[cleansy]

That and producing these glasses with said technique is a lot more expensive. You need to heat up the glass and the potassium nitrate to 500C, mostly over hours because otherwise the glass breaks. Then you need to keep it for a couple of hours, then cool down slowly. What made the initial east german production work is, they did it on a large industrial scale, but even then the energy that you need makes the glasses quite expensive to produce. It's hard to justify buying 6-7€ for a regular drinking cup when a comparable form factor is 1€ or something in this region.