1. 2 oz. india-rubber, finely divided, placed in a phial, and digested in a sand bath, with 1/4 lb. of camphene, and 1/4 oz. of naphtha. When dissolved add 1 oz. of copal varnish, which renders it more durable. 2. Digest in a wide-mouthed glass bottle 2 oz. of india-rubber in shavings, with 1 lb. of oil of turpentine, during two days, without shaking, then stir up with a wooden spatula. Add another lb. of oil of turpentine, and digest, with frequent agitation, until all is dissolved. Mix 1 1/2 lb. of this solution with 2 lbs. of white copal-oil varnish, and 1 1/2 lb. of boiled linseed oil; shake and digest in a sand bath until they have united into a good varnish. 3. 4 oz. india-rubber in fine shavings dissolved in a covered jar by means of a sand bath, in 2 lbs. of crude benzole, and then mixed with 4 lbs. of hot linseed-oil varnish and 1/2 lb.of oil of turpentine. Dries well.
Take india-rubber and dissolve it in 5 times its weight of spirits of turpentine, keeping them some time together, then boil gently 1 part of this solution with 8 parts of boiled linseed oil for a few minutes, strain and set aside to cool. It must be applied warm.
All varnish brushes ought to be made of long white hairs of the best quality, and, for the general purposes of varnishing, have a good regular spring, with about one-fourth or fifth part worn off, flat, sharp, and thin at the point, so as to lay on the varnish smoothly and regularly. As the beauty of varnishing depends in a great measure on the brush as well as the manner of laying it on, great care is also necessary that no oil brush be put into varnish; therefore, all brushes worn down in oil colour, and intended to be put into varnish, ought previously to be well washed in turpentine, squeezed and dried with a clean linen rag, or well washed with soap and hot water, rinsed in clean warm water, and made perfectly dry. The best method of keeping oil-varnish brushes when not in use, is to bore a hole through the handle and put a wire skewer through it, and so suspend the brush, in a narrow tin pot containing varnish of the same sort as it was last in, taking care that the varnish in the pot covers the hairs of the brush up to the binding and no higher.
Brushes so kept are always straight, clean, pliable, and in good order; whereas varnish brushes kept in turpentine become hard and harsh, and however well stroked or rubbed out, there will still remain turpentine enough to work out by degree*) and spoil the varnishing, by causing it to run streaky or cloudy.
Grind a small quantity of Chinese blue and chromate of potash together, and mix them thoroughly in common copal varnish thinned with turpentine. The blue and the chromate must be ground to an impalpable powder, and the tone of colour varied with the amount of each ingredient used. A yellow-green requires about twice the quantity of the chromate of potash to that of the Chinese blue.
Pulverize 1 drachm of saffron and 1/2 drachm of dragon's blood, and put them into 1 pint spirits of wine. Add 2 oz. of gum shellac and 2 drachms of socotrine aloes. Dissolve the whole by gentle heat. Yellow painted work varnished with this mixture will appear almost equal to gold.
In purchasing gum, examine it, and see that it consists, for the most part, of clear transparent lumps, without a mixture of dirt; select the clearest and lightest pieces for the most particular kinds of varnish, reserving the others, when separated from extraneous matter, for the coarser varnishes. In choosing spirits of wine, the most simple test is to pour a small quantity into a cup, set it on fire, and dip a finger into the blazing liquid; if it burns quickly out, without burning the finger, it is good; but if it is long in burning, and leaves any damp-ness remaining on the finger, it is mixed with inferior spirit; it may be also compared with other spirit, by comparing the weight of equal quantities, the lightest is the best. The goodness of spirits of turpentine may be likewise ascertained by weighing it, and by noticing the degree of inflammability it possesses; the most inflammable is the best; and a person much in the habit of using it will tell by the smell its good or bad qualities; for good turpentine has a pungent smell, the bad a very disagreeable one, and not so powerful.
Pale shellac, 5 oz.; borax, 1 oz.; water, 1 pint. Digest at nearly the boiling point till dissolved, then strain. An excellent vehicle for water colours, inks, etc, and a varnish for prints is madethus of bleached lac. When dry, it is transparent and. waterproof.