04/07/2026
https://www.insulators.info/general/glassfaq.htm
This excellent historical glass manufacturing information is focused on insulators, but also applies to what we see in the jar collecting hobby. Enjoy!
What we call 'underpours' are hardly ever caused by an insufficient volume of glass in the mold. They are usually caused because the glass cools before it can be squeezed into the small areas of the mold. This is why underpours occur on the base and inner skirt region. This is the area where there i...