A hundred years ago SCHOTT delivered the first mirror blank for astronomy, a 720 mm crown glass disk for the Waltz telescope of the Landessternwarte Heidelberg, Germany. Since then significant progress has been made. Larger blanks out of optical glass have been followed by borosilicate disks. In the beginning of the 1970s SCHOTT introduced the zero-expansion glass ceramic ZERODUR. It has been applied for outstanding astronomy projects both ground based and space-borne. The paper gives an overview over the highlights of the last hundred years with some prospects to present and future developments.