Proper repair techniques for fixing cracked glass depend on the context and the severity of the crack; for example, a crack in a car's windshield can be treated with a filling product or the windshield can be replaced entirely while a cracked wine glass might be fixed with clear epoxy glue or may need to be discarded. Glass that will be used in the preparation or consumption of food or drink will need to be treated with a food-safe adhesive or sealant, and if this is not possible, it may be necessary to discard or repurpose the glass. In some cases, cracks in glass can spread even if repair steps are taken.
For cracks in glass used for electronics, such as the screen of a smartphone, the conventional wisdom is that the glass will need to be replaced. This is the best way to bring the technology back to full functionality without risking injury from glass shards and the sharp edges of glass cracks. The phone's screen can usually be replaced in a do-it-yourself fashion, but those who aren't experienced with working with technology and can't afford both a replacement screen, and a replacement phone if the repair goes wrong, may want to send the phone off for professional repair.