tempering glass by quenching almost molten glass in a heated bath of oil or grease in 1874, the method patented in England on August 12, 1874, patent number 2783. Tempered glass is sometimes known as Bastie glass after de la Bastie. In 1877 the German Friedrich Siemens developed a different process, sometimes called compressed glass or Siemens glass, producing a tempered glass stronger than the Bastie process by pressing the glass in cool molds. The first patent on a whole process to make tempered glass was held by chemist Rudolph A. Seiden who was born in 1900 in Austria and emigrated to the United States in 1935. Though the underlying mechanism was not known at the time, the effects of "tempering" glass have been known for centuries. In about 1660, Prince Rupert of the Rhine brought the discovery of what are now known as "Prince Rupert's Drops" to the attention of King Charles II. These are teardrop-shaped bits of glass which are produced by allowing a molten drop of glass to fall into a bucket of water, thereby rapidly cooling it. They can withstand a blow from a hammer on the bulbous end without breaking, but the drops will disintegrate explosively into powder if the tail end is even slightly damaged. See also Thermal stress Borosilicate glass Fire glass Superglass Low-iron glass Stained glass Lead glass References Glass engineering and science Glass types Glass physics pl:Hartowanie#Hartowanie szkła