8989 Glue Water (Hard protective glue for crystals without glass back sheet) Item:JS78 Its ph value is up to 7 of high hardness, Transparent. This glue is used to protect the films of some crystals which are of irregular shapes without glass back sheet. The film is protected by this glue so it is not necessary to use the glass back sheet. Therefore, the image on the film will be kept away for damage or scratching and remains beautiful.