Luminarc Vitro is made from Vitro-Ceramic, a unique material so heat resistant and durable that it was used by NASA in the design of Space Shuttle. Thanks to it's unique material Luminarc cookware makes cooking much easier as one dish can be used to prepare, cook, and serve and store your favorite meals. We guarantee that the vitroceramic in normal everyday household use retains its thermal performances. The vitroceramic cookware goes from and can be used in the freezer (resistant up to 35'C) and may resist progressively temperatures up to 800'C. This cookware can resist rapid temperature variations up to 450'C. To cook, we recommend to pre-heat the vitroceraminc cookware at a low temperature for 2 minutes before each use. You may then cook at a low temperature for an even heat distribution. The vitroceramic material retains heat for a long period of time. You can therefore let your water - based recipes stew at a very low temperature. You may even turn off the heat prior to finishing the cooking process, this will help you save energy and your vitroceramic cookware will do the rest. Vitroceramic is particularly adapted for cooking stews, soups, sauce, and water-based recipes. Before the first use, clean your product in soapy hot water and without any abrasive scourer. After each use, after a short cooling period set your product aside to cool for a short period, then let it soak in hot soapy water before cleaning. **DISCLAIMER** GLASS COOKWARE LIDS DO NOT FIT LIKE CAST ALUMINUM BODY DOES, SO LIGHT MOVEMENT OF LID WHEN CLOSED IS NORMAL. GOOD QUALITY CERAMIC GLASS CAN NATURALLY HAVE FINE LINES AND AIR BUBBLES.