Last year I found out that during the communist era, when too much glass items were produced, they would be discarded into the foundations on building yet to be built. It would be done both with bad lots that had faults, but also with overproduction. This was a way of disposing of the glass, and keeping the prices up. Apparantly, when a power plant was built in the city of Liberec, bordering Jablonec, wagonloads of glass waste were taken into the city by train to put down at the foundation.

Below are pictures of a place were I could see this for myself. The first picture shows glass bits in a pile of dirt at a construction site. The second picture shows some of the glass I recovered from there, including whiteheart tubes yet to be made into beads.