The japanners' oven is a receptacle in which the work is placed when being heated. Usually the heat is applied by means of external flues in which hot air or steam is circulated. By this system the temperature may be regulated to great nicety, the supply of heat being controlled by dampers or stop-cocks. A sheet iron box, encased by another of the same shape, but somewhat larger in size, so that an interspace of an inch or two exists between them, is the most simple form of oven. Heat is applied to the interspace, and thus an even temperature is maintained. A flue must be provided to carry off the vapours which arise from the japan. A doorway, by which to introduce the articles, provided with a tolerably well-fitting door, is, of course, essential. Hooks or wire shelves are provided, by which the work is supported, so that the heat may take effect equally all round. Moisture, dust, and all other extraneous matter must be carefully excluded, so that the japanning may be kept perfectly clean and free from foreign substances.
Thermometers are hung in the oven to indicate the precise degree of heat, which is regulated as explained above, to suit the requirements of particular work.
Metals require no special preparation before laying on the japan. After being wrought to the desired shape, and smoothed as much as may be considered advisable, the article has only to be made thoroughly clean to prepare it for japanning. The surface must be quite dry, or the japan will not adhere properly. Wood requires to be primed and otherwise prepared for japanning.
Japan, that is the paint-like material to be laid on the metal, is made of shellac varnish, with which may be incorporated any pigment necessary to produce a desired colour. Shellac varnish is made by dissolving shellac in alcohol. A better varnish for japanning is made by adding resin and shellac, 2oz. of each, to 1 pint methylated spirit. Any pigment may be added to such varnish to form japan of the colour required. A few formulae may be useful. Black: Mix lampblack or ivory-black - this latter preferably - with the above varnish. Another black: Melt lib. asphaltum, and mix with the same quantity of balsam of capivi, thin the mixture to a workable consistency with hot oil of turpentine. Another black: Mix lampblack with oil of turpentine, and grind smooth on a rauller, thin the mixture with copal varnish. White: Flake white, or white lead, ground up with 1/6 of its weight of starch; this must be thoroughly dried, and mixed with mastic varnish. Yellow: King's yellow is used as the pigment, but the effect is considerably improved by dissolving turmeric in the alcohol before adding the shellac to form the varnish.
Various colours are made simply by the incorporation of a suitable pigment in the varnish made as described above.
Tortoiseshell japan is extremely pretty, and comparatively easy to manipulate. The work is first coated with a japan made by boiling 2 pints linseed oil, to which 1/4 lb. umber has been added, till it becomes thickened; the mixture is then strained and further boiled till it becomes of a pitchy consistency. This is mixed with turpentine to a workable consistency and then applied. On a thoroughly dry coating of this japan lay a quantity of vermilion spots to represent the clear portions of the shell. The vermilion japan is made by adding vermilion to shellac varnish; it should be laid on thinly and dried. The whole surface is then finally coated with a thin layer of the above described brown japan, still further diluted with turpentine. A long course of stoving will be necessary to thoroughly harden the japanning.
The operation of japanning consists of driving off the solvents of the japan at a high temperature. When the article, covered with a coating of japan, is placed in the oven and submitted to a temperature of about 300 F. and even more, the solvents quickly evaporate. - The residue, a gummy substance, with which is incorporated the colouring matter, is kept liquid by the heat, and in the semi-liquid state forms a smooth coating filling any small inequalities of the surface. The baking process secures a very firm adhesion of the japan to the metal, far superior to that of ordinary varnish or paint. The japan is also made hard, and consequently better able to resist wear. When one coat is dried another is applied and sub-mitted to the action of heat. These operations are repeated, as may be deemed necessary, from one to six times. Each succeeding coat of japan will present a more uniform and glassy surface. The natural flow of the japan generally suffices to produce a good smooth surface, but in some cases a processof polishing is resorted to before the application of the final coat.
The temperature for light-coloured japans must not be sufficiently high to scorch, or the surface will, of course, be discoloured. Dark japans are usually dried at a very high temperature, if the article is not likely to be injured by heat. The final coating of japan is generally a layer of clear varnish, which will add to the lustre of the surface. Practical experience is the best, and, indeed, the only guide by which proficiency in the art of japanning can be attained. (P. N. Hasluck.) (A) Wood. - A lacquer of great elasticity, perfectly supple and not liable to peel off, is made in the following manner: - About 120 lb. oil varnish is heated in one vessel, and 33 lb. quicklime is put into 22 lb. water in another. As soon as the lime causes an effervescence, 55 lb. melted rubber are added. This mixture is stirred, and then poured into the vessel of hot varnish. The whole is then stirred so as to be thoroughly mixed, then strained and allowed to cool, when it has the appearance of lead. When required for use, it is thinned with the necessary quantity of varnish, and applied with a brush, hot or cold - preferably the former.
(0 White is the usual type for Tonbridge ware, etc. Therefore the grain should be filled up with plastter of Paris and glue size. As a matter of course the wood should be white, such as pine, chestnut, lime, or holly. After filling up the grain, well paper the surface, smooth with glass paper; no oil must be used on any account. If the appearance is not satisfactory when papered down, give another coat of glue, size, and plaster of Paris, paper down smooth, then give the article a coat of varnish made as follows: - 1/2 lb. flake white, 1/2 gill spirits of turpentine, 1/2 gill spirit varnish, such as white hard varnish or glaze. (N.B. - It must be borne in mind, as the quality of flake white and the thickness of the varnish vary, the quantity must not be taken as quite exact, but the amateur must be guided by circumstances.) When the first coat is dry, paper down and give another coat; paper down again, give another coat. When quite set give the whole piece of work a coat of white hard varnish, or, if preferable, a coat of glaze. Work done in this style will last for years. Should it at any time get bruised, it may be papered down and revarnished.
In grinding colours for coloured work, great care should be taken that the mixture is worked quite smooth, using spirits of turpentine only. Never mix with varnish until the colour has been well mixed with turps, and never mix a greater quantity than will be used at any one time. For colour japanning the following colours are used: - Flake white, red lead, vermilion, Prussian blue, chrome yellow, the various ochres, Vandyke brown, umber, lamp*. black, blue black, drop black. With these any colour may be matched. For black japan a simple plan is to stain . the article, or even paint it with lamp black and turps. After the grain is filled up, then varnish it with black japan thinned with turps, after which give the article a coat of white hard varnish, darkened with ivory black, or it may be finished off with a mixture of gold size and ivory black, but must have two coats.
Well cleanse the covers from grease by washing in sulphuric acid and water. Rinse in cold water until quite free from acid. Purchase any quantity, say 1 pint, black, brown, yellow, or red japan varnish; pour a small quantity of varnish in a cup. Place the cover in a warm oven until quite hot; remove from the oven, varnish the cover in one direction, using a camel hair brush. When every part required to be varnished is done, place the cover in the oven for 2 or 3 hours. If the article to be varnished is too large for the oven, it should be made quite hot in front of the fire, and same after varnishing, but care must be taken not to allow it to blister, and to keep free from dust and draughts of cold air.