"Despite its initial success, Pyrex sales began slowing down in the 1920s. Pyrex was a borosilicate glass, expensive to manufacture due to its higher melting temperatures, and, as a result, priced more as a luxury purchase, not easily affordable by the masses. It wasn’t until Corning developed an automated production process in the 1930s that prices on Pyrex dropped and sales were able to rebound."
Pyrex Flameware Six-Cup Percolator, made by Corning Glass Works, 1939-1951.