Part 242

«Simple Specific Gravity Test.»—A certain quantity of the metal is taken and drawn out into a wire, which is to be exactly of the same length as one from fine silver; of course, both must have been drawn through the same hole, silver being nearly 1⁠/⁠2 lighter than gold, it is natural that the one of fine silver must be lighter, and the increased weight of the wire under test corresponds to the percentage of gold contained in it.

«To Make Fat Oil Gold Size.»—First thin up the fat oil with turpentine to workable condition; then mix a little very finely ground pigment with the gold size, about as much as in a thin priming coat. Make the size as nearly gold color as is convenient; chrome yellow tinted with vermilion is as good as anything for this purpose. Then thin ready for the brush with turpentine, and it will next be in order to run the size through a very fine strainer. Add japan, as experience or experiment may teach, to make it dry tacky about the time the leaf is to be laid. Dry slowly, because the slower the size dries, the longer it will hold its proper tackiness when it is once in that condition.

«To Dissolve Copper from Gold Articles.»—Take 2 ounces of proto-sulphate of iron and dissolve it in 1⁠/⁠2 a pint of water, then add to it in powder 2 ounces of nitrate of potash; boil the mixture for some time, and afterwards pour it into a shallow vessel to cool and crystallize; then to every part of the crystallized salt add 8 ounces of muriatic acid, and preserve in a bottle for use. Equal parts of the above preparation and of boiling water is a good proportion to use in dissolving copper, or 1 part by weight {383} of nitric acid may be used to 4 parts by weight of boiling water as a substitute.

«GOLD PURPLE.»

I.—The solution of stannous chloride necessary for the preparation of gold purple is produced by dissolving pure tin in pure hydrochloric acid (free from iron), in such a manner that some of the tin remains undissolved, and evaporating the solution, into which a piece of tin is laid, to crystallization.

II.—Recipe for Pale Purple.—Dissolve 2 parts by weight of tin in boiling aqua regia, evaporate the solution at a moderate heat until it becomes solid, dissolve in distilled water and add 2 parts by weight of a solution of stannous chloride (specific gravity 1.7) dilute with 9,856 parts by weight of water, stir into the liquid a solution of gold chloride prepared from 0.5 parts by weight of gold and containing no excess of acid (the latter being brought about by evaporating the solution of gold chloride to dryness and heating for some time to about 320° F.). This liquid is dimmed by the admixture of 50 parts by weight of liquid ammonia which eliminates the purple. The latter is quickly filtered off, washed out and while still moist rubbed up with the glass paste. This consists of enamel of lead 20 parts by weight; quartzose sand, 1 part by weight; red lead, 2 parts by weight; and calcined borax, 1 part by weight, with silver carbonate, 3 parts by weight.

III.—Recipe for Dark Gold Purple.—Gold solution of 0.5 parts by weight of gold, solution of stannous chloride (specific gravity 1.7) 7.5 parts by weight; thin with 9,856 parts by weight of water, separate the purple by a few drops of sulphuric acid, wash out the purple and mix same with enamel of lead 10 parts by weight and silver carbonate, 0.5 parts by weight.

IV.—Recipe for Pink Purple.—Gold solution of 1 part by weight of gold; solution of 50 parts by weight of alum in 19,712 parts by weight of water; add 1.5 parts by weight of stannous chloride solution (specific gravity 1.7) and enough ammonia until no more precipitate is formed; mix the washed out precipitate, while still moist, with 70 parts by weight of enamel of lead and 2.5 parts by weight of silver carbonate. According to the composition of the purple various reds are obtained in fusing it on; the latter may still be brightened up by a suitable increase of the flux.

«To Render Pale Gold Darker.»—Take verdigris, 50 parts by weight and very strong vinegar, 100 parts by weight. Dissolve the verdigris in the vinegar, rub the pieces with it well, heat them and dip them in liquid ammonia diluted with water. Repeat the operation if the desired shade does not appear the first time. Rinse with clean water and dry.

