ETCHING VARNISHES. The var nishes of Mr. Lawrence, an English art ist resident in Paris, is made as follows : Take of virgin wax and asphaltum, each two ounces, of black pitch and burgundy pitch each half an ounce. Melt the wax and pitch in a new earthenware glazed pot, and add to them, by degrees, the as phaltum, finely powdered. Let the whole boil till such time as that, taking a drop upon a plate, it will break when it is cold, on bending it double two or three times betwixt the fingers. The varnish, being then enough boiled, must be taken off the fire, and after it cools a little, must be poured into warm water that it may work the more easily with the hands, so as to be formed into balls, which must be kneaded, and put into a piece of taf fety for use.
Care must be taken, first, that the fire be not too violent, for fear of burning the ingredients, a slight simmering being suf ficient; secondly, that whilst the asphal tum is putting in, and even after it is mixed with the ingredients, they should be stirred continually with the spatula ; and thirdly, that the water into which this composition is thrown should be nearly of the same degree of warmth with it, in order to prevent a kind of cracking that happens when the water is too cold.
The varnish ought always to be made harder in summer than in winter, and it will become so if it be suffered to boil longer, or if a greater proportion of the asphaltum or brown resin be used. The experiment above mentioned, of the drop suffered to cool, will determine the de gree of hardness or softness that may be suitable to the season when it is used.
Preparation of the hard varnish used by Callot, commonly called the Florence Varnish :—Take four ounces of fat oil very clear, and made of good linseed oil, like that used by painters ; heat it in a i clean pot of glazed earthenware, and af terwards put to it four ounces of mastiek well powdered, and stir the mixture briskly till the whole be well melted, then pass the mass through a piece of fine linen into a glass bottle with a long neck, that can be stopped very securely ; and keep it for the use that will be ex plained below.
Method of applying the soft varnish to the plate, and of blackening it :—The plate being well polished and burnished, as also cleansed from all greasiness by chalk or Spanish white, fix a hand-vice ou the edge of the plate where no work is intended to be, to serve as a handle for managing it when warm ; then put it upon a chafing-dish, in which there is a moderate fire, and cover the whole plate equally with a thin coat of varnish ; and whilst the plate is warm, and the varnish upon it in a fluid state, beat every part of the varnish gently with a small ball or dauber made of cotton tied up in tatlety, which operation smooths and distributes the varnish equally over the plate.