ more; and filter it while hot through paper “ in the tin cuilenders defcribed, p. 27; and ft pais fome water through the filter when it “ is. run dry, to waih out the remainder of the lixivium of the blood and pearl-afhes; the “ earth remaining in the filter may be then thrown away. In the mean time, difiblve “ of clean alum four pounds, and of green “ vitriol or copperas two pounds, in three “ gallons of water. Add this iolution gra- “ dually to the filtered lixivium, io long as any ■ ‘ effervefcence appear to arife on the mix- ture; but, when no ebullition or ferment “ follows the admixture, ceafe to put in more. f( Let the mixture then ftand at reft, and a u green powder will be precipitated: from “ which, when it has thoroughly fubfided, “ the clear part of the fluid muft be poured “ off, and frefh water put in its place, and “ ftirred well about with the green pow- “ der; and, after a. proper time of fettling, “ poured off like the firft. Take then of “ fpirit of fait double the weight of the green ,f vitriol which was contained in the quantity
« of
“ of folution of vitriol and alum added to
the lixivium, which will foon turn the green “ matter to a blue colour; and, after lome “ time, add a proper quantity.of water, and “ wadi the colour in the fame manner, as “ has been directed for lake, &c.; and when “ properly wafhed, proceed in the fame man- “ ner to dry it in lumps of convenient fize.”
By the proportions as given in this procefs, if it be rightly conducted, the Pruffian blue produced will be both deep and bright: but where it is defired to be of lighter colour, the quantity of dried blood muft be leflened: for if it be even reduced to one half, a beautiful light blue may be made. The proportion of vitriol may, if only half the proportion of blood be ufed, be alfo reduced to half ; and likewife the fpirit of fait in proportion to that: the only ufe of the fpirit being to rediflolve the oker or iron precipitated from the vitriol. But if any abatement be made in the quantity of vitriol, an equivalent weight of the alum muft be fiibftituted in its place; that there may be a fufficient proportion of one or other of thefe falts, to precipitate the fulphur of the blood from the lixivium.
If the quantity of fpirit of fait preferibed fail, however, to convert the precipitated matter from green to perfedt blue, a greater proportion muft be ufed. For though the quantity directed be fully fufficient, when the fpirit is of due ftrength; yet, as it is frequently found weak when purchafed of the chemifts,
or
or thole who fell it, there can be no certain dependance laid on any rule without ob- ferving that the effect be correlpondent.
Pruflian blue, when made in great quantities, may, for expedition, be dried by heat: and this may be performed by means cf a fmall furnace conftrudted in the following manner. Let a horizontal funnel of brickwork be built, with a vent at one end, opening into a chimney. This funnel mull be of fuch breadth, as will admit its being covered by plates of tin : and its length mull be regulated by the quantity of matter there may be occafion to dry. The plates of tin Ihould be well vamilhed over, as well on the under as upper fide, by drying oil boiled to a thick confillence and black colour; and then rendered again fluid by means of oil of turpentine. They Ihould be cemented to each other, where they join, by putty mixed with the above var- Jiifli: but they may be fixed to the brickwork, which'they rell upon, by fire-lute, and Dutch, or other tiles, laid over the edges. In the front of this funnel, mull be made a fmall fire-place for burning charcoal, which mull vent itfelf into it inllcad of a chimney. The Pruflian blue to be dried mull be laid in the form of a cake upon thcle tin-plates; and then fcored crofs with a piece of horn both ways ; by which means, as the moillure exhales, and the mafs Ihrinks, each fquare, formed by the fcoring, will be a feparate lump Okers, and all other earths, as alfo vermilion, may be
G dried
dried in the fame way on thefe plates: but, as thofe lubftances have nothing gummy or adhefive in their texture, they may be laid on paper upon the plates; which will prevent their contracting any foulnefs from them.
The goodnels of Pruflian blue mult be di- Itinguilhed by its brightnels, deepnefs, and coolnefs: and where thele qualities are found together in any parcel, it may be depended upon that it will Hand well; for whatever is added to it to fophillicate it, or whatever is done amils in the procefs, will always render it more foul and purple. The molt certain way to judge of it is, therefore, to try it with white lead, or flake white, and oil; where the above qualities will difplay themfelves, or appear wanting, in a much more diltinguilhable manner than in the lumps of unmixed colour. In the preparation of the coarfer kind of common Pruflian blue, a great part of the oker or iron precipitated from the vitriol is left in the pigment: but in good Pruflian blue there ought to be no iron. For in time it overpowers the blue of the fulphur of the coal, and Ihews its own proper tinge of yellow in the paint: as.may be feen in ail blue wainlcots, or other work done by houl'e-painters; which in a fhort fpace of time turn to an olive or green- ilhgray colour. The prefence of iron in Pruflian blue may be dilcovered by boiling a linall quantity of what is fulpe&ed in a lixivium of pearl-aihes, to make a feparation of the colour from the remaining earth; which, if it
partake
partake of the other, will appear yellow when wafhed and dried but if free from it, white or gray.
