Copper
The finest antique copper pieces are very heavy, show little wear, and have no dings or dents. The color should run to red rather than pink, which is a sign that the piece is new and probably has an aluminum core. Copper cookware should always be lined with tin, stainless steel, or some other nonreactive metal to prevent the potentially toxic reaction that occurs when acidic foods come into contact with copper.

"A just-polished piece of copper is really bright, almost too bright," says Fritz Karch, collecting editorial director at Martha Stewart Living. "But after a couple of days, the glow turns beautifully rosy." He suggests polishing quarterly to keep copper glistening -- unless, of course, you prefer a more subdued patina, which requires less frequent attention. Several copper polishes are available; choose one that gives you the glow you're looking for. Copper pieces polish up rosier with Red Bear, a favorite brand of Martha's, while solutions such as Twinkle, Noxon, and Brasso make the metal go gold. (Red Bear is available through specialty dealers; the others are sold at hardware and kitchen-supply stores). If a piece suffers a burned spot, Copper Brite can restore it to its original luster. For a natural polish, apply a wash of lemon juice or white vinegar and a sprinkling of coarse salt with a soft brush.