Defect of the Month

May, 2021
Unfilled Finish
Have you ever started a home-improvement project, but stopped because you ran out of materials? The defect in this picture is a little bit like a partially completed project and is referred to as an ‘unfilled finish.’ It occurs when the glass weight is too low and there isn’t enough glass left to fully form the finish. This type of defect prevents the bottle from being capped.
April, 2021
Butterflies in the sun
The picture was taken at 100x magnification in a polarizing microscope with a first order red insert. This is a stone that exhibits bright birefringence with crystals of zirconia at angles that are reminiscent of butterflies in flight. The stone is a melted viscous layer of a AZS refractory that dropped into the molten glass from above the flux line. Once surrounded by the molten glass it experienced comparatively cooler temperatures and the droplet recrystallized to form six sided crystals. The melting of AZS refractory that led to the stone creation had been caused by batch dusting and/or misdirected burners causing spikes in furnace temperature.
March, 2021
Egyptian necklace
Traditional necklaces of ancient Egypt incorporated parallel rows of beads, creating heavy concentric bands around the wearer’s neck. This image of a fracture origin presents a similar effect. Pronounced ripple markings on the fracture surface, such as those on this sample, are a hallmark of point contact damage. As the name suggests, point contact damage is caused by forceful contact with a hard, pointed object. This particular origin was found on the sealing surface of a bottle, and analysis via SEM-EDX revealed glass-to-glass damage nearby.
February, 2021
Evergreen Forest
While this images evokes an evergreen tree line along a cliff’s edge, the photograph is actually an example of the oxide of zirconium (zirconia), which has melted and re-crystallized to form a stone in a glass container. Zirconia is a key component in a variety of high temperature refractory materials. Typically, these crystals are created through viscous flow of the surface layer of an AZS (alumina, zirconia, silica) refractory located above the flux line in the glass tank. When the melted AZS flows into the molten glass bath, it is actually cooled and recrystallizes into the structures depicted in the photograph. The image was captured with a polarizing microscope at 100 X magnification and with a first order red tint plate in place.
January, 2021
Sea Creatures
The objects in this image resemble a cross between waffle fries and red blood cells, but are actually the silica skeletons of microscopic sea creatures called diatoms. You may be familiar with diatoms as an ingredient in toothpaste or for killing garden pests. But these useful remnants of marine life are also found in glass plants as a furnace insulation material and an oil absorbent. This particular SEM micrograph was taken from a stone composed of diatoms that was pressed into the outside surface of a glass container.