A process for forming glass or glass ceramics is disclosed, wherein a glass ceramics form (12) is made from a starting glass by molding, which is transformed by a heat treatment into a keatite glass ceramic comprising predominantly keatite mixed crystals. With such a keatite glass ceramics form (12) formed bodies can be prepared from blank parts by sagging under gravity force at a temperature above the glass transition temperature of the blank part (14) (FIG. 1).