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Bronze Characteristics and Uses

Blog Bronze Characteristics and Uses

Bronze is an alloy of copper which can vary widely in its composition. It is often used where a material harder than copper is required, where strength and corrosion resistance is required and for ornamental purposes. The variations in bronze (both in proportion and elemental composition) can significantly affect its weathering characteristics. “True” bronze is a combination of approximately 90% copper (Cu) and 10% tin (Sn), however there are three major classes or types of “bronzes” used in sculpture and construction.

They are:

  1. Statuary Bronze – approximately 97% copper (Cu), 2% tin (Sn) and 1% zinc (Zn); this composition is the closest to “true” bronze.
  2. Architectural Bronze – actually more of a “leaded brass”, is commonly composed of approximately 57% copper (Cu), 40% zinc (Zn) and 3% lead (Pb).
  3. Commercial Bronze – composed of approximately 90% copper (Cu) and 10% zinc (Zn). Traditionally, a copper alloy that contains zinc is a “brass”; a copper alloy which contains tin (not exceeding 11%) is a “bronze”.
    Bronze composition may vary significantly however, and contemporary bronzes are typically copper alloys which may contain silicon (Si), manganese (Mn), aluminum (Al), zinc (Zn) and other elements, with or without tin (Sn). Bronze in its “raw” state is a “pinkish”, salmon colored metal, however it is rarely seen in its pure state. Bronze usually exhibits some patination or corrosion so that its color normally ranges from lime green to dark brown. Exposed bronze undergoes continuous change and progresses through several predictable “stages” of oxidation and corrosion. The stages of bronze corrosion vary in duration and time of onset, based on many factors, including:
    1. Composition of the bronze
    2. Patination or other protective treatments applied at the foundry
    3. Weather
    4. Location and exposure to rain, sun, and other climatic conditions
    5. Atmospheric pollutants
    6. Scheduled maintenance/cleaning, and
    7. Adjacent materials including residual core materials.

TYPICAL USES

Statuary bronze is typically used in outdoor sculpture. Its forms are almost limitless since it may be cast in any shape for which a mold can be devised. The most common types of forms include the human figure, landscapes, battle scenes, animals, weapons, decorative elements such as stars, rosettes, etc., and plaques. Architectural bronze is typically used for: 1. door and window frames 2. door and window hardware 3. mail boxes and chutes 4. trim or rails, and 5. furniture hardware. As a general rule, architectural applications seek to preserve the natural, highly polished “pinkish” finish of raw bronze, in contrast to the patination of outdoor sculpture/ornament. This is achieved by the frequent polishing and oiling of bronze/brass decorative and structural elements, or their protection by the application of clear lacquers which must be renewed on a periodic basis. You can read more about bronze and the possible concerns it may present by visiting http://www.gsa.gov/portal/content/111994.