A wedge-shaped dwell mark is shown in this top-down image at the fractured shoulder of a pharmaceutical vial. In this case, the dwell mark indicates the existence of a check prior to the fracture of the shoulder. Metal smears along the seam show that the check was created by abnormal contact between the container and the blow mold. Although the check did not cause a critical defect (i.e. leaking product or glass in product), it would have lowered the strength of the vial. The check was intentionally broken open in our laboratory to expose it for analysis.

This Dendritic Zirconia Crystal is clearly visible when viewed in a polarizing microscope at a magnification of 50X. The enhanced clarity is achieved through the composite layering of 14 separate photos that are stitched together to provide sharpness, depth and detail to the image. The stone itself results when the surface of an AZS refractory melts sufficiently to allow a drip to form and fall into the glass melt.

This is an unusual sample of the tails of cord associated with AZS refractory drip. This tail is one side of a large glassy knot with six sided dendritic zirconia crystals and a hazy mist of nepheline. Tails usually appear on both sides of the glass knot.

The colorful swirls in this microscope image are actually subtle differences in glass composition known as cord. Batching errors, refractory erosion, or insufficient mixing can create streaks or bands of glass in containers with a different compositions than the bulk. Because the composition of the cord differs from the rest of the glass, so too does the coefficient of thermal expansion. When the glass cools, these differences create permanent stresses on the container that can lead to premature failure. Polarized light reveals the stresses in the glass caused by the cord, which can be measured using special microscopic tools and procedures.