Editing Cookware and bakeware (section)

====Copper====
[[Copper]] provides the highest thermal conductivity among non-[[noble metal]]s and is therefore fast [[heat]]ing with unparalleled heat distribution ''(see: [[Copper in heat exchangers]]).'' Pots and pans are [[cold forming|cold-formed]] from copper sheets of various thicknesses, with those in excess of 2.5&nbsp;mm considered commercial (or ''extra-fort'') grade. Between 1&nbsp;mm and 2.5&nbsp;mm wall thickness is considered utility (''fort'') grade, with thicknesses below 1.5&nbsp;mm often requiring [[tube beading]] or [[edge rolling]] for reinforcement. Less than 1mm wall thickness is generally considered decorative, with exception made for the case of .75–1&nbsp;mm [[planishing|planished]] copper, which is [[work hardening|hardened]] by hammering and therefore expresses performance and strength characteristic of thicker material.

Copper thickness of less than .25&nbsp;mm is, in the case of cookware, referred to as [[foil (metal)|foil]] and must be formed to a more structurally rigid metal to produce a serviceable vessel. Such applications of copper are purely aesthetic and do not materially contribute to cookware performance.

Copper is reactive with acidic foods which can result in corrosion, the byproducts of which can foment [[copper toxicity]]. In certain circumstances, however, unlined copper is recommended and safe, for instance in the preparation of [[meringue]], where copper ions prompt proteins to denature (unfold) and enable stronger protein bonds across the sulfur contained in egg whites. Unlined copper is also used in the making of preserves, jams and jellies. Copper does not store ("bank") heat, and so thermal flows reverse almost immediately upon removal from heat. This allows precise control of consistency and texture while cooking sugar and pectin-thickened preparations. Alone, fruit acid would be sufficient to cause leaching of copper byproducts, but naturally occurring fruit sugars and added preserving sugars buffer copper reactivity. Unlined pans have thereby been used safely in such applications for centuries.

Lining copper pots and pans prevents copper from contact with [[acid]]ic foods. The most popular lining types are [[tin]], [[stainless steel]], [[nickel]] and [[silver]].

The use of tin dates back many centuries and is the original lining for copper cookware. Although the patent for [[canning]] in sheet tin was secured in 1810 in England, legendary French chef [[Auguste Escoffier]] experimented with a solution for provisioning the French army while in the field by adapting the tin lining techniques used for his cookware to more robust steel containers (then only lately introduced for canning) which protected the cans from corrosion and soldiers from lead solder and [[botulism]] poisoning.

Tin linings sufficiently robust for cooking are wiped onto copper by hand, producing a .35–45-mm-thick lining.{{sfn|Hoare|1959|p=82}} Decorative copper cookware, i.e., a pot or pan less than 1&nbsp;mm thick and therefore unsuited to cooking, will often be [[electroplating|electroplate]] lined with tin. Should a wiped tin lining be damaged or wear out the cookware can be re-tinned, usually for much less cost than the purchase price of the pan. Tin presents a smooth crystalline structure and is therefore relatively non-stick in cooking applications. As a relatively soft metal abrasive cleansers or cleaning techniques can accelerate wear of tin linings. Wood, silicone or plastic implements are to preferred over harder stainless steel types.

For a period following the Second World War, copper cookware was [[electroplating|electroplated]] with a nickel lining. Nickel is harder and more thermally efficient than tin, with a higher melting point. Despite its hardness, it wore out as fast as tin, as the plating was 20 microns thick or less, as nickel tends to plate somewhat irregularly, and requires milling to produce an even cooking surface. Nickel is also stickier than tin or silver. Copper cookware with aged or damaged nickel linings can be retinned, or possibly replating with nickel, although this is no longer widely available. Nickel linings began to fall out of favor in the 1980s owing to the isolation of nickel as an allergen.

Silver is also applied to copper by means of electroplating, and provides an interior finish that is at once smooth, more durable than either tin or nickel, relatively non-stick and extremely thermally efficient. Copper and silver bond extremely well owing to their shared high [[Electrical resistivity and conductivity|electro-conductivity]]. Lining thickness varies widely by maker, but averages between 7 and 10 microns. The disadvantages of silver are expense and the tendency of sulfurous foods, especially [[Brassica oleracea|brassicas]], to discolor. Worn silver linings on copper cookware can be restored by stripping and re-electroplating.

Copper cookware lined with a thin layer of stainless steel is available from most modern European manufacturers. Stainless steel is 25 times less thermally conductive than copper, and is sometimes critiqued for compromising the efficacy of the copper with which it is bonded. Among the advantages of stainless steel are its durability and corrosion resistance, and although relatively sticky and subject to food residue adhesions, stainless steel is tolerant of most abrasive cleaning techniques and metal implements. Stainless steel forms a pan's structural element when bonded to copper and is irreparable in the event of wear or damage.

Using modern metal [[Thermocompression bonding|bonding]] techniques, such as [[Cladding (metalworking)|cladding]], copper is frequently incorporated into cookware constructed of primarily dissimilar metal, such as stainless steel, often as an enclosed diffusion layer (see ''coated and composite cookware'' below).