Any glassware with such cracks should be properly disposed of immediately. All glass tubing should be fire-polished. Never set hot glassware on cold surfaces or in any way change its temperature suddenly. If this fails, discard the glassware. Hot Glass Use care when working with hot glass.
Hot glass looks exactly the same as room temperature glass.
Do not leave hot glassware unattended, and allow ample time for the glass to cool before touching. Check the temperature of the glassware by placing your hand near, but not touching, the potentially hot glass. Have hot pads, thick gloves, or beaker tongs available for grasping hot glassware. Glass Tubing Breaking. Use gloves or towels to protect hands when breaking glass tubing.