Alloy: A mixture of two or more materials, at least one of which is a metal. For example, steel is an alloy of iron and carbon.
Amalgam: An alloy of mercury and another metal. Most metals can mix with mercury (are soluble in mercury) but some, such as iron, cannot.
Anode: A metal or other conductor connected to the positive terminal of a battery or DC power supply. The anode is positively charged to make it oxidizing, usually for the purpose of dissolving metal into a plating solution by converting it into a water-soluble cation (a positively charged ion). In the plating process metal cations are reduced at the cathode to become neutral metal atoms again.
Catalyze: To increase the rate of a reaction by adding a substance, called a catalyst. The catalyst is not consumed in the reaction. In unintentional patination of bronze, chloride ions are often the catalyst since they increase the rate of corrosion. Because the initial product of the corrosion reaction, CuCl, can react with other pollutants and liberate chloride ions, which allows the corrosion process to start anew, it is a catalytic reaction.
Cathode: A metal or other conductor attached to the negative terminal of a battery or DC power supply. The cathode is negatively charged; it is the source of electrons for reduction reactions during electroplating. The object to be plated is attached as the cathode and metal ions produced at the anode are reduced at the cathode, thereby coating the object.
Damascene: In addition to the metal inlay technique described in detail in this text, damascene also refers to a steel alloy of high and low carbon steel—sometimes called “Damascus steel”—used chiefly to make swords. When high and low carbon steel are forged together the finished blade has a distinctive swirling pattern resembling the highly intricate, inlaid designs produced by the damascene technique, which is why this steel alloy has the same name.
Disproportionation Reaction: A reaction in which a single substance is both oxidized and reduced.
For example copper (I) may disproportionate into copper (0) and copper (II), as shown in this equation: 2 Cu+ → Cu0 + Cu2+
Electron: The name given to a negatively charged wave/particle. Electrons can be given off by atoms or molecules in oxidation processes or accepted during reduction processes. Electrons are not equivalent to negative ions.
Gilding: The process of applying gold over a substrate. The substrate may be another metal or may be wood, ceramic, etc. Gilding methods described in this publication include electroplating, displacement plating, mercury gilding, and the use of leaf and foils.
Ion: The term that describes positively or negatively charged atoms or molecules. Ag+ is called a silver ion. Cu+ and Cu2+ are both called copper ions. Cl- and SO42- are chloride and sulfate ions, respectively. We also describe ions as positive ions or cations (if they carry a positive charge) or negative ions or anions (if they carry a negative charge).
Metal: Chemically, metals are described as being reactive, often giving up one or more electrons in a reaction. It is uncharged metals, in bulk, that have the physical properties generally associated with metals: lustrous, malleable, conductive, and ductile. A complete list of metals may be found on the periodic table.
Metal Hardness: The physical property of a metal, which gives it strength (the ability to resist being bent, broken, or having its shape changed). The greater the hardness of the metal, the greater resistance it has to deformation.
Metal Salt: An oxidized form of a solid metal. The metal ions in metal salts carry a positive charge and when paired with negatively charged ions, a crystalline solid forms. Many minerals are metal salts.
Oxidation: The electrochemical process that results in the loss of an electron from an atom or molecule. For example, when metallic copper Cu0 loses an electron and becomes Cu+ it has been “oxidized.” But, another atom or molecule must accept the electron that copper has given up to balance the reaction. In the example illustrated below, oxygen molecules accept the electron from copper, and copper oxide (composed of oxidized copper and reduced oxygen) forms. Corrosion layers and patinas on metals and metal salts are all oxidized forms of metals, which are formed through oxidation and reduction reactions, which are called “redox reactions.” Another example: in silver chloride, AgCl, the silver atom is in the plus one oxidation state, Ag+; and in copper sulfate, CuSO4, the copper atom is in the plus two oxidation state, Cu2+.
Redox: The term used to describe paired reduction and oxidation reactions.
Reduction: The electrochemical process that results in the gain of an electron from an atom or molecule. Reduction is the opposite process from oxidation. For example, in the case of Cu2+, the copper ion may gain one electron to become Cu+ and it may gain a second electron to become Cu0. Another example: when Ag+ is reduced (by gaining an electron) to become Ag0, it becomes metallic silver.
Solder: A metal alloy, traditionally of lead and tin, having a low melting point. Solder is commonly used to join separate metal pieces together.
Substrate: The material that forms the body or base of an object is called the substrate. Substrates used in works of art include canvas (for paintings), metals (for sculpture), wood (for furniture), fabric (for costumes), paper (for drawings and photographs), and many more.
Vickers Scale: The Vickers Scale is based on the results of the Vickers Hardness Test, one of a few standard tests to measure metal hardness. In this test, an indenter made of a single diamond, shaped like an inverted square pyramid, is pressed onto a flat metal surface. Depending on the force with which the indenter was pressed and the hardness of the metal, the metal surface will indent to a greater or lesser extent. The difference in the indented area on different metals provides a means of comparing and ranking their hardness.