Coating Castings with Gold and Silver.

Scientific American 15, 9.10.1869

Gilding. - Gilding cast iron by means of gold amalgam is very difficult, as the amalgam does not stick to the iron. It is therefore necessary to brush the well-cleaned surface of the iron with a concentrated solution of copper vitriol, and to apply the amalgam to the precipitated copper. As under certain circumstances the coating of copper is injurious, Böttger coats the articles direct with mercury by means of the electropositive zinc in the following manner: The article to be gilded is well cleaned and boiled in a porcelain vessel together with 12 parts of mercury, 1 part of zinc, 2 parts of iron vitriol, 1½ parts of muriatic acid of 1.2 specific gravity, and 12 parts of water; in a short time a lyer of mercury will deposit upon the iron, and upon this the gold amalgam may be uniformly distributed.

The gilding may also be effected upon polished iron in the following manner: If a nearly neutral solution of chloride of gold be mixed up with wulphuric ether and agitated, the ether will take up the gold and float above the denser liquid. When this auriferous ether is applied by a camel gair pencil to brightly polished iron or steel, the other evaporates and the gold adheres. it is fixed by polishing with a burnisher. This gilding is not very rich or durable; in fact the affinity between gold and iron is feeble compaerd to that between gold and copper or silver.

Gilding of cast iron by the galvanic way is also difficult, and is successful only if the article is perfectly clean. It is advisable previously to coat the article with copper or silver.

Gilding of cast iron by the galvanic way is also difficult, and is successful only if the article is perfectly clean. It is advisable previously to coat the article with copper or silver.

Polished iron may also be gilded with heat by gold leaf.

Silvering Cast Iron. - Iron to be silvered is first provided with a coating of copper, upon which the silver is applied either by means of amalgam or silver leaf.

Cast iron can be well silvered by the galvanic way without a previous coppering.

- Practical Treatise on Metallurgy. -