All you wanted to know about using a sanitary silicone sealant to attach a heated bed that goes up to 140°C to a sheet of glass: https://tinystash.undef.im/il/4mhU1k1fCuNEnYEXPQ81kUNzSuHyCsW4SDtnHiH1jcT4ZipMVBNPem6S2UBbgSh1ngBUiosgQ6W6oqzE3RftefQC No idea about the nature of the burnt spots (i have no infrared thermometer to measure the uniformity of my PCB heater output), but it got really smelly. Will use a high temperature automotive sealant this time.