Defect of the Month

August, 2017
Tricky Trilobite
Is this a fossil of a prehistoric trilobite or another glass defect? You’d be correct if you guessed the latter! This microscope image is of a defect called a “bump check.” Bump checks are caused by momentary, glancing contact between containers, producing a characteristic pattern of opposing crescent cracks. Bump checks that occur soon after container formation have tell-tale signs of hot-end contact, such as small pieces of missing or adhered glass.
July, 2017
Cassini Flyby
The Cassini-Huygens space probe has been orbiting Saturn since 2004, producing many spectacular images of the planet’s moons and rings. In spite of its resemblance to the latter, this image is not one of them! Instead, the “rings” shown here are actually streaks of cord in a sample of container glass. The cord streaks have a slightly different composition than the surrounding glass, inducing stresses that can be visualized with polarized light. These stresses are permanently locked into the glass, and can combine with other stresses to cause breakage at lower loads than would otherwise be expected.
June, 2017
Klingon Warship
A Klingon Warship or a Y-wing Starfighter? When imaged with a Scanning Electron Microscope (SEM), this stone is evocative of spacecraft from popular science fiction franchises. In reality, the vaguely menacing profile was created by slicing a partially-formed hexagonal crystal at an oblique angle. Although SEM images themselves are black-and-white, colors can be assigned to different elements in a spectroscopic method called “compositional mapping.” These colors reveal that the stone was created by an AZS refractory that recrystallized into prisms of nepheline. Our new SEM makes it possible to routinely use compositional mapping to help identify stones. If you have stones in your glass, send them in to AGR via ground, air, or space for analysis.
May, 2017
Tarantula
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.