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Defect of the Month

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Filter Dust
Dust Bowl
February, 2024

Have you ever wondered what was in the dust sucked up by your vacuum cleaner?  At a glass plant, the profusion of compressed air lines, exhaust ducts, and cooling air means that there is a lot of air in circulation, all of which can contribute to a dusty environment. Filters are used to minimize the dustiness, and those filters sometimes become clogged. This EDX composition map shows the contents of one such filter. In an optical microscope, the dust looks like dirty sand, but the spectral map easily discerns between glass fragments, limestone, and soda ash. All three are batch materials used for making glass. The small amount of chlorine is due to salt.

Stone in glass
Bleached Nugget
January, 2024

Here in the United States, the fast food chain Chick-fil-A is renowned for their delectable fried chicken offerings. With just the right amount of crispy breading, their chicken nuggets are perfect for dipping into a variety of sauces, including the author’s favorite –Polynesian. This image of a stone in glass resembles a (rather bleached) nugget at the precise moment before being dunked into a (rather colorful) sauce.  The “crispy breading” is comprised of small nodules of zirconia (ZrO2), which were created by the interaction of the glass melt with an AZS refractory. The glassy phase of the refractory dissolves over time, creating an alumina-rich solution sac and a stone of nodular zirconia. The “sauce” in this image is the induced stress in the surrounding glass, rendered visible with polarized light. 

Thin Ice Point Contact
Thin Ice
December, 2023

When a hard, pointed object smashes into a glass surface, it’s a bit like an ice pick biting into a frozen pond. Pronounced ripple markings extend downward from the impact site, while crushed glass marks the origin of the damage on the surface. Point contact damage is a sign of rough handling, and can be caused by glass fragments from a prior breakage event or exposed metal points somewhere in the factory. Lastly, the blue color in this image is not the actual glass color, but is just a reflection from an object used to enhance visibility of the surface markings.

Bright Stripe
Bright Stripe
November, 2023

Stones and cord in glass can sometimes go hand-in-hand. This container has a large refractory stone in the heel that also created a highly stressed cord in the sidewall. Although a polarimeter cannot reliably detect cord when the bottle is viewed through the sidewall, high magnitude cord stress can sometimes be seen in this manner. The small knots of stress within the cord are additional particles of the stone created as it dissolved within the melt.