Defect of the Month

June, 2022
Birdswing
While the air is filled with the sound of birds chirping this time of year and they are plentiful on the tree branches, a Birdswing is not a welcome sight in your glass. A Birdswing defect is a thin strand of glass stretched between two points on the inside surface of the container, sometimes referred to as a filament or in some part of the world a Monkeyswing. They generally occur in the body of the container, usually extending from side to side. They are caused when glass viscosity is too low and the opposite inside surfaces of the parison touch, causing them to fuse. During the final blow process, a filament will be drawn between the opposite inside surfaces. Birdswings or Monkeyswings are usually considered critical defects by most in the industry and pose a risk for breakage during filling or use with a potential for glass fragments in product.
January, 2022
View from the Top
This top-down image of a finish shows a thin line that extends radially across the sealing surface. These flaws are referred to as lineovers or “line over the finish.” Lineovers differ from split finishes in that they are only a surface flaw and do not penetrate into the glass; however, like split finishes, lineovers can cause sealing problems such as leakage, loss of carbonation, or spoiling.
December, 2021
Frosted Window Pane
As winter sets in over the northern hemisphere, brisk mornings reveal delicate frost crystals fanning across the windows on our houses and cars. The crystallized “porthole” seen in this polarized light micrograph is a close-up of a stone in a piece of flat glass. Telltale 60⁰ branching, along with other optical characteristics, identify the fernlike crystals as tridymite, a phase of silica (SiO2). Because silica (i.e. sand) is the primary component of most commercial glass compositions, tridymite stones can occur in food/beverage containers, tableware, and architectural glass.
November, 2021
Blue Worm
This wormlike flaw is actually classified as a type of stone resulting from AZS refractory erosion that drips into the melt. Typically AZS drip stones are composed of very small particles of zirconia that are embedded in nepheline and/or carnegeite. They are produced by decomposition of the AZS refractories in the superstructure or run-down of molten silica over AZS refractories. AZS stones should not be returned to the cullet stream as they are unlikely to melt in subsequent trips through the furnace.
October, 2021
Choked Neck
Choking is to be taken seriously, whether in people or glass bottles. Choked Necks are constrictions or obstructions in the bore of the neck. They usually appear below the neck parting line on the inside of the bore. There are different varieties of a choked neck or bore that in the majority of cases are the result of temperature issues in the finish region, the glass either staying too hot or too cold due the plunger’s inability to extract enough heat from the glass (glass too hot) or the plunger extracting too much heat from the glass (glass too cold). A choked or restricted bore can become a critical defect when the restriction is sufficient to cause contact with a fill pipe in the filling line, increasing the risk of glass contamination in product.