Of verditcr.
Verditer is the mixture of chalk and precipitated copper, which is formed by adding the due proportion of chalk to the folution of copper made by the refiners in precipitating tne filver from die aquafortis, in die operation called parting; in which they have occafion todif- lolve it in order to its purification. Verditcr is, when good, a cool full blue, but without the leaft tranfparency either in oil or water. It is of a moderate degree of brightnefs; and would have confequently a confiderable value in the nicer paintings, where it would fupply the place of ultramarine, or at leaft of the ultra- marine allies, if it could be depended upon : but in oil it is very fubjett to turn greenifh, and fbmetimes black $ and in water, where it is fafer, it is yet not always found to hold: for which reafbns it is rejected, except in paper hangings and other coarfe work, or in varnifh, where this objection to it ceafes.
Verditer is only to be had at a cheap rate from the refiners, who are at no expence in the making it, but that of the chalk and labour, as they could find no other ufe for the folution of copper made by precipitating the filver from the aquafortis, in one of their moft common operations, were they not to apply it to this.
G 2 . The
The manner in which it may be beft done by them is as follows.
“ Take any quantity of chalk, and having “ rendered it properly fine by walking over care- “ fully, add it gradually to the folution of cop- “ per, fo long as any change appears to be pro- “ duced by it from the ebullition excited: or “ the due proportion may be perceived.by the “ fluid’s lofing its green tinge and becoming “ colourlefs. Let it then Hand at reft till the “ fediment be fubfided j and pour oflF the “ clear part of the fluid from the powder; “ adding in its place clean water, which muft “ be feveral times renewed till the falts be in- “ tirely wafhed out; when the fediment, “ which is the verditer, muft be freed from “ the fluid by filtering through paper covered “ with a cloth, and laid out in lumps of a “ middling fize to dry.”
The verditer as commonly found requires no fubfequent preparation for its being ufed : only where, as is frequently the cafe, from ufing chalk in the making of it that is not purified, it is found gritty and not fuflieiently fine, and fhould then be wafhed over.
Thofe who defire to make verditer them- felves, may prepare the folution of copper, by adding copper filings gradually to aquafortis of any kind, or putting plates of copper into it; and then proceeding as is above directed for the refiners iblution. It is not fo expenfive when prepared in this manner, but that it will well
anfwer
anfwer to thofe who cannot conveniently procure that prepared by the refiners.
Verditer is not fubjeCt to be adulterated, as nothing cheaper of the lame appearance can be mixed with it. Its goodnefs mull be di- ftinguilhed by the darknefs and brightnefs of the colour j and that is likewife to be preferred which is of the fulleft blue teint, and not inclining to green : As it may be inferred from thence that the colour will Hand the better. •A much deeper and brighter kind of verditer may be made by ufing a filtered folution of pearl-alhes, in the place of the chalk, and proceeding, as to all other particulars, according to the above directions.
Bleu de Cer.dres, or Sanders blue.
This colour, or rather name, is of late introduction, and has taken its rife, in all probability, from fome French painters having taught the ufe of verditer in water colours "under the name Cendre bleu * which the French in common llyle give to it. This has been corrupted into Sanders blue; and the late writers, who have pretended to teach the art of painting in water-colours, &c. have a- mongft other blunders and abfurdities, Ipoken of this as a diftinCt colour from verditer, known and in common ufe. There is nothing, however, to be found, on the moll diligent inquiry, in the colour-lhops, under this name, but common verditer j or a fpecies of it where the G 3 precipitation
precipitation of the copper appears to be made in part upon ftarch, as well as chalk. But this by no means anfwers the defcription of the author of a pamphlet publilhed by Mr. Peel in the year 1731, who lays, u Sanders “ blue is of very good ufe, and may ferve as “ a lhade for ultramarine or, the blue bice, “ where the lhades are not required to be ex- “ tremely deep, and is of itfelf a pleafant blue'
to be laid between the lights and lhades of “ fuch a flower as is of a Mazarine blue.” By which it is plain the Sanders blue meant here cannot be any kind of verditer; as that is alway^ lighter than- the ultramarine itlelf; and can therefore never be a lhade to it. Un- lels the fpecifcs of verditer mentioned above has been prepared darker than at prefent, as is practicable, and fold under fuch a name, this author mult have made fome miltake; or im- poftd upon the public, by writing what occurred to his imagination without regard to faCt.
If any, however, may delire to prepare a dark verditer of the kind here fpoken of, they may do it in the following manner.
