Defect of the Month

May, 2017
While this defect in glass shows a striking resemblance to a tarantula it is actually Sodium Carbonate Crystals caused by atmospheric weathering on the inside surface. When combined with a carbonated liquid, foaming can result. This image was captured on the AGR Scanning Electron Microscope (SEM) at 430 X magnification.
April, 2017
Ball on the Green
Most non-metallic stones are irregular chunks or globs. That’s why this golf ball-shaped stone is so unusual and hints at an uncommon origin. When the composition was analyzed, it was found to be made of an AZS refractory-like material, but the internal structure was spherical – completely unlike any furnace refractory. This stone was almost certainly a ceramic grinding or polishing bead, commonly used for machining operations. It probably entered the glass batch as a contaminant in the cullet or from the mold machining process.
March, 2017
Crystal Tribble Troubles
When allowed to cool at a slow rate, molten glass can crystallize into minerals in a process known as devitrification. In most cases, devitrification is a problem for glass furnaces because it is a sign of cool spots or inadequate mixing. There are two devitrification products in this polarized light micrograph: the globules are composed of cristobalite (SiO2), while the fuzzy fringe is composed of devitrite (Na2O·3CaO·6SiO2). Tribbles, of course, are the cute but prolific alien creatures from Star Trek. The balls of cristobalite dendrites scattered across this sample resemble tribbles’ hairy, spherical bodies.
February, 2017
These long columnar crystals are composed of manmade vanadium oxide (V2O5) crystals, known as Shcherbinaite when found in nature. While not technically a defect itself, this particular sample is used as a standard for quantitative analysis of vanadium-containing metals. Almost any trip to the hardware store can uncover a plethora of chrome vanadium hand tools, such as hammers, wrenches, or knives. Glass products can be damaged by similar metallic objects, leaving behind residues on the glass surface. Using standards like this one, we can match the composition of the residue to a particular alloy or the suspected metal object itself.
January, 2017
Tridymite Triggerfish
This “fish-faced” stone is actually a conglomerate of very small quartz grains that are being converted into laths of tridymite. The uniform size of the grains and the large tridymite laths suggest that the stone originated from a silica refractory, most commonly found in the crown of a furnace. When viewed in polarized light, the different minerals take on vibrant rainbow hues. The overall shape bears an uncanny resemblance to the Clown Triggerfish, an animal found swimming among coral reefs in the Indian Ocean.