Originally Posted by
sharpstick777
If the lens has an oliophobic top coat, crazing is far more often due to internal issues with the hard coat, and much less with chemical exposure, as the chemicals must enter through the top coat.
The exception is around the edges, if crazing is only or more around the edge then its more likely a chemical exposure or a lens edged oversize. This can happen with spin coats not laying out evenly as well.
If its in the center only, its often caused by the lens being surfaced too thin. Lenses have to a certain thickness for good heat dissipation in degassing. (degassing is baking a lens to get rid of water content). This can be exaggerated by blocking, when the lens goes under pressure in the edger it weakens the HC if the material is too thin. An edger with too much chuck pressure can also contribute, but that is rare in a lab, more common in practices that edge though.
If its across the whole lens, heat/cold or a poor coating is the likely culprit.
Some lenses also require a primer coat, and if that is skipped it can lead to crazing.
Often lenses are not crazed when the leave the lab, but the defect shows up a day, a month or a year later.