Stoneware clay is very strong. It is fully vitrified (the surface is made glassy and non-porous) which gives it strength, durability and chip resistance. It can be safely used in: Dishwasher - Whilst Denby tableware is safe to use in a dishwasher, constant dishwashing may result in discolouration of product over time. We recommend using low temperatures and liquid detergents; Oven & Microwave for cooking and reheating food. Please note: Using microwaves as a means of warming empty dinnerware can cause damage to both your dinnerware and microwave and is therefore not recommended; Freezer for storing food. All pottery and china can crack if exposed to sudden changes in temperature, no matter how strong it is, so please do not take items from the freezer and put them straight into the oven or microwave or expose to direct heat sources such as the hob or grill.