Aspects of bronze patina and its treatment

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Publication Type:

Journal Article

Authors:

Organ, R.M.;

Source:

Studies in conservation, Volume 8, Number 1, p.1-9 (1963)

Keywords:

bronze, conservation, corrosion, treatment

Abstract:

The substance of a lecture delivered at a Conference on the Conservation of Metallic Antiquities held at Poznan, Poland in 1962. One mechanism for the under-surface corrosion of bronze is described in which strata of cuprous chloride, cuprous oxide, and basic copper carbonate are found in succession from the metal to the surface. To illustrate this the corrosion structure of a pair of copper chisels (Jericho, 6000 B.C.) is examined. Here the original surface is preserved in a line of cleavage within the cuprous oxide layer. The cuprous chloride found next to the metal quickly forms bulky basic cupric chloride ("bronze disease") on exposure to high humidity. To cure this form of active, unstable, corrosion there are three methods, apart from ensuring that humidity remains below 40-50% R.H. (which will prevent the formation of basic cupric chloride). (1) Thorough chemical and electrochemical stripping of all corrosion products, where this is permissible. (2) Conversion of cuprous chloride to the harmless cuprous oxide by prolonged hydrolysis in alkaline solution (sodium sesquicarbonate). (3) Treatment of spots of bronze disease by excavation followed by the application of silver oxide powder. G. Thomson