Abstract A revised glass annealing method is presented that results in the separation of tempered glass from the other common glass types. The method uses a temperature programmable muffle furnace that allows a very slow annealing process. The possibility of separating bottle glass from laminated windshield glass emerged. The ability to classify small pieces of glass removed from clothing as to type increases the value of existing glass databases compiled by forensic scientists and, thus, the value of glass evidence in the courts.