Defect of the Month

May, 2018
Puzzling, isn't it?
Gaseous inclusions of various shapes and sizes can occasionally be found in container glass. The gas inclusions are often designated as seeds or blisters, depending on their size. These gaseous inclusions can originate from different sources however they are all formed at melting temperatures ( > 1100oC), when glass is in the liquid state. The surface tension of the molten glass results in a spherical shaped bubble in the glass melt. During forming, the gaseous inclusion can assume either a round, oval or elongated shape depending on its location and the glass flow during the forming process. In this example, it appears as though the gaseous inclusion(s) could ‘fit’ together like puzzle pieces to once again form an oval shaped blister.
April, 2018
Cosmic Jelly Bean
Jelly beans are especially popular this time of year, although the kidney-shaped confections from our galaxy don’t have the neon blue color of this very small stone. In fact, polarized light microscopy is responsible for the vibrant hues of this otherwise colorless crystalline grain. The tiny pores within the grain itself are characteristic of a manmade material known as tabular alumina (Al2O3). This form of alumina is used in many types of refractories, which most likely accounts for the origin of this stone.
March, 2018
A Bottle’s Worst Nightmare
Silicon balls can be a bottle’s worst nightmare. This type of stone is caused by aluminum contamination in the cullet. When the aluminum reacts with molten glass (mostly silicon dioxide), it exchanges places to create aluminum oxide and elemental silicon. Because silicon has a lower coefficient of thermal expansion than glass, these stones exert a very high stress on the surrounding matrix after the glass cools. They severely weaken the container and can cause it to break due to relatively mild loads later in the filling process. This SEM micrograph shows a damaged silicon ball (often they are found in a perfect spherical condition) that was found at a fracture origin.
February, 2018
Temple Ruins
Looming like the weathered ruins of an Egyptian Temple, this crystal of calcite (CaCO3) rises out of a roughened desert of corroded glass. It is well known that some liquors can attack the inside surfaces of glass containers by leaching sodium and calcium out of the glass. The leached glass is vulnerable to corrosion or delamination, leading to the roughened surface seen in this SEM image. The calcite crystal possibly grew on the roughened surface due to the increased concentration of calcium in the product after leaching.
January, 2018
Damascus Dagger
Damascus steel blades are known for their extreme resilience and swirling two-toned bands. The method by which historical Damascus steel was produced is hotly debated, but high-quality knives made via a similar process are still available for the discerning aficionado. The banded inclusion draped over the finish of this container is also made of iron, but unlike Damascus steel, it would not make a very good sword. Most of the metal has reacted with sulfur in the glass melt to create iron sulfide. The iron sulfide blister was then elongated during the forming process into the blade-like inclusion shown here.