Bronze disease

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Contributions by: Taryn Ricciardelli

Bronze disease refers to the disfiguration and/or corrosion of copper alloys caused by chlorides in the patina interacting with water and oxygen. The instability of bronze objects that were recently excavated in archaeological contexts can be attributed to corrosion processes forming cuprous chloride close the surface of the object and against unchanged metal Scott 1990. Bronze disease is usually visible as a light green, powdery substance on the surface of an artifact, however, it can lie dormant in archaeological objects until they are in an environment of increased relative humidity. Bronze disease is especially detrimental to copper alloys, as it is a cyclical chemical process, making it hard to stabilize a metal artifact once it has fallen victim to the disease Scott 1990.

Related Terms

bronze, copper alloy, discoloration, distortion, patina, powdering, relative humidity (RH), stabilizing, stain, warp (damage)

Synonyms in English

Translation

English bronze disease
French
Spanish
Portuguese doença do bronze
Italian
German
Arabic

Discussion

The treatments for bronze disease have been changing frequently, as more information on the related chemical processes are discovered and tested. As mentioned above, bronze disease is a cyclical chemical process in which the corrosion processes are accelerated as the object is introduced to moisture and oxygen, so the stabilization of bronze artifacts before they are exposed to the disease is crucial Scott 1990. MacLeod 1987 states that bronze disease is more rare in historical artifacts, as impurities in the metal inhibit copper(I) oxide’s function in corrosion processes. Madsen 1967 discusses using benzotriazole to stabilize bronze objects, though his predecessors were regularly soaking artifacts in sesquicarbonate or impregnating objects with paraffin. Sharma, Lal, and Nair 1995 recommend using zinc dust to stabilize bronze artifacts; in high humidities, zinc oxide failed as a treatment method, whereas zinc dust was effective in a number of environmental conditions. MacLeod 1987 suggests using alkaline dithionite along with subsequent mechanical cleaning for the most efficient removal of chlorides in the shortest amount of time. Unfortunately, some treatments that have been regularly used on bronze artifacts can have deleterious (or unaesthetic) chemical interactions (see D’Ars, Bellis, Lins, and Souza 2007 ’s discussion of AMT’s interaction with bronze). The most effective way to combat bronze disease is by controlling the relative humidity in an object’s environment. Although the situation varies according to exact material type and storage conditions, a relative humidity between 42% and 46% is recommended Scott 1990.

References

D'Ars F. Junior, João Cura, Vito M. De Bellis, Vanessa F. C. Lins and Luiz A. C. Souza. 2007. A Note on the Products of the Reaction of AMT with Bronze and with Three Corrosion Products of Bronze. Studies in Conservation 52(2):147-153.

MacLeod, Ian Donald. 1987. Conservation of Corroded Copper Alloys: A Comparison of New and Traditional Methods for Removing Chloride Ions. Studies in Conservation 32(1): 25-40.

Madsen, Brinch H. 1967. A Preliminary note on the Use of Benzotriazole for Stabilizing Bronze Objects. Studies in Conservation 12(4): 164-167.

Scott, David A. 1990. Bronze Disease: A Review of Some Chemical Problems and the Role of Relative Humidity. Journal for the American Institute for Conservation 29(2): 193-206.

Sharma, V.C., Uma Shankar Lal, and M.V. Nair. 1995. Zinc Dust Treatment: An Effective Method for the Control of Bronze Disease on Excavated Objects. Studies in Conservation 40(2): 110-119.


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