Defect of the Month

September, 2023
Crack Up
This typical lehr crack consists of fracturing in the bottom and sidewall sections of a wine bottle that was extended in the annealing lehr. Lehr cracks typically originate at moderately severe (or worse) flaws created upstream of the lehr. Most commonly, the flaw or damage is located on the bearing surface which then extends into a fracture due to the thermal stresses produced during the annealing process. A common feature of lehr cracks is a series of dwell marks on the fracture surface indicating that the fracture extended to a certain point and then paused before being acted upon again and extending further. Thick bottomed items such as sparkling wine bottles are more susceptible to lehr crack formation. Darker glass and thick bottoms can also lessen the likelihood that lehr cracks are identified through inspection. Lehr cracks are strength-reducing defects and may fracture the container immediately upon handling.
August, 2023
Cool Beans
If you’ve ever visited Chicago, it’s likely that you’ve seen it’s iconic, shiny “Bean” sculpture. Officially titled “Cloud Gate,” the smooth surface reflects the surrounding cityscape as well as the sky above. From a physics perspective, reflections occur when light encounters an interface between two materials with different refractive indices. The flaw in the photomicrograph causes a reflection due to the smooth interface air encapsulated within the glass. This type of flaw is an inclusion referred to as a seed or a blister, depending on its relative size. Seeds and blisters have a number of possible causes, ranging from problems with refining during glass melting to air that is entrapped during container formation.
July, 2023
Arctic Shoreline
Identifying contaminants in a glass container can be very challenging due to the sheer number of possibilities. Dirt, batch materials, lubricants, packaging, product residues, and organic matter can fall into or be deposited in a bottle during processing. Some contaminants occur relatively frequently, such as mold dope and iron oxide dust. Others can leave an analyst scratching his or her head as to how the substance could possibly have ended up in a container. This SEM micrograph shows a large salt crystal (NaCl) that formed due to evaporation of a liquid in the bottom of a bottle. The original source of the liquid could not be identified, but the lack of damage to the underlying glass indicates that the salty liquid was not introduced while the bottle was extremely hot during or soon after forming.
June, 2023
Weather Radar Map
This image bears a striking resemblance to a weather radar map. In reality it is an EDX spectral map conveys a huge amount of information by portraying each element in a particular color. The different areas are portions of a stone found in a glass container that have partially melted or recrystallized. This particular stone resulted in glassy areas (blue and yellow) that separated into calcium-rich and calcium-depleted phases. The red area is composed primarily of zirconia (ZrO2) and the green area is composed of alumina (Al2O3) with magnesia (MgO). The magnesium and zirconia are not found in the bulk glass composition, indicating that the stone likely originated from a refractory source.
May, 2023
Smoky Bones
It’s May, the official start of the summer grilling season when backyard grills will be fired up across America. This particular image of a stone in glass resembles a grilled chicken breast slathered in barbeque sauce – although maybe we’re just a little hungry. In any case, the colorful fringe around the stone consists of feathery nepheline crystals (Na2O·Al2O3·2SiO2), which were created by an aluminosilicate refractory stone dissolving in the surrounding glass. Aluminosilicate, or mullite, type refractories are most commonly used in the forehearths of container glass furnaces. The surface cracks around the stone are caused by high stresses due to differences in the coefficient of thermal expansion between glass and refractory materials.