We work with boro-silikat-glass - hard glass. This is the same glass that is used for labratories equipment. This is very heat resistant. You may use it for cooking in the oven, like caseroles, or in the steamer or microwave. But be aware when taking it from the heat do not put it on cold metal, nor on wet towls. Remember when it is hot, do not shock it with cold water. You also may clean it in the dish-washer. You may light a candle in it, but be aware that the candle produces heat. Therefore hang the candle-holder on a metal wire and when placing it on the table, use a cork to protect the furniture.