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Thread: Why do lenses craze?

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    Why do lenses craze?

    Client picked up her glasses three days a go and she came back because one of the lenses were crazed, it was replaced and than she came back again because the other one got crazed when it wasn't before, strange.

    What are the reasons they craze? Bad batch? Should I ask her what she does for a living? I know sometimes if the lens is inserted to tight it can happen but she's definitely doing something to craze them.

    I was thinking of giving her a easy clean coating.

    What do you guys think it can be?

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    whats she cleaning them with? i had a guy who cleaned his with alcohol every day and that happened.
    "what i need is a strong drink and a peer group." ... Douglas Adams - Hitchikers Guide to the Galaxy

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    I clean mine everyday with alcohol. .. :-)

    Heat is usually a factor. The plastic expands and the ar don't ... or I had a high minus in a flexible optyl frame... the center was so thin the lenses easily folded in this particular frame it they kept crazing. We ended up switching frames and was no longer an issue.

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    Quote Originally Posted by Slim View Post
    I clean mine everyday with alcohol. .. :-)

    Heat is usually a factor. The plastic expands and the ar don't ... or I had a high minus in a flexible optyl frame... the center was so thin the lenses easily folded in this particular frame it they kept crazing. We ended up switching frames and was no longer an issue.
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    "what i need is a strong drink and a peer group." ... Douglas Adams - Hitchikers Guide to the Galaxy

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    ABOM Wes's Avatar
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    What does the crazing look like? Is it everywhere or centrally located and shaped like a block? Are the cracks vertical, horizontal, circular, or sporadic? What's the shape of the frame? What's the RX?
    Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA

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    Crazing in my experience is down to heat. The best way to craze a lens quickly is to pop it into a frame heater.

    The best way for a patient to do it could be very hot air (hairdryer - I've seen that before, but it's not common) or they could have been left in direct sunlight in a hot environment. A car is a perfect environment for this, as it works like a greenhouse almost.

    Ask her - what have you got to lose? You've already wasted two pairs of lenses, what if you have to do this every week for six months??

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    I had a patient with crazed lenses. I told her it looked to me like she was cleaning it with chemicals (such as windex). She told me I was crazy... she only uses the lens cleaner we sell...except when she uses her husband's denture cleaner on them. Uh what?

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    As far as heat goes, sometimes a good blast from an oven door just opened (although rare). Steam room or Sauna also is a possibility. Wes has a good question- if the crazing is just in the center of the lenses, it could have been from edging or a strong thumb pushing on the lens to mount. Is the crazing more of the thin lines (like a spider web) or more of a wavy smudging throughout the lens? And if the lenses are too tight, that will make the lenses more susceptible and likely to craze. And cleaning them with alcohol for only a couple of days shouldn't have caused this. Unless the a/r was bad to begin with.

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    denture cleaner on them that a new one

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    Temperature will cause the lens coating to expand and contract. If the hard coat on the lens is uneven (as is often the case with back-side spin coating), it will expand unevenly. The uneven expansion under the AR stresses the AR coating, and causes it to crack/craze.


    This is why 'high end' AR coatings use a dip coat. The dip coat can be controlled and applied much more evenly than a spin coat, and they tend to have fewer problems with cracking and crazing.


    Since a spin coat thickness can vary from one lens to another, this could be why one lens would craze and one would be fine.


    Did she maybe just leave them on the dashboard of her car?
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    +1!

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    Blue Jumper What does the crazing look like? ................................

    Quote Originally Posted by Wes View Post

    What does the crazing look like? Is it everywhere or centrally located and shaped like a block? Are the cracks vertical, horizontal, circular, or sporadic? What's the shape of the frame? What's the RX?

    Wes has given you the proper answer. Without knowing how the crazing looks like how can you get proper answer to you question.

    You will only get a guessing game.

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    Chemical, heat, compatible AR

    AR may craze due to:
    Exposure to heat
    Exposed to acetone based products
    AR coat incompatible with lens material (especially high index)

    • aBBerated

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    Crazing can also happen because of a contaminated coating, too much water in the air line, the coating is old or other errors.

    A great hard coat is not necessarily the hardest, but one that expands at the exact same rate as the base material. The harder the coating the great its possibility of crazing.

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    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.
    Last edited by sharpstick777; 07-29-2014 at 11:27 AM.

