Stainless steel cookware sets are mostly resistant to stains, but there is always a possibility for burned food sticking, white buildup of calcium from hard water and rainbow-like discoloration from overheating. You can fix this by boiling a mixture of water and vinegar and then washing with hot, soapy water or by scrubbing with a non-abrasive sponge and baking soda. For stubborn stains, use a nylon scouring pad or a soft bristle brush and a stainless steel cleanser such as Bar Keepers Friend. Avoid abrasive cleaners, adding salt to water before it is boiling, washing the pan before it cools, and cooking frozen food.