All processes of steel etching depend on the coating of the steel with a resist, which is scraped away from those portions to be etched or bitten into by chemical action. The resist or etching ground is made by melting together over a slow fire black pitch, white wax, Burgundy pitch, asphaltum, and gum mastic. Other etching grounds are (1) asphaltum varnish; (2) yellow beeswax dissolved in turpentine and continuously decanted until no sediment remains - to 6 parts of this add 1 part of japan varnish; (3) asphaltum, Burgundy pitch, and beeswax melted together. The resist may either be melted and then brushed on, or the steel maybe warmed so that on rubbing it with the resist the latter will melt and leave a thin film. The resist is allowed to become cold and hard, and is then drawn on with needles or, preferably, with a stick of steel of i-in. diameter round or square section tapering to a fine point at each end; the weight of this tool is sufficient to penetrate and remove the resist as it is drawn along, thus leaving the hand more at liberty to draw freely or form letters as the case may be. If the steel is in the form of a plate, it now has a wall of wax built around its edges, and into the shallow dish thus formed the etching acid is poured.
Knife blades and similar small articles having been properly coated with resist, may be dipped into the acid, or the latter may be applied to the portions to be etched by means of a camel-hair pencil or a stick, at the end of which is mounted a little ball of tissue-paper. Remember that all portions not covered with the resist will be etched. The etchingacid may be any of the following mixtures. (1) Pyroligneous acid, nitric acid, and water; (2) diluted nitrous acid; (3) 2oz. of copper sulphate, 1/2oz. of alum, 1/2 oz. of salt, 1/2 pt. of vinegar, and 10 drops of nitric acid; (4) 1 parts of glacial acetic acid and 1 part of absolute alcohol; allow to remain for thirty minutes, and add gradually 1 part of nitric acid; (5) 1 part of fuming hydrochloric acid and 7 parts of water: add boiling solution of potassium chlorate and dilute with water. When the acid has bitten sufficiently deep, pour it off or remove it, and wash thoroughly in clean water. If it is required to etch more deeply certain portions, cover up the rest with a stopping ground of lampblack and Venice turpentine, or with any of the above etching grounds, and apply the acid again.
When the etching is complete, wash off all traces of acid.
To write names, etc., on steel cover the surface to be marked with a thin layer of asphaltum varnish, making a little bank at the edges. On the varnish write the names, etc., with a steel scriber, and, in the small basin formed by the asphalt banks, pour a weak solution of nitric acid. When this has eaten in to the required depth, wash With hot water, removing the varnish with hot turpentine. Instead of asphalt varnish, soft beeswax is often used, and an etching fluid may be made from iodine 1 oz., iron filings 1/2 dram, and water about 4 oz. A solution of iodine, potassium iodide, and water is sometimes used; also a solution of 1 part of nitric acid (by measure),1 of hydrochloric acid, and 10 of water.