# Optical Forums > General Optics and Eyecare Discussion Forum >  Why do lenses craze?

## Mrmessi

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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## becc971

whats she cleaning them with?  i had a guy who cleaned his with alcohol every day and that happened.

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## Slim

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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## becc971

> 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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## Wes

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?

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## standarduck

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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## mervinek

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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## nicksims

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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## Dave E

denture cleaner on them that a new one

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## other_bill_fea

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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## MBD

+1!

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## Chris Ryser

> *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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## abberated

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

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## sharpstick777

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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## 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.

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## globaljp

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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## Craig

> 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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## Craig

> 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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## Mrmessi

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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## Tallboy

> 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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## Tallboy

> 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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## ml43

> 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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## standarduck

> hydrophobic/oleophobic layer


That seems like an important part of the coating, really.

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## ml43

> 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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## standarduck

> 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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## Tallboy

> 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.


While this may be true to a point, this is faulty logic for two reasons.  1) Once those layers are gone/damaged the AR stack itself is vulnerable to a myriad of real life chemical contaminants and abrasive gritty substances that will permanently damage it - in the non sterile AR lab environment that my face cheese faithful meander in daily.

2) The AR may be the most expensive part of the process, but I can get a cheap AR stack applied to a lens for 20 something dollars.  The best of the best ARs (which I deal in almost exclusively) are pushing 3 to 4 times that amount.  If the extra coating processes these were put through equated to a simple siloxane dip coating a la Chris Ryser they would not cost so much, nor would there be such a difference in scratch/chemical resistance among them all.

Again, advise your clients in your way, I will tell them to use soap and water, or my lens cleaner.  If that doesn't work I ask them to bring the lenses to me for the use of harsher chemical agents.

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## ml43

> While this may be true to a point, this is faulty logic for two reasons.  1) Once those layers are gone/damaged the AR stack itself is vulnerable to a myriad of real life chemical contaminants and abrasive gritty substances that will permanently damage it - in the non sterile AR lab environment that my face cheese faithful meander in daily.
> 
> 2) The AR may be the most expensive part of the process, but I can get a cheap AR stack applied to a lens for 20 something dollars.  The best of the best ARs (which I deal in almost exclusively) are pushing 3 to 4 times that amount.  If the extra coating processes these were put through equated to a simple siloxane dip coating a la Chris Ryser they would not cost so much, nor would there be such a difference in scratch/chemical resistance among them all.
> 
> Again, advise your clients in your way, I will tell them to use soap and water, or my lens cleaner.  If that doesn't work I ask them to bring the lenses to me for the use of harsher chemical agents.



you do realize that the difference between a house AR and "crizal" and the like is mostly just a name and marketing.

most labs only have one AR machine.

house AR and crizal is done by the same machine.  the only real difference is the crizal coatings line essilors pockets.

like wise with the hydrophobic/oleophobic coatings.

yes ones that are done in chamber do last a bit longer and have slightly better QC.  but I bet if I didn't tell you the difference, you wouldn't be able to tell the difference between a crizal AR and a brand A AR.

Chris isn't the only on that sells and uses wipe on hydrophobic/oleophobic coatings. 

almost all jobs that come from eyemed use wipe on  hydrophobic layers.

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## Outkast

Originally Posted by *Craig*                  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. 


Check out my thread on this subject, Alcohol is getting ruled out I think do to the punishment I am putting these coatings through, but opinions still seem to very. /shrug just sayin :Wink: 

My mom roasted a set pulling a pizza out of the oven though, I think heat as most said and lens flex are the main culprits.

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## cowboytelemark

I found this older thread while researching different lens cleaners.  In my experience, most of the time crazing on a new pair of glasses is due to the combination of heat and stress during frame adjustment, especially with a dramatic zyl adjustment.  Try popping your lenses out, adjust frame with demo lenses in, then re-insert the Rx.

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## Uncle Fester

> but I bet if I didn't tell you the difference, you wouldn't be able to tell the difference between a crizal AR and a brand A AR.


Dot the lens with a Sharpie and it will bead on the better (Avance) coatings. Never found that true on cheaper ones. Now if we're talking about Crizal Zeiss SET etc. I don't see a big difference either.

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## Uilleann

There is much silliness in this thread!  Wish we still had the popcorn imoticon.  :)

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## Gizzo

> 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.  
> ...



+1

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## smitan

Hi All,
         Want to know what causes the Crazing of the hih index lenses specially 1.67? What manufactuing defect in AR can cause the problem? Is it dependent on the layer thickness of the entir stack or single layers like  SIO2 ,Zro2 or is it the parameters of etching like anode current,anode voltage,neutralizing current etc?

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## lensmanmd

> Hi All,
>          Want to know what causes the Crazing of the hih index lenses specially 1.67? What manufactuing defect in AR can cause the problem? Is it dependent on the layer thickness of the entir stack or single layers like  SIO2 ,Zro2 or is it the parameters of etching like anode current,anode voltage,neutralizing current etc?


167 is prone to expansion/contraction, so heat is the primary cause of crazing.  Secondary cause is block mismatch @ bench, causing internal crazing at the edger.

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## smitan

> 167 is prone to expansion/contraction, so heat is the primary cause of crazing.  Secondary cause is block mismatch @ bench, causing internal crazing at the edger.


Can you please suggest how to proceed with it as our customers complain about crazing in 1.6 index and 1.67 as well.Can we adjust something in the AR stack ?

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## lensmanmd

I need to ask.  Is the crazing occurring in coater?   Plus or minus?
I would suspect not, as it would be noticeable at AR inspection, or at first inspection.    More likely a bench issue, esp., since you mention 1.6, which is more stable.  
Then this.  If it is a bench/edging issue, it should be caught @ final.  
This leads me to believe that it is happening at dispensing, when the optician is fitting the frame.

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## Uncle Fester

If this is a Thai sun then this might be the problem. 

My understanding is at about 130 degrees Fahrenheit  (54.4 C) crazing can occur.

I've had someone who left them in a roof auto compartment for glasses in very hot weather produce crazing.

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## smitan

> I need to ask.  Is the crazing occurring in coater?   Plus or minus?
> I would suspect not, as it would be noticeable at AR inspection, or at first inspection.    More likely a bench issue, esp., since you mention 1.6, which is more stable.  
> Then this.  If it is a bench/edging issue, it should be caught @ final.  
> This leads me to believe that it is happening at dispensing, when the optician is fitting the frame.


Thankyou for replying. No this is not occuring at the coater. The complains are coming from the customer after 1 monh of use...

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## Jim Schafer

once upon a time The Vision Council AR Committee created a poster of most common AR failures, six to eight captioned photos. It was very helpful to trouble shoot. I recall every member of VC and OLA received hard copies and it was also downloadable. Supposedly, anything on the internet cannot be lost :). 

best regards and stay healthy!

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