The two semi-circular “owl eyes” in this microscope image are actually dwell marks on the bearing surface of a bottle. The dwell marks reveal the initial depth of bearing surface checks on adjacent knurls. Residues of iron on top of the knurls indicated that the checks were created by forceful contact of the hot bottle with an iron object – possibly the “dead plate” – soon after bottle formation. The checks weakened the bottle, causing it to fracture during quality control testing.

The tapered tail in this polarized light microscope image is a stone inclusion in glass created by erosion of an AZS refractory. The drip from a refractory is more viscous than the bulk glass, and can be twisted and distorted into whimsical shapes. Due to its source, the composition of the tail is enriched in alumina and zirconia relative to the surrounding glass. The fine branching lines seen within the tail are recrystallized nepheline, which is a type of stone with the formula Na2O·Al2O3·2SiO2.

A large crystal of Beta-wollastonite (CaSiO3) takes on a vibrant array of rainbow hues in this polarized light microscope image. Like other devitrification stones, wollastonite crystals are produced when the temperature of the glass melt drops below the liquidus point for a prolonged period of time. In particular, wollastonite crystals tend to form in the coolest spots of the forehearth, such as around the orifice ring. The formation of the crystals shown here was also promoted by a batch enriched with calcium.

This is a crystal shown at 100X magnification and is from a ‘Silica Frost’ stone. The crystal structure confirms the presence of the tridymite phase of silica. The stone typically results from a drip from a silica crown refractory material falling into the molten glass batch.