Defect of the Month

January, 2019
This “snowflake” is actually a crystalline inclusion embedded in solid glass as viewed through a microscope. When a silica rich area of the glass melt cools below the liquidus temperature, crystals of tridymite (SiO2) such as those shown here can form. Tridymite crystals can also form in the vicinity of a silica batch stone.
December, 2018
This crystal formation of atmospheric weathering is composed of calcium and sodium carbonates on the inside surface of a glass container. This unusual weathering formation has the appearance, when colorized on our scanning electron microscope, of a holiday wreath.
November, 2018
Diatomaceous earth
Diatomaceous earth–is a naturally occurring, soft, siliceous sedimentary rock that consists of fossilized remains of diatoms. Diatomaceous earth is a thermal insulator and primarily composed of silica and is sometimes used as a refractory packing material in the glass industry. This is an unused sample that was analyzed to compare physical and compositional properties to a stone analysis.
October, 2018
Point Contact
This photograph shows a fracture origin at point contact damage on the knurling of a bottle. As the name suggests, point contact damage is caused by forceful contact with a hard, pointed object. The culprit is often a shard of broken glass or protruding metal on a conveyer or transfer area. This particular bottle failed during internal pressure testing, causing the bottle to fracture across the bottom surface.
September, 2018
While this defect is similar in appearance to the little insect called a silverfish it is actually a stone (i.e. solid inclusion) in the glass composed of molybdenum oxide, sodium molybdate, or calcium molybdate. With a high melting point of 2623°C, molybdenum is commonly used as an electrode material for supplying additional heat in container glass furnaces. When the electrodes degrade or are exposed to air, they can create “silverfish” shaped stones in the glass.