Marking steel tools is sometimes done by an etching process, carried out as follows: A rubber stamp making white letters on a black ground is required. Then an ink to use with this stamp is made with resin, 1/2 lb.; lard oil, 1 tablespoonful; lampblack, 2 tablespoonfuls; turpentine, 2 tablespoonfuls. Melt the resin and stir in the other ingredients in the order given. When the ink is cold it should be like the ordinary printer's ink. Spread a little of the ink over the pad, ink the rubber stamp as usual, and press it on the clean steel - on a saw blade, for instance. With a strip of soft putty make a border round the stamped design as close up to the lettering as possible, so that no portion of the steel inside the ring of putty is exposed except the lettering. Pour the etching mixture into the putty ring composed of 1 oz. of nitric acid, 1 oz. of muriatic acid, and 12 oz. of water. Allow it to rest for only a minute, draw off the acid with a glass or rubber syringe and soak up the last trace of acid with a moist sponge. Take off the putty and wipe off the design with potash solution first, and then with turpentine.