J34 Of THE SUBSTANCES
CHAP. Ill*
Of the vehicles, dryers, and other fubftances ufed in painting for tbfc laying on and binding the colours,
SECT, I. Of the vehicles^ dryeth
See. in general*
T
HE qualities neeefTary in all vehicle* (except in the cafe of crayons) {ire, that they fhould he of a proper degree of fluidty to fpread the colour,-^that they fhould be offuch
a nature, with refpedt to their attractive fition, as fits them to combine well with the coloured pigments:—that they fhould become dry within a due time,—r-and that they fhould be capable of leaving a proper tenacious body j when they are become dry, as well to bind the colours to the ground, as to make them adhere to each other where more than one kind is ufed. But the combination of all thefe neceflary qualities being to be found in no one fubftance, (except oil in feme cafes,) compofitions have been formed to fuit the feveral intentions in a manner accommodated lo each particular occafion. The principal vehicles hitherto ufed are
ails,—water,—fpirit of wine,—and turpentine: but as water, and fpirit uf wine, alone, ’Want the proper undtuous confidence for ipreadihg the colours, and dry away totally Without leaving ahy glutinous fubftance to bind attd fix fuch of the pigments as are of an earthy or incohering texture, gums,—fize,— fugfir,-1—4nd Other fuch vilcrd fiibftances have been fiiperadded to fupply the defeats and render thertt of due confidence and body.
Though oils limply fifed are a pcrfedt vehicle of colours in lome cafes; yet in many Others, haViiig been found to dry too llow- *?> fllOarts have been fought after, by the addition Of other bodies, to alter this quality in fuch as may be defective in it; which hak tttorifeqtifently introduced another kind of fub- ftancfis ihto the materia pidtoria ; that from their being employed in the intention of remedying this fault in the oils, of not drying lufficientiy felt, are called D R Y E R S. Thefe are eithfer ingredients of a different nature added tb them, without any preparation of the oils j or part of the oils themlelves, into which this quality has been introduced by the operation of heat, either in their fimple Hate, or with the addition of the other drying ingredients : which oil, thus changed, being thence rendered capable on its commixture with other oil* to caufe them to dry falter, is called drying bil j and frequently ufed in the fame intention as Other dryers.
As water in its fimple Hate is for the molt part incapable of being a vehicle to colours, they being in general of an earthy or incohering texture, it is neceflary to give it a more vifcid confidence, and to join to it a body which will dry with fuch a tenacity as may bind the colours« This is done by adding gums, fize, fugar* or fuch other bodies as tend to infpiflate and impart to the water a more clammy and thick confidence. But where the colours themfelves are bodies of a gummous nature, and will difiolve or grow vifcid in water, as gamboge, the juice of the buckthorn berries, of of the French yellow berries, , and fuch others, further admixture, in the intention of a vehicle* is needlefs, and tends only to weaken the effedt, or foul the colours.
The mod ufual addition where water is ufed in nicer paintings, is the tranfparent gums, fuch as the gum Arabic, and Senegal: and the principal reafbn of their preference to o- ther bodies, which render water vifcid and glutinous, lies in their differing the mixture made of them with the colours to be indantly reduced to a working date, by the addition of frefh water, at any time, though the quantity originally ufed be intirely dried: by which property in the fubdances employed to infpid fate the water, colours fo prepared may bfi kept in a condition ready for ufe in fhells, oi other proper veffels, to any length of time But the gums have, neverthelefs, a very untoward quality, when mixed with mod kind; of pigments, which is their being very liable to crack and peel off from the paper or vellum on which they are laid. To remedy this, therefore, fugar candy, or what is better, though feldomer ufed, honey is frequently added to them; and by iome ftarch, boiled flower, and other bodies of a like nature.
The painting in this kind of vehicle is call-' ed painting in water colours, and from its being of late moftly confined to fmall objeds* miniature painting: though it was till the in- trodu&ion of the ufe of oils, which is modern,; the only common method of painting in any1 way, fince the encauftic and other methods of - the antients have been loft.
For grafter paintings and purpofes, water is rendered a proper vehicle by the admixture of . lize; which is free from that difadvantage of cracking and peeling, that attends the ufe of the gums: but then, on the other hand, it is unfit for nicer purpofes, where only a fmall quantity of each kind of colour is required. For as the compofitions of the vehicle and colours do, in fuch cafe, foon become dry, and thofe mixt with fize when once dry will jiot again commix with water, by rubbing with a brufh or pencil, as thofe compounded with the gums, it would be endlefs to employ fize for fuch purpofes j as all the kinds of colours muft be frefh ground up and prepared every time there may be occafion to ufe . them. The painting with fize is, therefore, confined principally to fcenes, and fuch large works; where it is now called frefco painting, I fuppofe from its having been at firft moftly ufed for filch pieces as were intended to be placed without doors.
There are like wife particular cafes where o- ther duid fubflanees may be employed âdvâri- tageoufly along with the vehicles formed by water ; as in the cafe of verdigrife, where wa- <. ter failing to diflblve it, vinegar, or juice of rue, as was before mentioned, Ihtmkl be fob- ftituted in its place : but they are in fâét only: natural compounds of water, and what may be wanting to make the pigment diffolve in, . or commix with it.
Spirit of wine, as a vehicle for colours, is litefr- wife infufficient to the end without being compounded with other fubftatices : as it wants à proper thicknefe or vifcidity, either to fufpeftd the pigments, or to bind and fix them to die ground when dry. It is, therefore, found neceffary to difiblve in it filch gummous àt refinous bodies, as feed or fhell lac, maftid, fanderac, or refin ; which anfwer thé famé purpofe here, as gum Arabic in water. A vehicle, however, formed from this mixture, has fome advantages over all others j as the colours are fo defended by the gummous or refinous bodies, that the moft tender kinds {land very well; and retain their beauty to any length of time, if no violence impair them. The ufe of this kind of vehicle is called painting in varnijh ; which art has been greatly improved and extended within thefe few years, by the manufacturers at Birmingham ; and will probably hereafter, when the conveniences cnees and advantages of it are more generally known, be applied to purpofes of greater account, with refpedt to the fpecies of painting.
It has been lately a practice with fome e- minent portrait painters, to make a compound vehicle by mixing oils and varnifh together: and this likewife is, by them, called painting in var- nijh-, though it ought, I think, rather to be called painting with varnijh. The advantage that has principally induced them to ufe this method, is the quick drying of the colours, which is the refult of it: but time will Ibew them another yet greater advantage in it; I mean the prefervation of the colours, to which it will greatly contribute. The varnifh ufed for this purpofe mull be formed of oil of turpentine : but the particular compofition we lhail have occalion to fpeak of below.