ABSTRACT
This chapter will discuss a much different approach to photosensitive processes in glass, or perhaps the more appropriate word would be "on" glass, since it will be more of a surface reaction. The glass we will describe is a unique one that has been around for over 80 years.1 What makes it a somewhat interesting story is that it is a glass produced in an intermediate stage to the intended product; namely, a high 97% silica glass melted in a conventional glass-making manner. High silica glass, like fused silica, is formed by a vapor deposition process and not by conventional melting because the melting temperature is > 1800°C. The unique invention1,2 was to melt an alkali borosilicate glass and then take advantage of a known effect in certain glass composition systems, which is the thermodynamic phenomenon of phase separation.
