Photo-engraving, Photo-etching and Photo-lithography in Line and Half-tone / Also Collotype and Heliotype

by W. T. Wilkinson

Acid Mordants.—(Lalanne.)
Nitric Acid, at 40°	1	part.
Water	1	part.

With a little old etching solution added, or pieces of scrap copper.

Malaret.
Nitric or Sulphuric Acid	1	part.
Saturated Solution of Bichromate of Potash	2	parts.
Water	5	parts.

Fizeau used for daguerrotype etching a mordant composed of nitric, nitrous, and hydrochloric acids.

Dutch Mordant.
	Fuming Muriatic Acid (specific gravity, 1.190)	10	parts.
	Water	70	parts.
To this add a boiling solution of
	Chlorate of Potash	2	parts.
	Water	20	parts.

This may be diluted with from 100 to 400 parts of water as required.

Perchloride of iron, more or less diluted in water, is, according to Hamerton, an excellent mordant. It bites deep and clear, without enlarging the line much, and there is no ebullition, as with nitric acid. It is particularly useful in photographic etching through gelatine, as the latter is insoluble in it.

In most cases the mordant is flowed over the plate, or kept moving on it in the same way as a photographic developer. Such mordants are generally used for finishing off and deepening the light tints, and are called eau fortis à couler or à passer. The following formulæ are given: {113}

Roret.—(Abraham Rosse’s.)
Strong White or Distilled Vinegar	3	litres.
Sal Ammoniac	180	grammes.
Common Salt	180	grammes.
Pure Verdigris	120	grammes.

A little oxalic acid is sometimes added. The solids are ground up, and boiled in the vinegar. Acetic acid at 3°, or pyroligneous acid, may be used in place of vinegar, and, if too strong, more vinegar should be added.