The choice of method to be used in restoring a bronze depends partly on the extent and kind of corrosion present, and partly on the result which the owner desires. One must decide between attempting to restore the original bright lustrous surface of the bronze or removing enough of the corrosion to reveal the shape and detail of the object while retaining some patina as evidence of age and place of excavation. It is a most delicate problem, involving the nature and condition of the object, and the state in which it will prove of greatest value, aesthetically and archaeologically.
There are three methods which the restorer may use, either singly or in a combination. First is the abrasive or mechanical, in which the corrosion may be scraped, chiselled or rubbed away with abrasives until the original shape and detail of the object are revealed. The second is the chemical, in which undesirable corroded surface is dissolved chemically. The third is the electrolytic process, in which the object is treated in such a way that the corrosion process is inverted and the minerals returned to a metallic condition. Though involving artistic problems, these processes are scientific and best discussed by scientific specialists. A bibliography is given for those who are interested in more detailed information.
It is safe to say that most ancient bronzes have been restored. One way of telling whether or not they have been restored, either mechanically or chemically, is by studying the deep undercuts, where at least a portion of the corroded surface erally visible. The "Greek Horse" from the Metropolitan Museum (No. 81) shows a more corroded surface in the nostrils than on the smoother surface, while the "Sleeping Eros" (No. 95) from the same museum shows a rougher corrosion left on the rock to contrast with the smoother, more thoroughly cleaned surfaces of the child's body. These examples may serve to explain rather crudely how the restorer's problem involves aesthetic as well as scientific decisions.
Fink, Colin G. and Eldredge, Charles H., RESTORATION OF ANCIENT BRONZES AND OTHER ALLOYS, New York, 1925.
Nichols, Henry W., RESTORATION OF ANCIENT BRONZES AND CURE OF MALIGNANT PATINA, Chicago, 1930.
Fink, Colin G., "Corrosion and Restoration," under "Bronze and Brass Ornamental Work," in the ENCYCLOPAEDIA BRITTANICA, 14th edition.
Gettens, R. J., "Copper and Bronze Objects from Nuzi," TECHNICAL STUDIES, vol, I, no, 3.
Fink, Colin G. and Polushkin, E. P., "Microscopic Study of Ancient Bronze and Copper," METALS TECHNOLOGY, vol. III, no. 2, February 1936. (A list of nearly a hundred items on bronze corrosion will be found in the bibliography appended to this article.)