Submerge the trays in a single layer under warm, soapy water. Use a soft cloth to scrub off built up dirt. If the trays are engraved, use a soft bristle toothbrush to scrub the engraved areas. Rinse the trays in cool water.
Dissolve and boil 2 tablespoons cream of tartar in 1 quart water. Pour the solution over your trays and let it sit for 10 minutes. Scrub the trays with the soft cloth and soft bristle brush and rinse them with cool water.
Scrape off any rust spots gently with a wadded up ball of aluminum foil.