That which is used for mixing varnish ought to be procured and chosen as pure, strong and free from acid as possible. Some turpentine being drawn from green trees abounds with a pyroligenous acid, which rises and comes over with the spirit in distillation; it is strong and bitter to the taste, and appears milky, particularly towards the bottom, after standing to settle. Therefore, the longer turpentine is kept before it is used, the purer it will be.
Fuse 8 lbs. of very clean pale African gum copal, and when completely fluid, pour in 2 gallons of hot oil; let it boil until it will string very strong; and in about fifteen minutes, or while it is yet very hot„pour in 3 gallons of turpentine. Perhaps, during the mixing, a considerable quantity of the turpentine will escape, but the varnish will be so much the brighter, transparent, and fluid; and will work freer, dry quickly, and be very solid and durable when dry. After the varnish has been strained, if it is found too thick, before it is quite cold, heat as much turpentine and mix with it as will bring it to a proper consistence.
From a select parcel of scraped African gum copal, pick out the fine transparent pieces which appear round and pale like drops of crystal; break these small; dry them in the sun, or by a very gentle fire. Afterwards, when cool, bruise or pound them into a coarse powder; then procure some broken bottles or flint glass, and boil the same in soft water and soda, then bruise it into coarse powder like the gum; boil it a second time, and strain the water from it, washing it with three or four waters, that it may be perfectly clean and free from grease or any impurity; dry it before the fire, or upon a plate; set it in an oven. When it is thoroughly dry, mix 2 lbs. of it with 3 lbs. of the powdered copal; after mixing them well, put them into the gum pot and fuse the gum; keep stirring all the time; the glass will prevent the gum from adhering together, so that a very moderate fire will cause the gum to fuse. When it appears sufficiently run, have ready 3 quarts of clarified oil, very hot, to pour in.
Afterwards let it boil until it strings freely between the fingers; begin and mix it rather hotter than if it were body-varnish; pour in 5 quarts of old turpentine, strain it immediately, and pour it into an open jar or large glass bottle; expose it to the air and light, but keep it both from the sun and wet, and from moisture, until it is of a sufficient age for use. This is the finest copal varnish for fine paintings or pictures.
Fuse 7 lbs. of fine African gum copal, and pour in half a gallon of clarified oil; in three or four minutes after, if it feels stringy, take it out of doors, and mix with it 3 gallons of turpentine; afterwards strain, it, and put it aside for use. This, if properly boiled, will dry in ten minutes, but if too strongly boiled will not mix at all with the turpentine; and sometimes, when boiled with the turpentine, will mix, and yet refuse to amalgamate with any other varnish less boiled than itself; therefore it requires a nicety which is only to be learned from practice. This varnish is chiefly intended for the use of japanners, cabinet painters, and coach painters.
Fuse 8 lbs. of fine African gum copal; add 2 gallons of clarified oil; boil very slowly for four or five hours, until quite stringy; mix off with 3 1/2 gallons of turpentine; strain off, and pour it into a cistern.
8 lbs. of fine pale gum anime, 2 gallons of clarified oil, 3 1/2 gallons of tur-pertine; to be boiled tour hours. This, after being strained, is put into the two former pots, and well mixed together; its effect is to cause the whole to dry quicker and firmer, and enable it to take the polish much sooner.
8 lbs. of the best African copal, 3 gallons of clarified oil, 3 1/2 gallons of turpentine; boiled four hours, or until stringy; mixed and strained, will produce about 5 1/2 gallons. 8 lbs. of the best gum anime, 2 gallons of clarified oil, 3 1/2 gallons of turpentine; boiled as usual; mixed and strained hot, and put into the former pot of African gum varnish. Put two pots of this anime varnish to one of copal; it will dry quicker and harder than the best body copal, and will polish very soon, but not wear either so well or so long.
8 lbs. of the best African copal, 2 gallons of clarified oil, 1/4 lb. of dried sugar of lead, 3 1/2 gallons of turpentine; boiled till stringy, and mixed and strained; 8 lbs. of fine gum anime, 2 gallons of clarified oil, J lb. of white copperas, 3 1/2 gallons of turpentine; boiled as before; to be mixed, and strained while hot, into the other pot. These two pots mixed together will dry in six hours in winter, and in four in summer; it is very useful for Tarnishing old work on dark colours.
8 lbs. of 2nd sorted African copal, 2 1/2 gallons of clarified oil; boil till very stringy. 1/4 lb. of dried copperas, 1/4 lb. of litharge, 5 1/2 gallons of turpentine; strained. 8 lbs. of 2nd sorted gum anime, 2 1/2 gallons of clarified oil, 1/4 lb. of dried sugar of lead, 1/4 lb. of litharge, 5 1/2 gallons of turpentine; mix with the first while hot. This varnish will dry hard, if well boiled, in four hours in summer, and six in winter. As its name denotes, this is intended for the varnishing of the wheels, springs, and carriage parts of coaches, chaises and so on; also it is that description of varnish which is generally sold to and used by house painters and decorators, as from its drying quality and strong gloss it suits their general purposes well.
8 lbs. of 2nd sorted gum anime, 2 3/4 gallons of fine clarified oil, 5 1/4 gallons of turpentine, 1/4 lb. of litharge, 1/4 lb. of dried sugar of lead, 1/4 lb. of dried copperas; boiled and mixed as before. When three runs are poured into the boiling pot, the regular proportion of driers put in, and well boiled, this varnish will dry hard and firm in four hours in winter, and in two in summer: it is principally intended for varnishing dark carriage-work or black japan, and is also used by house painters for dark work.