CHAP. VII.
whites of eggs, ifinglafs fize, and varnifhes formed of gum refins dilfolved in fpirit of wine, or oil of turpentine j which laft, where oil of turpentine is ufed, are called oil var- nifhes.
Gum Arabic has been ufed, diflolved in water, as a varnilh for pictures and paintings, on account of its being both more eafily laid on, and taken off, than the varnilhes formed of lpirit of wine or oil of turpentine. It is more eafily laid on, becaufe it may be made exactly of that degree of vifcidity with which it can be beft worked with a brufli or pencil; and becaufe it is totally free from that accident called chilling, which attends all varnilh made with fpirit of wine. There is, however, a- long with thefe, another quality of fo bad a kind, that its effects more than countervail thefe advantages in the ufe of gum Arabic, as a varnilh for paintings; which is, that as it dries, it is extremely apt to crack; and give fuch appearance of flaws and fcratches, as obfcure and diffbrm the painting to an intolerable degree ; and, therefore, this gum is at prefent much rejefted with refpeCt to this application j and the fubftance we (hall next confider fubftituted in its place. The addition of fugar or fugar* candy will greatly prevent the cracking of gum Arabic j but then it gives a vifcidity or lticki- nefe to the gum that makes the furface of the painting fully, and is in a manner equally detrimental with the cracking of the gum.
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Glair of eggs* beat to an nn&uous, cpofiA-, once, and fpread with, a proper bruih over the, paintings,, anfwers much the fame end *s gum. Arabic: but has the like advantages with much lefs of the bad quality of cracking.: for which region it is generally preferred ta that gum. It has,, nevertheless, one great defeat, which is its not lafting, fork requires to be renewed frequently, as either moifhue or great- drynefs of the air injure it. it is uiual to-mix, arUttle brandy or fpirit of wine with the glatt of the eggs, in order to make it work more; freely with a bruih; as alio a lump of fugar to> give it more body and prevent its crackingy, from which, after all, it will not be intirejy free* after it has feme time laid on, if the picture be' put into a very dry place.
, Ifinglafs fize may be ufe|d for a varnifh in the fame manner as the felution of gum Ara^ hie or the glair of eggs; and if a little honey; or fugar, about a fourth or fifth of the weight of tfie ifinglafs, be added to it, it will cower more, effectually than either of them» and yet be free from cracking. This is not, however, fo tail* ing a varniih as the gum reiins, efpecially if the painting or picture be brought into a damp fi- tuation j and indeed in all cafes it is apt to turn, very yellow with time: but where there is a pro* fpeCt of having occaiion to take off the vamifb for altering the painting, this will he found a very good one j as k may be intirely removed by means of a fponge and hot water.
* There have been many compofitions ki- Werited for lpirit and oil vamifhes for paintings j but the multiplying a number of ingredients in filch compofitions is by no means attended with advantages that are equivalent to the trouble. % wifi, However, give one of the applauded f-ecipes of each kind ; and then fubjoin to it gtfiother more fimple, which I believe will better anfwer the pprpofe.
** Take of gum fandarac half a pound, of
* * Venice turpentine one ounce and half, of the «•* gumsanimi, and copal, each three quarters r* of an ounce, of maftic half an ounce, of Ben- *c jamin, gumelemi, and white refin, each two **■ drams, of reftified fpirit of wine one pound. *c Powder the Benjamin and gum animi; and
* * put to them and the Venice turpentine, con-
tained in a proper fized phial, eight ounces ** of the lpirit of wine j to the copal and refin ** powdered, put, in like manner, in a phial, *c fix ounces 3 and tp die powdered gum elemi ** two punces. Let them Hand, lhaking die *c phials frequendy, till the gum»» be H cfifiolved. Then drain all die dilutions ** thro’ a piece of fine linnen into one bottle j ** and?' after the mixture has flood lome days, decant off as much as will feparate clear; ** and keep it in a bottle well ftppt for ufe.” Some pmit the copal, which is in fa& fo hVfch the fame with the aqimi, that them is no certain mark of diftin&ion known; and pift in its place the fame quantity of gu*H farcqcol: but it is not of any confequense-,
which is admitted j nor whether three parts in four of the ingredients be rejected : for die = following will anfwer the end equally well.
. “ Take of the gums maftic and fandarac,
** powdered grofslv, each fix ounces, of Venice “ turpentine half an ounce, difiolve them in JE=I “ a quart of highly rectified fpirit of wine,«. -, “ and flrain off die fblution as me above. If^fc^f “ this be wanted harder an equal weight of^«f “ the gums anrmi or copal may be added,« -1«
and die quantity of fpirit of wine doubled.”“
In the ufing this kind of varnifh great carets» 'e mull be taken that the pidlure receive nooo damage from it: for the difiolving power die fpirit of wine will fometimes reach the oiK. SI of the painting, and confequendy difturb the_^ c colours.