“ Take of the refiners fblution of copper ** made in the precipitation of ftlver from the “ fpirit of nitre; or diflolve copper in fpiiit of “ nitre or aquafortis, by throwing in filings u or putting in flips of copper gradually, till “ all effervefcence ceafe. Add to it of ftarch tc finely powdered, die proportion of one fifth “ or fixth of the weight of the copper diflol-
** ved.
“ ved. Make then a folution of pearl-a/hes, and filter it j and put gradually, to the lb- “ liitlon of copper, as much as will precipi- ** tate the whole of the copper; which may -*f be known by the fluid’s becoming clear and ** cokmrlefs, though before highly tinged with green. Walh the powder, which will be <c precipitated, in the manner directed for ** lake, &c.-, and, when it is fo well drained of water by means of a filter, as to be of a ** proper conftftence, grind the whole well *c together, and lay it out to dry.”
Of indico.
Indico is a tinging matter extradted from certain plants by means of putrefaction, and a coagulation by the air. It is brought from the Eaft and Weft Indies, and cannot, as far as is hitherto known, be prepared in thefe colder climates, on account of the tender nature of the plants which produce it. It was formerly almoft the Only blue colour ufed in painting, either With oil or water, except ultramarine; which,- from its great price, could only be applied to very nice purpofes: but, at prefent, the invention of Pruflian blue, and the foul- nefs of the indico brought from the French or our own plantations, which is greatly inferior in brightnefs to that made in the Spaniffi Weft Indies, which was formerly imported here, have almoft banilhed the ufe of it as a paint, except for paper-hangings, or fuch grofs G 4 ufes.
ufes. Where the beft Spanifh indico, never- thelefs, can be procured, it is preferable for ftiany purpofes to Pruffian blue, of the fame degree of brightnefs, from its certainty of {landing : but it is never found either of the firft degree of brightnefs, nor fo cool as to be fit for all the ufes to which Pruffian blue can be applied.
There is no other preparation neceflary to the ufing indico in painting, except a perfect levigation; to which, for nicer purpofes, wafh- ing over may be added.
The goodnefs of indico may be difcerned by its darknefs and brightnefs: and, as it is always apt to be purple, coolnefs gives a great additional merit to the beft for the ufes of painting.
Of fmalt.
Smalt is glafs coloured with zaffer, and ground only to a very grofs powder. Its texture does not permit it to be worked with either brufli or pencil j but it is ufed for fome purpofes, by ftrewing it on any ground of oil- paint while wet; where it makes a :bright warm blue fhining furface, proper for large fun-dials, and other fuch applications.
It is prepared from fluxing zaffer with glafs 6f falts: the proportion of which may be one feventh part, or more or lefs according to the degree of deepnefs required in the fmalt.
The
The goodnefs of fmalt confifts in its being dark bright and cool, though it always verges on the purple.
Of bice.
Bice is Imalt reduced to a fine powder by levigation. It is a light warm blue colour, and was formerly ufed in oil, more frequently in water colours j but from its unfuitable texture it is now greatly difufed.
Its goodnefs lies in the brightnefs and cool- nefs. This holds good only of the original ^.nd true bice; for at prefent feveral compofi- tions of indico and verditer, with chalk or other cheap fubftances, are fold in the name of bice..
Of litmus, or lacmus.
Litmus is a blue pigment brought hither from abroad, and formed from blue flowers. It is only ufed in miniature paintings, and cannot be there well depended upon, as the leaft approach of acid changes it inftantly from blue to red; though it will ftand if no fuch accident intervene. The original preparation of litmus is by bruifing or pounding the leaves of the flowers, picked off, from the other parts, till they become a pulp; from whence the iuice muil be carefully kept from running off; which juice mull: be afterwards reduced to a dry mais by evaporation in balneo mariae. But
as
as there are no flowers in this country, except the cyanus or corn-bottk, which afford a blue colour, and can be procured in a fufficient quantity, the preparation of this colour is not profitably practicable here, as it can be had from abroad at a very moderate price. The preparation of this colour, previous to its ufe in miniature painting, I fhall give in its proper place, when I fpeak of the commixture of water-colours, with their proper vehicles.
CLASS III. Of yellow colours.
Of King s yellow.
KING’S yellow is a pure orpiment, or arfenic coloured with fulphur. It is ufed for painting in oil and varnifh : and is of an extreme bright colour, and when good a
true yellow j it will likewife Hand well being ufèd alone: but when mixed with white lead, and feveral other pigments, its colour flies or changes. On this account, and for the addi-tional reafons of its being efteemed a poifbn, and having a moft naufeous fmell, it is rejeét-ed by many; but others find too much ad-vantage m its great brightnefs, as well in the ufé of k as a yellow, as when mixed with blue pigments to form a green, not to have recourfe to it on feme occafions.
This pigment muft be prepared by mixing fblphtrr and arfenic by fublimation, which may be done in the following manner.