This invention relates to a flat float glass that can be prestressed or transformed into a glass ceramic with high quartz mixed crystals or keatite mixed crystals. To eliminate undesirable surface defects during floating and to achieve superior characteristics of the glass or of the glass ceramic, in particular with regard to a low coefficient of thermal expansion and high light transmittance, the glass has a concentration of less than 300 ppb Pt, less than 30 ppb Rh, less than 1.5 wt. % ZnO and less than 1 wt. % SnO.sub.2, and is refined during melting without the use of the conventional fining agents arsenic oxide and/or antimony oxide.