Fractures in the bricks sometimes become shifted and lifted out of position by the slowly dissolving ever-widening cracks. The expansion caused by the off-gassing of dissolving materials actually lifts and floats these pieces slowly toward and sometimes into the glass tank.

Liquid glass is extremely corrosive. The chemical activity, aided by the extreme temperature, slowly dissolves the furnace and everything it's made of. Zirconia furnace bricks last about 5 years of continuous use, but I can't really afford them, so I go with a cheaper alumina composition that gives me around 400 hot days of use. 400 days of use lasts me 6-7 years and melts me around 80,000 pounds of glass. As the furnace nears the end of it's useful life, erosion starts to get worse and the eroded materials find their way into the glass tank. Here is a series of 6 pictures that show some of this erosion and how it played a role in old insulator production.