SEC T I O N VI.
Of the fubjlances ufed to render fpirit of wine a vehicle for colours.
Of feed lac.
SEED lac is a fubftance formed on die boughs of trees by fmall flies, as theif nidus or habitation. It difiolves in fpirit of wine; and being left dry again, by the eva-poration of the fpirit re-attains its original hard and tough texture. It is therefore extremely beneficial in defending and fecuring colours from any injuries, the air or flight violence
might do them: but the brownnefs of its co-lour, and its not rendering the fpirit of wine in which it is diffolved of a confiftence fuffi*ciently thick and vifcid to fufpend the pow-
dered pigments when they are commixed with it, are defeats which greatly deftroy its value as an ingredient for making fpirit of wine a proper vehicle for colours. It may, however, be improved for this purpofe by the addition of turpentine, and other fubftances: as we fhall obferve in its due place.
The goodnefs of feed lac confifts in its ap-proaching towards,a tranfparent colourlefs ftate, and being free from heterogeneous matter and opake parts: for, as the brownnefs is its great-eft defedt, the diminution of that quality conse-quently inhances its value.
The preparation of feed lac, for mixing with thefpirit of wine, is to pick out, or wain from it by nieans of water, all the little woody or other feculent parts ; and then to powder it grofsly : for if it be reduced to a fine powder the whole will run together, and cohere, fo as to hinder the fpirit of wine from commixing with the particles and difiblving diem. Thefe who want feed lac for ufing with, opr lours, where whitenefs or brightnels are demanded, muft pick out the lighteft coloured (trains; and ufe them only; reserving the nrowner for coarfer purpofes.
Of Jheil lac*
Shell lac is, a fubftance brought hither in ■very thin pieces ; and partaking greatly of die Mature of feed lac : from which nevertheless -it differs fo much in fome properties, as clearly dhews they are not the fame fubftance under a ■different form, as has been fuppofed by many. ^Shell lac diffolves in fpirit of wine as well as deed lac ; but never becomes perfectly clear — wild tranfparent. To compenfate however for this defeat ; it renders the fpirit much more ■vifcid, and capable of keeping the colours fu- Ipended : from whence it derives a confidera- hfe value in this kind of painting.
The goodnefs of fhell lac eonfifts in its approaching to tranfparency and whitenefs, but -it is never found without a great degree of fcrownnefs. There is no more preparation of
fhell lac than feed lac required previoufly to its being ufed for this purpole with ipirit of winej the. reducing it to grofs powder being thfc whole.
Of tuff entint.
Turpentine is capable of diffolving in ipirit of wine, and giving it a vifcid confidence 5 on which account it is fometimes ufed along with other bodies to render the fpirit a fit vehicle for colours. A compofition formed of it with maftic, fandarac, refin, and in feme cafes feed lac, will ferve for purpofes where the painted body is not fubjedt to great rubbing, or any violence : but with refpedt to hardnefe aAd durablbnefs, all fuch compofitions fall-far ihort of the felution of ihell lac. : - <
Turpentine muft be chofen by its clearaefe and purity: and requires no preparation previ* ouily to its being applied to-this purpofe.
Of the gums majlic and fandarac.
The maftic and fandarach are much of the lame nature; and applied to the fame purpofes with regard to painting. They are gum refins intirely white and tranfparent when good j and diflolve perfectly in fpirit of wine : on which accounts they are ufed for rendering Ipirit of wine a vehicle for colours : but they are of lb foft a nature, and fo ready to melt with a flight heat, that the colours laid on with them would
fully and be injured even by a gentle handling. On this account they require to be mixed with leed lac: and, to infpiflate the mixture diffidently to fufpend the colours, feme turpentine is alfo neceflary.
Maftic and fandarac muft be chofen for their whitenefs and tranfparency: and require xio other preparation for this ufe of them, than Co be well picked and powdered.
Of refm.
Refin is the caput mortuum -or refiduum left in the diftillation of turpentine for extraft- ixig the oil. It is of two kinds, white and thrown : the white is made when the turpen- cifit is diftilled with waterthe brown when rxo water is added to it. The white' turpentine Is ufed for rendering fpirit of wine a vehicle for colours in die fame manner as maftic or fan*« clarac; with which it agrees in its qualities, except that it is yet lefs hard and more liable to ftxily on handling : and the fame preparation *-r*d treatment is required for it as for them.
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