Defect of the Month

October, 2017
Galileo’s Saturn
In 1610, Galileo became the first person to observe the rings of Saturn. His small, home-made telescope made it difficult to fully resolve the rings and consequently some of his drawings showed ambiguous lobes extending from a central sphere. Today, we have high resolution optics that allow us to magnify small nearby objects, such as inclusions in glass. This copper stone, with its brownish extensions, resembles Galileo’s early Saturn drawings. Copper stones in glass are caused by cullet contaminated with copper wire or coins.
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.