Glassware is mostly made of soda lime silicate glass, colorless and transparent vessels, and the iron content in the glass is generally less than 0.02%. A coloring agent is added to the glass raw material to obtain a colored glass; and an opacifying agent is added to obtain an opaque glass (see glass manufacturing). High-grade artware such as goblets, perfume bottles, fruit bowls, etc., which are used to make honing cars, use potassium lead silicate glass, also known as lead crystal glass. This kind of glass contains PbO, which has high refractive index and dispersion. It is especially bright when grinding the facet, has a high specific gravity, and makes a crisp sound when struck. More than 30% of PbO is full lead crystal glass, including PbO 24 to 30% is medium lead crystal glass, PbO 18% or less is low lead crystal glass, and BaO containing bismuth crystal glass. Products such as cooking utensils such as coffee pots are made of heat-resistant borosilicate glass, which has a low coefficient of thermal expansion and is resistant to rapid temperature change. Glass-ceramics have better heat resistance and temperature-resistant variability, and are mechanically strong, making them suitable for the manufacture of simmered vessels and utensils that are often washed in hotels.