the surface of metals, so that the metals can do the job of distributing the heat evenly Spontaneous Ceramic Coatings on Metals It turns out that most of the metals commonly used in kitchen utensils naturally cover themselves with a very thin layer of ceramic material Metallic electrons are mobile, and oxygen is electron-hungry When metal is exposed to the air, the surface atoms undergo a spontaneous reaction with atmospheric oxygen to form a very stable metal oxide compound (The discoloration on silver and copper that we call tarnish is a metal-sulfur compound; the sulfur comes mainly from air pollution.) These oxide films are both unreactive and fairly tough Aluminum oxide, when it occurs in crystals rather than on pans, makes up the abrasive called corundum, and is also the principal material of rubies and sapphires (the gem colors come from chromium and titanium impurities) The problem is that these natural coatings are only a few molecules thick, and are easily scratched through or worn away during cooking Metallurgists have found two ways to take advantage of metal oxidation at the pan surface The film over aluminum can be made up to a thousandth of an inch/0.03 mm thick, and so fairly impervious, by a chemical treatment And iron can be protected by mixing it with other metals that form a tougher oxide surface and so produce stainless steel (p 791) Here are brief descriptions of the materials from which most kitchen utensils are made today, and their particular advantages and disadvantages Ceramics Earthenware, Stoneware, Glass Ceramics are varying mixtures of a number of different ... tougher oxide surface and so produce stainless steel (p 791) Here are brief descriptions of the materials from which most kitchen utensils are made today, and their particular advantages and disadvantages... surface The film over aluminum can be made up to a thousandth of an inch/0.03 mm thick, and so fairly impervious, by a chemical treatment And iron can be protected by mixing it with other metals that form a...problem is that these natural coatings are only a few molecules thick, and are easily scratched through or worn away during cooking Metallurgists have found two ways to take advantage of metal oxidation at the pan