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    Heat is the problem, almost always! Hot water from the faucet has crazed a few lenses lately. I figured that out by grilling a customer who wears their glasses all the time. Have the been left in the car? no. Checked in luggage? no. Wore them in a sauna? No. Any reason at all you can think they would have got hot? Well hmmmmm. I do clean them every day under hot water. What? I let the water get as hot as possible and then clean them. Yeah don't do that anymore. Cool water. Never hot. I even had a guy boil his glasses thinking that would help clean them.... Face palm

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    Quote Originally Posted by becc971 View Post
    whats she cleaning them with? i had a guy who cleaned his with alcohol every day and that happened.
    We use alcohol every day to clean the lenses; it works great and does not effect coatings. We us the strong stuff as the weak does not work. The lab cleans the lenses with alcohol as well; it is not bad for coatings.

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    Quote Originally Posted by globaljp View Post
    Heat is the problem, almost always! Hot water from the faucet has crazed a few lenses lately. I figured that out by grilling a customer who wears their glasses all the time. Have the been left in the car? no. Checked in luggage? no. Wore them in a sauna? No. Any reason at all you can think they would have got hot? Well hmmmmm. I do clean them every day under hot water. What? I let the water get as hot as possible and then clean them. Yeah don't do that anymore. Cool water. Never hot. I even had a guy boil his glasses thinking that would help clean them.... Face palm
    Crazing after a lens is older than a month is almost always a heat issue. We get them in Florida and I did it myself to a pair but we find the most problems with transitions; it is not even close.
    We replace at 1/2 off after one year but before year two and at n/c in first year one time.

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    Thank you for all the responses.

    It's a slightly curved frame and she's not doing anything extraordinary with it in terms of cleaning or leaving it exposed in the sun, crazing seems to be in the middle. I have her a easy clean lens, let's see if that fixes the issue.

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    Quote Originally Posted by Craig View Post
    We use alcohol every day to clean the lenses; it works great and does not effect coatings. We us the strong stuff as the weak does not work. The lab cleans the lenses with alcohol as well; it is not bad for coatings.
    Craig, using pure undiluted Isopropyl to clean lenses 2 to 3 times a day will wear down coating MUCH faster than using only soap and water or a PH balanced lens spray. It is a fact that I have seen with my own eyes.

    It is one thing to clean a lens with isopropyl prior to hard coating, or to wipe a lens down prior to affixing a lens tape for edging, but it is a totally different thing to say clients can just go at it with isopropyl and it will have no effects on coatings.

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    Quote Originally Posted by Mrmessi View Post
    Thank you for all the responses.

    It's a slightly curved frame and she's not doing anything extraordinary with it in terms of cleaning or leaving it exposed in the sun, crazing seems to be in the middle. I have her a easy clean lens, let's see if that fixes the issue.
    Is it a "slightly curved frame" and the lenses are aspheric with a thin center thickness? Jamming very flat lenses into a curved zyl frame will bend them, and over time will craze many of them - especially if the lens was edged with a long A measurement. Best to go spherical or Free form SV here for mounting purposes.

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    Quote Originally Posted by Tallboy View Post
    Craig, using pure undiluted Isopropyl to clean lenses 2 to 3 times a day will wear down coating MUCH faster than using only soap and water or a PH balanced lens spray. It is a fact that I have seen with my own eyes.

    It is one thing to clean a lens with isopropyl prior to hard coating, or to wipe a lens down prior to affixing a lens tape for edging, but it is a totally different thing to say clients can just go at it with isopropyl and it will have no effects on coatings.
    pure IPA should not affect the coating itself, but it will have an effect on the hydrophobic/oleophobic layer

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    Quote Originally Posted by ml43 View Post
    hydrophobic/oleophobic layer
    That seems like an important part of the coating, really.

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    Quote Originally Posted by standarduck View Post
    That seems like an important part of the coating, really.
    But the hydrophobic/oleophbic layer can be reapplied in a minute or so. Yes as good as new.

    The AR part is the most expensive/hardest part to reapply.

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    Quote Originally Posted by ml43 View Post
    But the hydrophobic/oleophbic layer can be reapplied in a minute or so. Yes as good as new.

    The AR part is the most expensive/hardest part to reapply.
    I have so much to learn. Had no idea.

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