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As a general rule, one must immerse, in a mikve, any glass or metal utensil or receptacle obtained from a non-Jew and to be used for preparing, serving, or eating food. (Source, source.) What if it's to be used for food, but the food isn't going to touch it directly? For example,
- a microwave-oven turntable on which one plans to put bread to defrost, but only on a paper towel so as not to dirty the turntable; or
- a toaster-oven tray on which one will heat food, but only on foil so as not to dirty the tray; or
- a metal bread basket in which one will serve bread, but only wrapped in a napkin for elegance.
Do such items require immersion?