Varnish for out-door Painting. Boil half agallon of linseed oil in an iron pot, for an hour, and then lay in it a round of cram of bread, to absorb the fat, and boil some time. Take out the bread, and put in a lb. of powdered rosin gradually, and stir with an iron spatula. Add 4 oz., or more, of the spirits of turpentine, and strain it. It bears weather, wear, and hot water. The same may also be made of 1 oil of turpentine and 4 rosin, well boi'ed. Or, by boiling 16 drying linseed oil, 8 of gum sandarac, and 1 of oil of turpentine.
It is usual, in the manufacture of spirit varnishes, to mix glass or sand with the resin, for the purpose of affording ready access of the alcohol to all parts of the solid mass. M. Ferrari, however, recom mends that, in place of these substances, coarsely powdered charcoal should be used ; for the glass or sand frequently tends to aggregate the resin at the bottom of the vessels and protect it from the solvents, whilst, on the contrary, the charcoal rather tends to raise and divide it. The most advantageous proportion appears to be about 1 oz. of charcoal to 1 lb. of the spirits or the oil of turpentine.
To Varnish Silk. If the surface of the silk be pretty large, it is made fast in a wooden frame furnished with hooks and movable pegs. A certain quantity of a soft paste, composed of linseed-oil, boil ed with a fourth part of litharge, white of Troyes, Spanish white or tobacco-pipe clay, lamp-black and litharge, is then prepared, in nearly the following propor tions : tobacco-pipe clay, dried and sifted through a silk sieve, 16 parts ; litharge, ground with water, dried and sifted in the same manner, 8 parts ; lamp-black, 1 part. This paste is then spread in an
uniform manner over the surface of the silk, by means of a long knife, having a handle at each extremity.
In summer, 24 hours are sufficient for drying, and when dry, the knots produ ced by the inequalities of the silk are smoothed with pumice-stone. This ope ration is performed with water ; and, when finished, the surface of the silk is washed. It is then suffered to dry, and copal varnish applied.
If it be intended to polish this varnish, it will be proper to apply a second stra tum; after which it is polished with a ball of cloth and very fine tripoli, or with a piece of strong cloth only. The var nished silk which results from this pro ces is very black, exceedingly pliable, and has a fine polish. It may be rumpled any way without retaining any fold, or the mark of a fold.
Varnished silk, which has a yellowish color, is prepared with a plain varnish. The silk is covered with a mixture of three parts of boiled oil of poppy, and one part of fat copal varnish, which is spread with is coarse brush, or with a knife. Two coats are sufficient, when the oil has been freed from its greasy principles over a slow fire, or when it has been boiled with a fourth part of its weight of litharge.
White Varnish. In 1 quart of alcohol mix 1 lb. of juniper gum and 6 oz. of Strasburgh turpentine. For wood, linen, and paper.
'Rite Hard Varnish. Pulverize 8 oz. of cutlet (flint glass, or use 3 oz. of pot ter's dried flint); mix with 4 oz. of mastic, and 2 oz. of juniper gum and of Venice turpentine, which put into 1 quart of alcohol. For cards, sheaths, &c.