Professor Uhlmann's chemically tempered glass demonstration

Tom's teacher (D. R. Uhlmann; cluster name in aggregate uses captioner mishearing "Omen") demonstrated chemically tempered glass by hand-flattening a curved 18″ × 3″ piece without breaking it. The pedagogical demonstration of ion-exchange surface compression.

Professor Uhlmann, who taught me, who was a glass expert, had a piece of glass that was about 18 inches long, three or four inches wide, and was bowed about two inches high. He could take that with his bare hand and just flatten it, just like that, and it wouldn't shatter, wouldn't break, even with that type of curvature. When he flattened it, he wasn't exceeding the compressive residual stresses that he got by putting sodium and potassium ions replacing the lithium ions. Fairly expensive, because that one piece of glass has to sit in this furnace for several days to diffuse in this ion exchange. In fact the John Hancock building has chemically tempered glass of sodium and potassium.