According to the Dupont company, which makes Teflon, and the Calphalon company, which makes nonstick cookware, the new nonstick coatings on pots and pans stand up just fine to mechanical dishwashing. If a manufacturer says its pieces aren’t dishwasher safe, however, wash the cookware by hand with liquid detergent.
Unless coated with enamel, cast iron should never go in the dishwasher; water destroys the cookware’s seasoning and causes rust. Likewise, the protective coating on aluminum pans will wear quickly if machine washed, and copper is subject to pitting and tarnishing.
Stainless steel cookware takes dishwashing with no problem, although the finish may dull over time.
Glass pots and pans can go in the dishwasher, but non-phosphate detergents tend to leave a film on glass when used in hard water. Cookware with wooden handles should stay out; the handles may loosen and warp.
Repeated dishwashing of enameled pots and pans often dulls their color. They also are prone to chipping.