The vamilh Ihould, therefore, be fpreac^zd with as little and as gentle work of the pencif M\ as poflible j and care Ihould be taken, likewile -=> that the painting be thoroughly dry befbreae the operation be attempted. There is alfb an—— other nice circumllance to be attended to In th-^e jule of this kind of vamilh, which, is to avoi«d what is called the chilling of it; and will certainly happen, if the varnidi be not laid on in a very warm place, or the picture itfelf warmed to a moderate degree: and this will-be flill more liable to happen, if the fpirit of wine employed be not very highly redtified. If tip yarnilh appear to be chilledy (that is when tic parts of the.gums do not attradt each other; but precipitate from the phlegm, left by Ac . , 2 fpirit on its evaporating away, in the form of a powder, which gives a midy turbid appear» ance to the furface, indead of a transparent ihining one,) another coat fhould be laid over it, which will in general remedy the mifchief;- 2nd indeed lefs than two or three coats of this kind of varnilh is not fufficient to prefervc the painting, and bring out due effedt of the co- ours j if ihey are in that date called /»»£ in, >ccalioned by the attraction of the cloth on the >ils mixed with them.
The following is a recipe for an oil of tur- >cntine varnifh of the more compound kind.
** Take of the gums madic and fandarac,
* each four ounces, of white refin two ounces,
* of the gums farcocal, animi, copal, and oli- c banum, each one ounce. Powder them
* grofsly -, and put them into a phial with two ‘ pounds of oil of turpentine j dop the phial, “ but not too fad, led it burd $ and place it “ in any heat; the greater the better, under “ that which will make it boil. Let it dand “ there, till the gums be didolved, or at lead “ fo much of them as will be didolved, then " drain off the folution for ufe.”
The ingredients, except the madic and fandarac, may be omitted at difcretion: and with refpeCl to the gums animi and copal, under which names, a variety of gums brought from the Ead and Wed-Indies, as well as Africa, pafs, there are a very few parcels which will be found to difiblve in oil of turpentine. Indeed I have never found any that would be • P3 fo difiblved: but recipes like this have bcjen given upon very good authority. The follow* ine, therefore, Will be found a much cheapet, lels troublefome, and equally good varnilh with that made by this complex mixture.
“ Take of gum fandarac two ounces, df ** maftic and olibanum each an ounce andhalF; “ or three ounces of maftic, and Venice tur- «* pentine half an ounce: powder them ; and ** diftolve them in half a pound of oil of tur- “ pentine j proceeding as in the above.”
When this kind of varnilh is ufed, it is particularly neceffary that the painting fhould be , thoroughly dry j and the pencil ufed as gently and fparingly in the laying it on as pomble : for the oil of turpentine is extremely ready to diflolve the oil of the painting, if it he the ieaft within its power: on which account the varniihes of this fort are much lefs ufed now than formerly. This varnilh, however, will fpread much more ealily than that with lpirit of wine; and is not fubjed: to chill, even though it be laid on without die aid of any warmth : but it is proper, neverthelefs, to be very careful, that there be no damp or moifture on the furface of the painring j which would prevent the varnilh from taking hold; and wholly fruftrate the intention of it.
Varniihes have been ufed, likewife, formed of the gums fandarac, olibanum, and Arabic, with white relin and turpentine, diflolved in linfeed oil j but they are greatly out of ufe now, as fuch varniihes are flow in drying; and the
liflfeed oil will turn yellow; befides the difad- Vantage arifing from the impracticability of <ver ratine than off the painting again, what-’ <ever oCcanon there may be for it. But a very iccufe and good vamifh may, neverthelefs, be- inade, by difiolving two ounces of fandarac rand olibanum, with half an ounce of Venice turpentine, in half a pound of old nut or ■poppy oil which is white j and if too fat for «other ufe, the better.
All thefe vamifhes muff be carefully laid on *stvith a pencil or brufh, according to the circum- ^itances before intimated to be proper for each ~1ririd : but with refpeft tothofe made of fpirit of wine or oil of turpentine, particular care muff be taken not to pafs the pencil or brufh more than once over the fame place : for, o- vherwife, it will produce ftreaks and inequalities which fpoil the effeCt.
Paintings in miniature are preferred by means of plates of glafs, or the talc called ifinglafs, placed in the frame before them. There is no particular method to be obferved in doing this: "feu* to make die frame fb compact, that the air may have no accefs; which, otherwife, will Ibmetimes prey upon the-colours.
Paintings in frefco, where they are of corv- iequencb enough to merit fuch care, may be tendered more durable;, and preferved from fbcdnefs, by varniflung them with hot fize boiled to a ftrong confiftence, in which a fifteenth or twentieth part of honey has been dif- fblved.
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Paintings in varnilh require no means of pre-
fervation, but from violence} the varnilh itfelf- being a very fufficient defence of the colours againft the air, moifture, or all other fubftances that might effedt them.
Crayons mull: be preferved as paintings with-*ri water colours, by plates of glafs or ihnglals. — s. There have been many experiments made to^~x> difcover a method of varnilhing and giving^^jg adhefion to the colours, to prevent their being^^£.g fo eafily rubbed off, or indeed lhaken off, with^""Kh any very brilk motion: but the fuccefs has notP’«^* been hitherto fuch as makes it material-to com-— municate the particulars of them here.