Many objects may well be left with a plain polished surface. In some cases, however, you may wish to apply a monogram, a decorative design, or otherwise modify the smooth finish of the metal.
Planishing is one of the commonest methods of finishing metal. This consists of giving it an uneven surface by hammering it with the round end of a ball pein hammer (fig. 101). The article should rest on a metal surface, an anvil for flat work, a rounded metal stake for curved objects. Generally it is best to start at the middle and to work in a roughly circular fashion, letting the dimples caused by the hammering overlap each other to some extent. Planishing hardens the metal greatly and adds to its durability.
Fluting is also a hammered form of decoration. It is applied chiefly to rims and edges. A wooden stake must be shaped to fit the rim of the bowl or tray. A groove is filed in the head of the stake to the shape of the flute desired. It may be of uniform width and depth, or it may taper at one end. The article is held over the stake and the metal hammered down into the groove with the narrow end of a wedge-shaped hammer (fig. 102).
Designs and monograms may be applied by chasing or etching. In chasing, the design is incised on the surface with special tools. They may be purchased or filed from strips of tool steel or discarded files. They may even be made from spikes if they are to be used on the softer metals. A few common designs are illustrated, but you can also make up patterns of your own (fig. 103).
(1) Chasing should be done on flat metal if possible. If a bracelet or small object is to be chased, it is best to do it before the article is formed. Place the metal on a fairly soft surface such as a piece of linoleum. Hold the chasing tool perpendicular to the metal and strike it lightly but squarely with the flat face of the ball pein hammer (fig. 104). You may chase either the design itself or the background around it. Metal may also be pierced and cut to form a fret work design (fig. 105). Each area to be cut out must first be drilled to accommodate the blade of the jewelers saw. Make a dent near one edge of the area, and resting a small drill (about No. 54) in this depression, drill a hole through the metal. Enlarge the hole with a heavier drill and saw out the area in the manner described at the beginning of the chapter.
(2) Finally, metal may be decorated by etching it with various acids (fig. 106). As this method requires experience and fairly extensive equipment it will only be outlined here. The technique consists of eating with the acid, or mordant, either the design or the background surrounding it. All parts of the article which are not to be etched are covered with a protective "resist" so that only the exposed surface is attacked by the acid. The metal must first be thoroughly cleaned and polished with steel wool. All areas which are to be protected are then coated with a black asphaltum varnish brushed on evenly and allowed to dry (fig. 107). Prepare the mordant in an earthenware or enameled container. Always put the water in first and add the acid gradually. For copper and brass, a good solution is one part nitric acid in two parts water. The mixture should be strengthened for silver, weakened for pewter. Aluminum requires a perchloride of iron (also called chloride of iron) solution. Mix in the proportion of 1 ounce, dry measure, of the acid to 1 ounce, liquid measure, of water. Place the varnished article in the etching bath and watch it carefully. If no bubbles appear on the exposed metal, the solution is too weak and must be strengthened. If the mordant shows excessive action it must be further diluted or it will undercut and eat through the resist. Aluminum must be removed frequently from the acid and rinsed in water before returning. When the surface has been etched to the required depth, remove the object, wash in cold water and dry. Dissolve the asphaltum varnish with turpentine and polish the un-etched portions of the piece as described above.