surface or structural changes caused by a chemical between the material and its environment.
Synonyms in English
decomposition, deterioration, decay, degeneration, erosion, rust, oxidation
Corrosion is defined as the wearing away or destruction of a material, usually associated with metal, by a chemical agent or process.
Tools, jewelry, toys, sculpture, tableware, furniture, kitchenware, and almost any other item can be made from metal. Metals—gold, silver, copper alloy, pewter, and iron to name just a few—are produced from ores that are found in nature and are processed, or smelted, from a stable mineral state to a less stable metallic state. Almost every metal material you will encounter will be an alloy—a mixture of more than one metal. Corrosion easily targets these metals because the moment metal is used to manufacture an object, the various metals and their alloys utilized begin to react to their environment in an effort convert themselves into more stable compounds. (Hamilton) While “noble metals” such as gold and silver corrode at a lesser rate, “baser metals” of iron, tin, and lead corrode at a much higher rate. The appearance of corrosion will vary with each metal involved.
Metals also corrode on contact with waters, acids, bases, salts, oils, aggressive metal polishes, and other chemicals. Environments that also contain higher amounts of oxygen and moisture, for example salt and freshwater areas, also can increase a metal’s corrosion rate. Environments need to be controlled as far as relative humidity and temperature. You want to limit the amount of said moisture in the air with the humidity being below 55 percent in areas that store your metal objects. Another important aspect is to prevent extensive air pollution in your metals storage area. Fine dust and debris in the air can accumulate on metal surfaces, attracting moisture and encouraging corrosion. Also gases in the air can attack metals; gasses from car exhaust, rubber products, and cigarette smoke cause silver and copper alloys to discolor and corrode. Acidic gasses from wooden cabinets and cases can also cause metal corrosion. Vapors produced by plywood and other products that off-gas formaldehyde cause lead alloys and other metals to corrode, forming wispy white crystals often confused with mold growth. Keeping metal objects in a clean, dry, safe environment can prevent deterioration from environmental sources.
Preventative care should be utilized to help alleviate the threat of corrosion. Metals should be stored in metallic cabinets and shelving as opposed to wood products which can emit dangerous acids. Acid-free boxes and tissue can be used as wrappings and protectants as well as clean, soft cotton clothes. Another source of risk to metals is improper handling and cleaning. The acid and oils secreted from human skin can be deposited on the metal during handling with the actual fingerprint of the handlers’ fingers sometimes imprinting on the metal. Just like any object, clean gloves or clean hands should always be utilized when handling. It is also not good practice to constantly polish or aggressively clean metals. Being as careful as possible is the best policy for the handling of all objects.
Some signs of corrosion include: 1) flaking or powdering of the metal surface, 2) fragments surrounding the object, 3) depressions on the metal surface (iron), 4) orange spots in these depressions (iron), 5) “sweating” or “weeping”- brown, yellow, or orange droplets on the metal surface (iron), 6) “bronze disease” or light green powder on the surface (copper/copper alloys), 7) loose white powder on surface (lead/pewter), and 8) tarnish and characteristic “rotten egg smell” (silver).
Canadian Conservation Institute. "Recognizing Active Corrosion: CCI Notes 9/1." Canadian Conservation Institute. 2007.
Corrosion. Thesaurus.com. Roger's 21st Century thesaurus, Third Edition. Philip Lief Group. 2009
“Caring for Your Treasures: Metal Objects” (2016) AIC: American Institute for Conservation of Historic and Artistic Works. http://www.conservation-us.org/about-conservation/caring-for-your-treasures/metal-objects#.Vw0OSfkrKUk
Getty Research Institute. Art & Architecture Thesaurus Online Corrosion. 2004
Hamilton, Donny L. (1999) “Methods of Conserving Archaeological Material from Underwater Sites.” Anthropolgy 605: Consevration of Archaelogoical Resources I. Texas A&M University. http://nautarch.tamu.edu/CRL/conservationmanual/ConservationManual.pdf
Logan, Judy. (2007) “Recognizing Active Corrosion.” Canadian Conservation Institute (CCI) http://canada.pch.gc.ca/eng/1439925170338
Museum of Fine Arts Boston. Conservation & Art Materials Encyclopedia Online (CAMEO). 2013.
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