This iron stone has reacted with the surrounding glass, creating a telltale greenish-brown swirl. Bottle caps and lids are a possible source of iron contamination in recycled cullet, but the use of magnetic separation usually prevents widespread problems from occurring. The internal cullet supply can be more vulnerable, however, and nuts, bolts, wire, or even mold parts have been known to find their way into the furnace.

Spring has arrived here in Western Pennsylvania and the birds are chirping and flying branch to branch. However, they cannot land on this “Birdswing” as it was found in the neck of a glass bottle. This critical glass defect is actually a thin strand of glass stretched between two points on the inside surface of a bottle. It is caused due to low viscosity of the glass, when the opposite inside surface touch, causing them to fuse. During the blowing out of the parison into the final shape a filament will be drawn between the points where the opposite inside surfaces made contact. The thin glass strand poses a risk for breakage during filling or use, which would create glass-in-product.

This month we are featuring a Scanning Electron Microscope (SEM) view of an open check/tear on the outside surface of a glass container. You would be excused, of course, if a quick glance led you believe this was an image of butterfly sitting on a mirrored surface.

While staring at this month’s unblinking defect might give you the chills, it actually is an alumina silicate stone within a viscous solution sack formed from a dissolving stone. It was found buried in the surface of a glass container and caused by a ceramic contaminant in the cullet stream.