Super scratch resistant

[Rich R]

Anyone have opinions good or bad about the extra scratch resistant lenses in cr 39 and polycarb, are they really much better than the regular scratch resistant lenses and do you encounter any problems during surfacing or finishing processes
Rich R

[JERRY HUANG]

Standard CR-39 = #4 pencil hardness
Standard polycarbonate = #3 pencial hardness

Add hard coating:
Cr-39 = #8 pencil hardness
Polycarbonate = #6 hardness

Hard coating can be grind away if applied before surfacing.

[bwheeler]

I believe that super hard coatings do perform better than the standard scratch coatings but I don't know of one that is tintable
at this time. Whenever a customer asks me if they can be scratched, I will tell them that anything can be scratched and the threshold of scratch resistance cannot be measured in the practice of wearing the lenses.

[JERRY HUANG]

Sure! The hard coating is just a layer (or layers) of hardner and it is tintable. If not, the problem must be from the lens itself.

[Jim G]

So far, the "law" reads: The more tintable; the less scratch resistant. And, visa-versa. Therefore, the more S/R coatings are less (not?) tintable.

The industry has struggled trying to develop a test to measure scratch resistance but with little luck. The AO test, tumbling the lenses in a mixed media drum, has been "advertised" as having some consumer wear corrolation but, we didn't find it very consistant nor repeatable. Possibly the most widely used is the "Bayer" test where a lens is placed in a pan with a known abrasive (like sand) and oscillated back and forth. The "eraser" test (noted above) and Tabor (used in industry) are also commonly used.

If you were to get your hands on a partially coated lens and abrade the surface with, say, steel wool, you'd note a dramatic difference in scratching tho, as bwheeler noted, you'd still get a few scratches.

Lastly, as Jerry noted, if one was to put the same hardcoat on different lens substrates, you generally do see a difference in scratch resistance...if we knew how to measure it, that is.