RATIO OF CAO K2O-GREATER-THAN-2 AS EVIDENCE OF A SPECIAL RHENISH TYPEOF MEDIEVAL STAINED-GLASS/

The chemical compositions of more than 300 medieval stained glass samp les of different local origin have been published so far. Regarding th eir characteristic components they can be classified into five types. About 80 % of all investigated samples proved to be potash-lime-silica glasses with roughly equal concentration of CaO and K2O (type 1). But a small group of little more than 20 samples gave a ratio of CaO/K2O > 2 (type 2), all but three of which had been taken from two churches of the Rhine region (St. Catherine Church Oppenheim and Cologne Cathed ral). Hence, it seems likely that a corresponding recipe was used ther e, which was nearly unknown elsewhere in Europe. Investigation of furt her objects of this region might be of interest for the history of tec hnology