Corrosion of Optical Glasses

After their manufacture from molten glass compositions, and before their being used, optical glasses are polished. In these polished glasses, three types of defects are possible. They are dimming, staining, and scratches. 

p is the refractive index, t is the thickness of fhe film, and n is an integer. 

The color of the stain is also dependent on p and t. Scratches tend to form on lenses during polishing. After polishing, the lenses are cleaned, and then they are examined. If there are scratches on them, such lenses are rejected. 

The composition of optical glasses has an effect on their durability. The main effect is from the type of network former that the glass contains. There are three main glass network formers—silicon, boron, and phosphorus. 

Silicon is fhe network former in silicate glasses. Silicate glasses are the most common optical glasses. These glasses are resistant to water at ordinary temperatures. Except hydrofluoric and phosphoric acids, other acids do not attack these glasses. However, alkaline solutions do attack them. 

---