The important exception to the rule that
metals form protective surface coatings is
iron, which rusts in the presence of air and
moisture. The orange complex of ferric oxide
and water (Fe 2 O 3 • 2 O) is a loose powder
rather than a continuous film, and so does not
protect the metal surface from further contact
with the air. Unless it’s protected by some
other means, iron metal will corrode
continuously (this is why pure iron is not
found in nature). Efforts to make this cheap
and abundant element more resistant to
rusting resulted in the 19th century in the
development of stainless steel, an iron-carbon
alloy that — in cookware — is formulated
with about 18% chromium and 8–10% nickel.
Chrome is synonymous with bright and
permanent shininess because chromium is
extremely prone to oxidation and naturally
forms a thick protective oxide coat. In the
stainless steel mixture, oxygen reacts
preferentially with the chromium atoms at the