Sapphire lapping film uses fixed diamond abrasive particles bonded to a polyester backing for precision flattening of watch glass blanks.
Polishing pads made of polyurethane foam apply the final mirror finish with colloidal silica slurry.
Choosing the right film grit sequence from 15 micron down to 0.5 micron determines surface roughness measured in nanometers.
The pad hardness and slurry flow rate must be tuned to avoid edge rounding on sapphire crystals.