Determining if a mug is safe involves checking for both physical integrity and chemical composition. First, look for a "Food Safe" or "Lead-Free" label on the bottom of the mug; modern mass-produced ceramics in the US and EU are strictly regulated, but vintage or artisanal pottery from countries with looser standards may contain lead or cadmium in the glaze. You can use a lead-test swab kit if you are concerned about an older or imported piece. For microwave safety, look for the "Microwave Safe" symbol (usually three wavy lines); if a mug lacks this, you can test it by microwaving it alongside a glass of water for 30 seconds—if the mug itself gets very hot while the water stays cool, it is absorbing energy and is not microwave-safe. Additionally, check for cracks, chips, or "crazing" (tiny spider-web cracks in the glaze); these areas can harbor bacteria or allow chemicals to leach from the clay body into your drink. Finally, ensure the mug does not have any metallic trim (gold or silver leaf), as these will spark in the microwave and can damage the mug's finish and your appliance.