Question

why did ancient glass batches contain so much alkali content?

Answer 1

In ancient times the composition of vast variety of glass is closley related to the crotectic trough leading from the eutectic region of the soda-lime -silica system towards more calcium rich compositions.chemcial compositions have mainly been used as descriptive tool to charectarize the different types of glasses.

In that times, batches were limited to their primary base glasses, that is pure soda as alkali with out K2O , pure silica without Al2O3, and pur lime with fixed level of MgO.and primary consitituent is silica.