Bronzing. This is the process of giving a bronze-like or an antique metallic appearance to the surface of copper, brass, and other metals. This is generally effected by the action of some substance which combines with and changes the nature of the surface of the metal. The application of powdered bronzing substances, made to adhere by sizing, etc., to the surface of other material than metal, such as wood, plaster, etc., is termed surface bronzing. (See Nos. 3382 (To Color Brass), etc..)

3772. Brown Bronzes for Medals, etc.

3772.      Brown Bronzes for Medals, etc.. Take a wine-glass of water, and add to it 4 or 5 drops nitric acid; with this solution wet the medal (which ought to have been previously well cleaned from oil or grease) and then allow it to dry; when dry impart to it a gradual and equable heat, by which the surface will be darkened in proportion to the heat applied.

3773. Bronzing with

3773.    Bronzing with. Crocus. Make a thin paste of crocus and water; lay this paste on the face of the medal, which must then be put into an oven, or laid on an iron plate over a slow fire; when the paste is perfectly reduced to powder, brush it off and lay on another coating; at the same time quicken the fire, taking care that the additional heat is uniform; as soon as the second application of paste is thoroughly dried, brush it off. The medal being now effectually secured from grease, which often occasions failures in bronzing, coat it a third time, but add to the strength of the fire, and sustain the heat for a considerable time; a little experience will soon enable the operator to decide when the medal may be withdrawn; the third coating being removed, the surface will present a beautiful brown bronze. If the bronze is deemed too light the process can be repeated.

3774. Bronzing with Black-Lead

3774.     Bronzing with Black-Lead. After the medal has been well cleaned from wax or grease, by washing it in a little caustic alkali, brush some black-lead over the face of it, and then heat it in the same way as described in No. 3773 for crocus; or a thin paste of black-lead may be used, and the processes already referred to be repeated until the desired brown tint is obtained. In this kind of bronze a little hematitic iron ore, which has an unctuous feel, may be brushed over the face of the bronze, by which a beautiful lustre is imparted to it, and a considerable variety in the shade may be obtained. In the brown bronzes the copper is slightly oxidized on the surface.

3775. Plumbago Bronze

3775.    Plumbago Bronze. This bronze is obtained by brushing the surface of the medal with plumbago, then placing it on a clear fire till it is made too hot to be touched, and applying a plate brush so soon as it ceases to be hot enough to burn the brush. A few strokes of the brush will produce a dark brown polish, approaching black, but entirely distinct from the well known appearance of black-lead. If the same operation is performed on a medal that has been kept some days, or upon one that has been polished, a different, but very brilliant tint is produced. The color is between red and brown. The richness of color thus produced is by many preferred to the true dark brown.