MODERN GLASS — STOOKEY 329 



colleagues and I soon found that the principle of nucleation-con- 

 trolled crystallization of glass can be very broadly applied. Plate 3 

 shows three stages in the process of nucleation and crystallization in a 

 glass ceramic. 



Meanwhile, a search for materials suitable as radomes for super- 

 sonic missiles made for the Navy by the Jolins Plopkins Applied 

 Physics Laboratory, singled out some of the new glass-ceramics as 

 being almost unique in meeting the requirements of strength, resist- 

 ance to supersonic rain erosion and thermal shock, and radar- trans- 

 mitting properties. This led to pilot production and testing of 

 radomes for the Terrier and Tartar missiles now standard on the 

 missile ships of the Navy. Use of new glass manufacturing methods, 

 developed in continuous-tank production of optical glass, resulted in 

 radomes that can be mass-produced uniformly and not individually 

 tailored to meet the boresight tolerances required for accurate aiming 

 of the missile. One of these is illustrated in plate 1. More and more 

 varieties of radomes, ultrahigh- frequency windows, and antennas are 

 being made of glass-ceramics. 



The strength, chemical resistance, and thermal shock resistance of 

 some of the low-expansion glass-ceramics suggested that they could 

 be valuable for domestic use as well as for defense ; and we developed 

 the now-popular heat-resistant ceramic utensils for cooking and serv- 

 ing food. A new high-strength glass-ceramic tableware will soon be 

 commercial. 



Still newer glass-ceramics are now in the development stage, each 

 tailor-made for a special area of use. One, having exceptionally high 

 dielectric constant, is being developed for capacitors; another, con- 

 taining crystals of an electronic semiconducting oxide, will be used 

 for high-temperature resistors. And a third variety of glass-ceramics, 

 higlily crystalline, contains crystals so small that they do not scatter 

 light, and this glass-ceramic is as transparent as glass. The crystals 

 are beta-eucryptite, a strange mineral which shrinks, instead of ex- 

 panding as do most crystals, when heated. The resultant glass- 

 ceramic has a negative coefficient of expansion. 



STRONGER GLASSES WITH CRYSTALLINE ARMOR 



The latest chapter in this story will be found in a paper presented 

 by my colleagues and myself at the International Glass Congress in 

 Washington, D.C. This paper describes two methods, still in labora- 

 tory stage, of producing glass armored by a transparent skin of the 

 negative-expansion eucryptic glass-ceramic. This armored glass has 



