On food and cooking the science and lore of the kitchen ( PDFDrive ) 1483

thesurfaceofmetals,sothatthemetalscan
dothejobofdistributingtheheatevenly.
SpontaneousCeramicCoatingsonMetalsIt
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
exposedtotheair,thesurfaceatomsundergo
a spontaneous reaction with atmospheric
oxygen to form a very stable metal oxide
compound. (The discoloration on silver and
copper that we calltarnish is a metal-sulfur
compound; the sulfur comes mainly from air
pollution.) These oxide films are both
unreactiveandfairlytough.Aluminumoxide,
whenitoccursincrystalsratherthanonpans,
makesuptheabrasivecalledcorundum,andis
also the principal material of rubies and
sapphires (the gem colors come from
chromium and titanium impurities). The


problemisthatthesenaturalcoatingsareonly
a few molecules thick, and are easily
scratched through or worn away during
cooking.
Metallurgistshavefoundtwowaystotake
advantageofmetaloxidationatthepan
surface.Thefilmoveraluminumcanbemade
uptoathousandthofaninch/0.03mmthick,

andsofairlyimpervious,byachemical
treatment.Andironcanbeprotectedby
mixingitwithothermetalsthatforma
tougheroxidesurfaceandsoproducestainless
steel(p.791).
Herearebriefdescriptionsofthematerials
fromwhichmostkitchenutensilsaremade
today,andtheirparticularadvantagesand
disadvantages.
Ceramics

Earthenware,Stoneware,GlassCeramics
arevaryingmixturesofanumberofdifferent