Defect of the Month

October, 2020
Flying Bug
This summer in Western Pennsylvania we have had to contend with mosquitos, flies, bees, hornets, and now these flying bugs. The bug-like inclusion shown here is a common crystalline devitrification stone called Beta Wollastonite. Wollastonite is composed of calcium silicate and will form in cooler areas of the furnace and forehearth. It typically crystallizes into large prisms that produce vivid retardation colors in polarized light. These types of stones will not melt in molten glass and thus the cullet containing these stones should not be re-introduced into the batch.
May, 2020
Blossoming Flower
This blossoming flower is actually crystalline calcium carbonate (Ca2O3) that has grown on the inside surface of a bottle. This crystal was the result of atmospheric weathering present on the surface and is somewhat unusual in size as compared to others on this bottle and what is normally identified as small hexagonal crystallites. The picture was taken at 2500 X and colorized according to elemental composition.
April, 2020
Hollow ACL Inclusions
Applied Ceramic Labels (ACL) are permanently bonded to glass containers by screen-printing a mixture of glassy material, pigment, and organic binder, then firing the container in a decorating lehr. The resultant label is highly wear and chemical resistant; however, defects such as this void can lower the surface strength of the glass container. Inclusions can also be caused by insufficient fusing temperatures, application issues, or raw material contamination. Because ACL is opaque and rather thin, light microscopy is of limited usefulness in finding these flaws. Consequently, SEM-EDX is the preferred imaging technique.
March, 2020
These gaseous inclusions are called seeds but also are known as blisters or bubbles. The term “blister is often used for larger seeds. Seeds have many possible causes, including but not limited to inadequate refining, problems with the glass chemistry, reboil, contaminants, or by mechanical trapping of air during bottle formation. Depending on their location and type of seed, they can be considered critical defects or non-critical yet strength-reducing. Seeds at the inside knuckle lower the resistance of the container to internal pressure and thermal shock loads. Seeds on the inside surface at the contact points can reduce the resistance of the container to impact loads.
February, 2020
Winter Weathering
We took artistic license in transforming this Scanning Electron Microscope image into a snowy winter scene. The green “branches” are crystals of sodium carbonate (Na2CO3), the white “snowflakes” are hexagonal crystals of calcium carbonate (CaCO3), and the blue “sky” is the inside surface of a glass bottle. These crystals are created by a process referred to as weathering, where moisture and carbon dioxide in the air react with an uncoated glass surface. If severe enough, weathering can cause bottles to have a cloudy white appearance, not unlike a frost-covered window.