Here is a recipe for a,jet-black marking ink. Dissolve 1 dr. of silver nitrate in a little water, slowly add ammonia until the oxide which first precipitates is redissolved, mix with a little indigo extract or sap green, and add strong gum water to make 1 oz. Write with a quill pen, and afterwards run a hot iron over the writing. For an indelible ink to be applied with a stencil, dissolve asphaltum in coal-tar naphtha or turpentine to form a syrupy solution. Apply with a stiff stencil brush. The following is a very fine indelible marking ink. Add caustic alkali to a saturated solution of cuprous chloride until no further precipitate forms; allow to settle, draw off the liquid, and dissolve the oxide in the smallest quantity of ammonia that will absorb it. Mix with about 6 per cent. of gum dextrine.