«To Color Gold.»—Gilt objects are improved by boiling in the following solution: Saltpeter, 2 parts by weight; cooking salt, 1 part by weight; alum, 1 part by weight; water, 24 parts by weight; hydrochloric acid, 1 part by weight (1.12 specific gravity). In order to impart a rich appearance to gilt articles, the following paste is applied: Alum, 3 parts by weight; saltpeter, 2 parts by weight; zinc vitriol, 1 part by weight; cooking salt, 1 part by weight; made into a paste with water. Next, heat until black, on a hot iron plate, wash with water, scratch with vinegar and dry after washing.

«Gold-Leaf Striping.»—To secure a good job of gilding depends largely for its beauty upon the sizing. Take tube chrome yellow ground in oil, thin with wearing body varnish, and temper it ready for use with turpentine. Apply in the evening with an ox-tail striper, and let it stand until the next morning, when, under ordinary circumstances, it will be ready for the gold leaf, etc. After the gilding is done, let the job stand 24 hours before varnishing.

«Composition of Aqua Fortis for the Touch-Stone.»—Following are the three compositions mostly in use: I.—Nitric acid, 30 parts; hydrochloric acid, 3 parts; distilled water, 20 parts.

II.—Nitric acid, 980 parts by weight; hydrochloric acid, 20 parts by weight.

III.—Nitric acid, 123 parts by weight; hydrochloric acid, 2 parts by weight.

«To Remove Soft Solder from Gold.»—Place the work in spirits of salts (hydrochloric acid) or remove as much as possible with the scraper, using a gentle heat to remove the solder more easily.

«Tipping Gold Pens.»—Gold pens are usually tipped with iridium. This is done by soldering very small pieces to the points and filing to the proper shape.

«To Recognize Whether an Article is Gilt.»—Simply touch the object with a glass rod previously dipped into a solution of bichloride of copper. If the article has been gilt the spot touched should remain intact, while it presents a {384} brown stain if no gold has been deposited on its surface.

«To Burnish Gilt Work.»—Ale has proved a very good substitute for soap and water in burnishing gilt as it increases the ease and smoothness with which it is accomplished. Vinegar is a somewhat poorer substitute for ale.

«White-Gold Plates Without Solder.»—The gold serving as a background for white-gold is rolled in the desired dimensions and then made perfectly even under a powerful press. It is then carefully treated with a file until a perfectly smooth surface is obtained. After a white-gold plate of the required thickness has been produced in the same manner, the surfaces of the two plates to be united are coated with borax and then pressed together by machine, which causes the harder metal to be squeezed slightly into the surface of the other, furnishing a more solid and compact mass. The metals, now partially united, are firmly fastened together by means of strong iron wire and a little more borax solution is put on the edges. Then heat to the temperature necessary for a complete adhesion, but the heat must not be so great as to cause an alloyage by fusing. The whole is finally rolled out into the required thickness.

«To Fuse Gold Dust.»—Use such a crucible as is generally used for melting brass; heat very hot; then add the gold dust mixed with powdered borax; after some time a scum or slag will be on top, which may be thickened by the addition of a little lime or bone ash. If the dust contains any of the more oxidizable metals, add a little niter, and skim off the slag or scum very carefully; when melted, grasp the crucible with strong iron tongs, and pour off immediately into molds, slightly greased. The slag and crucibles may be afterwards pulverized, and the auriferous matter recovered from the mass through cupellation by means of lead.

GOLD ALLOYS: See Alloys.

GOLD, EXTRACTION OF, BY AMALGAMATION: See Amalgams.

GOLD LETTERS ON GLASS, CEMENTS FOR AFFIXING: See Adhesives, under Sign-Letter Cements.

GOLD, REDUCTION OF OLD PHOTOGRAPHIC: See Photography.

GOLD FOIL SUBSTITUTES AND GOLD LEAF: See Metal Foil.

GOLD-LEAF ALLOYS: See Alloys.

GOLD LEAF AND ITS APPLICATION: See Paints.

GOLD PLATING: See Plating.