Blocking pad marks on CR-39 lenses?

[tdj]

I had 3 pair of lenses come back yesterday. All 3 were FT-28 CR-39, two were hard coated, one was not. No A/R. Anyway...

so the lenses checked out fine, no visible distortions, scratches, or marks in the lenses. UNTIL I sprayed to clean... and all 3, both lenses, had a very visible blocking pad mark! Again, no visible distortions or anything until sprayed. It wasn't residue -- tried getting it off with alcohol, no go.

What on earth is going on there? Something wrong with their edger or the person running it? What would cause that? I called and they said send them back and they would look into it, so I did, but I don't know much about the lab side of things, so I'm curious as to what would cause this. Thanks!

[CME4SPECS]

probably too much pressure on the chuck. Put the lenses in the salt pan for 30 seconds or so and they will disappear

[tdj]

probably too much pressure on the chuck. Put the lenses in the salt pan for 30 seconds or so and they will disappear

Oooh, already sent 'em back, but if it happens again I'll know what to try!

[uncut]

Now remember, class(for those of you taking notes, and are students, or a reasonable facsimile, thereof)....do not try this at home, unless you first are confident that:

1) the lenses are removed from the frame.
2) your and/or your firm are willing to cough up for toasted lenses, if something goes wrong.
3) the lenses in question are neither polarized or harbour surface treatments that can be heat damaged.

[PRECISIONLAB]

I agree with earlier posts..chuck pressure or an over agressive blocking pad. I would avoid salt pan..you may go from marks to blisters or crazing with ar lenses. Hopefully your lab will address this issue. If not, a warm water bath..extra pot in tint unit should "relax" marks on lenses.

[Chris Ryser]

Glue marks from pads..............you are right some heat will make them go away

[mdeimler]

If not, a warm water bath..extra pot in tint unit should "relax" marks on lenses.

That's exactly how to relax the pressure areas from the chuck. I used to see it more on Transitions.

[King of the Lab]

Type of blocking pad. (some are far stickier than others)
Chuck pressure inside machine. (usually adjustable)

[njeyedr]

I once was told to let them sit in boiling water. It works 80% of the time.

[mdeimler]

I once was told to let them sit in boiling water. It works 80% of the time.

Actually, boiling is a lil hot. 160-180 is the best temp range that we've found. Yes, we did the double blind study research