Once the Stained Glass Designs were approved, it was time to select glass. This was made much more difficult than usual due to diminishing availability of European mouthblown glass. The Polish factory had already closed thanks to the severe restriction of natural gas that's resulted from Putin's ghastly war in Eukraine. The only remaining source, in Germany, has had to curtail its production.
See "Blowing Sheets of Glass" & "Glass Types" under the "Resources" tab above for more about mouthblown glass.