Alloys are a combination of two or more pure metals, often gold and silver. Sterling silver is an alloy of 925 parts fine silver and 75 parts copper, which makes the metal stronger and more durable to wear.
The first human tools, implements and weapons were likely made from native copper (i.e., untreated copper ores), but they were likely too brittle to be hammered into shape without heating and annealing. It was only later that smelting was developed, which allowed for the purification of native copper and its use for a variety of applications.
Smelting and annealing were crucial to the development of true metallurgy, since copper could be heated, then hammered into shapes and cooled to form metals with various properties. Copper was then combined with other elements to produce different alloys, such as brass or bronze.
Refinement and smelting are also important in the production of electrical systems that generate power from renewable resources. The most common copper use is as cathodic material in rechargeable batteries.
Corrosion is a natural characteristic of metals. When a base metal, such as copper, is joined with a noble metal, such as silver, in the presence of an electrolyte, it forms an electrolytic cell that in essence is a battery. This process causes corrosion, which can lead to loss of color, tarnish and the formation of pits or other surface defects.
Silver plating is a method of introducing silver onto the surfaces of copper, brass or other metals to provide a silvery appearance to objects. Before silvering, the metal surfaces should be prepared by removing most of the oxide film with an abrasive slurry of calcium carbonate or 1 mm aluminum oxide and water.