Optical glasses exhibit very different properties during manufacturing process. Densification of glass under pure
pressure dramatically changes the material removal mechanism. In glasses with densification, the densification inhibits
the propagation of subsurface damage but also masks subsurface damage. Densification is the primary form of
subsurface damage at ductile removal mode, like polishing, when material can be densified with pure pressure.
John C. Lambropoulos,
"Densification contributions in material removal mechanism", Proc. SPIE 10316, Optifab 2007: Technical Digest, 103160A (14 May 2007); doi: 10.1117/12.717996; https://doi.org/10.1117/12.717996