Bronze and Brass Alloys
Brass, Commercial Bronze
Brass, known today as Commercial Bronze, is typically an alloy of 90% copper and 10% zinc. Some bronze alloys range from 88% to 95% copper and may contain up to 12% tin instead of zinc, with phosphorus, manganese, aluminum, or silicon as trace additives. Fun fact about bronze: The earliest tin alloy bronzes were discovered in the 4th millenium B.C.E. in Luristan (present day Iran) and in Mesopotamia (Iraq). From Italian bronzo or Persian berenj meaning brass. The reasons for the decline of tin in bronze alloys are complex and related to trade. Tin was a very important trade commodity in the ancient world. In later times zinc came into use instead of tin in bronze alloys.
Many stamps and dies used in jewelry-making are made of bronze. Bronze is an excellent metal choice for jewelry-making tools because it will not generate sparks when hammers or mallets are struck against its hard surface. This is where the metal qualities of bronze differ from steel. Also, bronze will suffer only surface corrosion making it a suitable metal for use in outdoor sculptures.
The Oligodynamic Effect of BrassThe Oligodynamic effect is an interesting quality of brass (copper/zinc alloy).
The oligodynamic effect, from the Greek oligos meaning 'few' and dynamis meaning 'force', was discovered in 1893 by Swiss scientist Karl Wilhelm von Nägeli.* The oligodynamic effect is a toxic action of metal ions on living cells, algae, molds, spores, fungus, viruses, prokaryotic, and eukaryotic micro-organisms, even in relatively low concentrations, hence its name. Ions of mercury, silver, copper, iron, lead, zinc, bismuth, gold, aluminum, and other heavy metals exhibit a similar antimicrobial effect.
Science is unaware of the exact mechanism causing oligodynamic action. Data from silver suggest that these ions denature the proteins (enzymes) of the target cell or organism by binding to reactive groups resulting in their precipitation and inactivation. Silver inactivates enzymes by reacting with the sulfhydryl groups to form silver sulfides. Silver reacts with the amino-, carboxyl-, phosphate-, and imidazole-groups and diminishes the activities of lactate dehydrogenase and glutathione peroxidase. Gram-positive and gram-negative bacteria are affected but they can develop a heavy metal resistance. In the case of silver, gram-positive and gram-negative bacteria develop a silver resistance. Viruses are not very sensitive. The toxic effect is fully developed often only after a time span of several hours. It is interesting to note that sterling silver (.925 pure) in solid form is a very porous metal and is not a good choice for use in nose rings and other body piercing jewelry. This is because organisms can be trapped in the jewelry due to the porosity of the metal and such piercing never fully heal.
Certain metals, brass and copper for example, are more poisonous to bacteria than other metals, such as steel and aluminum. This is a reason that they are chosen for use in mineral sanitizers for swimming pools and spas.
Many infectious diseases are spread by doorknobs since humans are lax at hand washing.1 Brass doorknobs automatically disinfect themselves in about eight hours. Stainless steel and aluminum knobs never disinfect themselves. Brass doorknobs tend to be more sanitary and used in hospitals, nursing homes, doctor's offices, clinics, and large public buildings.
Silver is capable of rendering stored drinking water potable for a long period of time (several months). For this reason, water tanks on ships and airplanes contain silver. Silver or silver compounds are used externally in wound and burn treatments.2
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* Original article by Nägeli: v. Nägeli K.W. 1893. Über oligodynamische Erscheinungen in lebenden Zellen. Neue Denkschr. Allgemein. Schweiz. Gesellsch. Ges. Naturweiss. Bd XXXIII Abt 1.
1. Doorknobs: A Source of Nosocomial Infection?