The only really reliable marking inks that will not wash out of linen, apart from stamping inks, are those that contain compounds of silver, gold, or platinum. Silver inks are indelible as long as the fabric lasts, but they become paler as the fabric wears away. Chloride of lime or eau-de-javelle bleaches silver marking ink, the action being to convert the black metallic silver into white silver chloride. The following recipes are for silver inks: - (a) Nitrate of silver 17 parts, ammonia 42 parts, carbonate of soda 22 parts, gum 20 parts, sulphate of copper 33 parts, distilled water 85 parts. Dissolve the carbonate of soda in 25 parts of water, the gum in 50 parts of water, and the nitrate of silver in 10 parts of water. To the solution of nitrate of silver add the ammonia and shake thoroughly; mix the solutions of gum and carbonate of soda and add to the silver solution; finally add the sulphate of copper and shake till dissolved. (d) Dissolve 2 dr. of nitrate of silver in l 1/2 oz. of water and add strong ammonia gradually until the precipitate which fl st forms is just re-dissolved, make up to 2 oz. with water, and colour with a little indigo extract, sap green, or any suitable aniline colour.

It is usual to press a hot iron upon the marking so that the ink may decompose and the silver be reduced.