The crystal cup is also a glass. The most important component is silicon dioxide, but lead, barium, zinc, titanium and other substances are introduced. Because this kind of glass has high transparency and refractive index, its appearance is smooth and clear, so it is called crystal glass. If lead is introduced, it is lead crystal. The introduction of barium, zinc, titanium and other substances is lead-free crystal. How to distinguish between the two? Just feel. Because the thermal conductivity of crystal is stronger than that of glass, it should be cooler than touching glass when touching the crystal by hand. Second look at hardness. The hardness of natural crystal is 7, and the hardness of glass is 5, so the crystal can scratch the glass. Third look at refractive index. Raise a crystal cup and rotate it towards the light, you will find it is like a delicate handicraft, white, translucent, refracting the charming multicolored light, because the crystal can absorb the luster, even ultraviolet, and ordinary glassware There is no gloss and no refraction. Four listen to the sound. Tap lightly or hit the vessel with your fingers, the crystal glass vessel can emit a crisp and crisp metallic sound, and radiate a beautiful aftertaste in the breath, while ordinary glass vessels only have a stuffy "click, click" sound.