Large glass objects (such as a glass sphere/crystal ball over 6 inches diameter) need to be cooled in a kiln slowly over many days.
MineMy crystal ball is larger than that, which is why it cost $600 thirty years ago.
In the case of printed glass, uneven shrinkage during cooling could be problematic at best, and slow cooling in a kiln is the "usual" approach. Unfortunately, my electric kiln got its nichrome wire elements broken last time it was transported (about 35 years ago) and I never got around to fixing it.
