🔰 All glass cups contain some impurities, one of which is nickel sulfide. Most nickel sulfide particles in glass do not cause problems and are stable. However, in some cases, without external force or any stress If heat is applied to the glass, it causes the sudden breakage of tempered glass, or so-called suicide of the glass. This breakage is usually seen in the form of a butterfly wing in the glass.
🔰 In the process of heating the glass in the furnace, the nickel sulfide particles change from their normal structure at low temperature to the crystal structure at high temperature, and because the cooling is done quickly, the nickel particles are not able to return to their original state. As a result, after the passage of time, these particles tend to return to their normal structure, but with a volume increase of about 2 to 4%, and this volume increase is the main reason for the suicide of tempered glass.