Chemical durability, specular gloss, and transmittance of optical glasses.

The chemical durability of three types of optical glass (BSC 517, BaC 572, and F 620) and chemical Pyrex llave been studied o\"er an extended pH range by means of an interfe rometer proced ure. The accompanying effect on the appearance (gloss retained) and on the transmittance of the specimens has also been determ ined. The results illustrate the con fu sion t ll at might a rise from choosin g any of the above th ree propert ies as an ind icator for th e serviceabil ity of optical glasses. Below pH 6, in the range of m ax imum durabil ity for t he optical glasses, differential solu tion of t he al kali and heavy l1'e tal ox ides brings about t he formati on of sili ca-ri ch, reflection-red ucing film s, wh ich decrease specu lar gloss of the surface and imp rove t he t ra nsmittance of the specimens .