Part 194

At this stage the defects may be remedied by breaking off the faulty parts, patching them up, and then recoating the whole. With sign tablets there is no objection to doing so, but with hollow ware the fact remains that the article is faulty, no matter how carefully defects may be hidden. As white is the most general coating used, and shows up the defects more than the colored coatings, the greatest care is necessary at every stage of the manufacture. While glowing on the article, it should appear uniformly yellow, but on cooling it should revert to a pure white shade. On examining different makes of white coated articles, it will be found that some are more opaque than others. The former are less durable than the latter, because they contain a large percentage of oxide of tin, which reduces the elasticity. To ensure hardness the mixing must be very liquid, and this cannot be arrived at when a large quantity of oxide of tin is introduced.

Old utensils which have become broken or chipped can be repaired, although, except in the case of large articles, this is rarely done. The operations necessary are: (1) The defective parts chipped off; (2) submitted to a red heat for a few moments; (3) coated with gray on the exposed iron; (4) fused; (5) coated with the glaze on the gray; (6) fused.

«To Repair Enameled Signs.»—

Copal 5 parts Damar 5 parts Venice turpentine 4 parts

Powder the rosins, mix with the turpentine and add enough alcohol to form a thick liquid. To this add finely powdered zinc white in sufficient quantity to yield a plastic mass. Coloring {305} matter may, of course, be added if desired.

The mass after application is polished when it has become sufficiently hard.

«Enamel for Copper Cooking Vessels.»—White fluorspar is ground to a fine powder and strongly calcined with an equal volume of unburnt gypsum, at a light glowing heat, stirring diligently. Grind the mixture to a paste with water, paint the vessel with it, using a brush, or pour in the paste like a glaze and dry the same. Increase the heat gradually and bring the vessels with the glass substance quickly into strong heat, under a suitable covering or a mantle of burnt clay. The substance soon forms a white opaque enamel, which adheres firmly to the copper. It can stand pretty hard knocks without cracking, is adapted for cooking purposes and not attacked by acid matters. If the glassy substance is desired to cling well and firmly to the copper, a sudden and severe heat must be observed.

«To Pickle Black Iron-Plate Scrap Before Enameling.»—The black iron-plate scraps are first dipped clean in a mixture of about 1 part of sulphuric acid and 20 to 22 parts of water heated to 30° to 40° C. (86° to 104° F.), and sharp quartz sand is then used for scouring. They are then plunged for a few seconds in boiling water, taken out, and allowed to dry. Rinsing with cold water and allowing to dry thus may cause rust. The grains of quartz cut grooves in the fibers of the iron; this helps the grounding to adhere well. With many kinds of plate it is advisable to anneal after pickling, shutting off the air; by this means the plates will be thoroughly clean and free from oxidation. Much practice is required.—The Engineer.

«ENAMELED IRON RECIPES.»

The first thing is to produce a flux to fuse at a moderate heat, which, by flowing upon the plate, forms a uniform surface for the white or colored enamels to work upon.

Flux for Enameled Iron.—

White lead 10 parts Ball clay 1 part Flint glass 10 parts Whiting 1 part

The plates may then be coated with any of the following mixtures, which may either be spread on as a powder with a little gum, as in the case of the flux, or the colors may be mixed with oil and the plates dipped therein when coated; the plate requires heating sufficiently to run the enamels bright.

Soft Enamels for Iron, White.—

Flint glass 16 parts Oxide of tin 1 1⁠/⁠2 parts Niter 1 1⁠/⁠2 parts Red lead 4 parts Flint or china clay 1 part

Black.—

Red oxide of iron 1 1⁠/⁠4 parts Carbonate of cobalt 1 1⁠/⁠4 parts Red lead 6 parts Borax 2 parts Lynn sand 2 parts

Yellow Coral.—

Chromate of lead 1 part Red lead 2 3⁠/⁠4 parts Flint 1 part Borax 1⁠/⁠4 part

Canary.—

Oxide of uranium 1 part Red lead 4 1⁠/⁠2 parts Flint 1 1⁠/⁠2 parts Flint glass 1 part

Turquoise.—

Red lead 40 parts Flint glass 12 parts Borax 16 parts Flint 12 parts Enamel white 14 parts Oxide of copper 7 parts Oxide of cobalt 1⁠/⁠4 part

Red Brown.—

Calcined sulphate of iron 1 part Flux No. 8 (see page 307) 3 parts

Mazarine Blue.—

Oxide of cobalt 10 parts Paris white 9 parts Sulphate barytes 1 part

Fire the above at an intense heat and for use take