Coating Crazed...Why?

**cindiaugustine** · 02-28-2009, 05:23 PM

Didn't have a stellar day at my practicum on Friday. I managed to ruin a lens I was edging by crazing the coating. The lens was an Orma Trio and was probably a bit tight for the plastic frame. In trying to fit the lens in I heated the frame (with the lens in using a hot air frame warmer) and voila, a ruined lens with a crazed coating.

Okay, mistakes happen, all opticians screw up a lens or two, and everyone on my practicum was supportive and took it in good stride. I, on the other hand, am still mad at myself.

So, to get myself over it, I need to figure out exactly what went wrong. Was it the heating alone? Was it lens stress from being pressed into the frame which was too small for it? Was it both? The base curve was off after the incident which suggests that the lens suffered stress. But surely it was stupid of me to heat a coated lens?

I'm nervous now to do even small adjustments to plastic frames with the lens in, and need to solve this in my head.

Are AR coatings really that sensitive to heat? Was it just too much heat? Was it more lens stress + heat, as opposed to heat alone?

I'd like to figure out what happened so I can learn from this and put it behind me. I hate feeling so tentative now about working with frame warmers. :(

Cin

**For-Life** · 02-28-2009, 05:56 PM

Originally Posted by cindiaugustine

Didn't have a stellar day at my practicum on Friday. I managed to ruin a lens I was edging by crazing the coating. The lens was an Orma Trio and was probably a bit tight for the plastic frame. In trying to fit the lens in I heated the frame (with the lens in using a hot air frame warmer) and voila, a ruined lens with a crazed coating.

Okay, mistakes happen, all opticians screw up a lens or two, and everyone on my practicum was supportive and took it in good stride. I, on the other hand, am still mad at myself.

So, to get myself over it, I need to figure out exactly what went wrong. Was it the heating alone? Was it lens stress from being pressed into the frame which was too small for it? Was it both? The base curve was off after the incident which suggests that the lens suffered stress. But surely it was stupid of me to heat a coated lens?

I'm nervous now to do even small adjustments to plastic frames with the lens in, and need to solve this in my head.

Are AR coatings really that sensitive to heat? Was it just too much heat? Was it more lens stress + heat, as opposed to heat alone?

I'd like to figure out what happened so I can learn from this and put it behind me. I hate feeling so tentative now about working with frame warmers. :(

Cin

Probably the heat did add to the problem. Though, I figure that you probably did not have it long enough in there to do it be itself. You probably would do damage to the frame with the heat before the lens. Could be that you were putting too much pressure on the lens too. At the same time, I think there was probably a flaw in the coating on the lens.

Now, with heat, you do have to be very careful. You cannot heat it too long, or the frame will warp, and there could be problems with the lens too.

But the big thing here is you probably did not need the heat to insert the lens. Basically, your lens was edged too large and needed to be cut down. In 99% of plastic jobs, you should be able to cold mount it, but you have to make sure the lens will fit. It is worth it to take an extra little off the lens for a cold mount.

**Happylady** · 02-28-2009, 07:26 PM

I always protect AR lenses from the frame warmer. I either remove them or cover them with my hand or a piece of cardboard. Frame warmers put out a LOT of heat and can craze lenses quite easily.

**cocoisland58** · 02-28-2009, 09:36 PM

Extreme heat will craze even the best of Ar coatings. Remove the lenses before heating the frame (a pain but worth it). I have seen them crazed by dry heat saunas also, twice with the same patient (she had no explanation the first time). I crazed my own by laying my blowdryer too close to them on the bathroom counter. Never did that again.

I always cold mount in a zyl frame much to the chagrin of my boss who likes to cut large and use heat. Mine stay in just as well and the frame likes it better.

**chip anderson** · 02-28-2009, 09:45 PM

Don't think I have ever had an air warmer eat AR but I have had salt pans do this. However after learning AR (pity the AR people don't tell us these things before we have a problem) was heat sensitive, I have always made a point not to allow the lenses to be exposed to heat.
I suspect that's why heat warmers have the little funneling devise (which is missing in some practices) on them, is so that you can direct it away from the lenses and the metal hinges for that matter.

Chip

**billmdee** · 02-28-2009, 10:54 PM

It was probably a combination of both size and heat. Either one could cause crazing, but are usually OK. The flexing of a large lens along with heating causes too much stress on the A/R coating.

I almost always remove any A/R coated lens prior to heating the frame. 1.67 lenses are particularly susceptible to heat induced crazing.

We sometimes have crazing on 1.0 CT finished poly A/R lenses. It seems to be due to chucking pressure and/ or twisting of the lens on the finish blok during edging. We use Slip Stops to help prevent crazing.

Good luck !

**Chris Ryser** · 03-01-2009, 05:57 AM

Originally Posted by cindiaugustine

I'd like to figure out what happened so I can learn from this and put it behind me. I hate feeling so tentative now about working with frame warmers. :(
Cin

The basic layer of an AR coating is SIO2 (silicon dioxide) which is glass and which adheres solidly to the intermediat coating that adheres to the lens surface.

When heated, the plastic lens expand faster than the glass layer with the result that the glass layer start to craze.

People leaving the glasses in the car during summer heat will experience the same thing. Or the person walks from heat into a freezer compartment will also get it.

**THE MEB** · 03-01-2009, 11:42 AM

I might add that I have seen AR craze from being put in an ultrasonic cleaner solution, and turned on, of course, lol

**renee1111** · 03-01-2009, 04:21 PM

Like billmdee said, I always take AR coated lenses out of the frame before adjusting...it is a real pain, but I haven't crazed a lens in years. The other reason I can think of, is when you deblocked the lens, maybe the lens flexed (especially if it was a high minus stock lens with a 1mm CT) If the crazing is mostly central, it's an indication that it happened during deblocking, if not than, it's from the hot air blower. I'm not thinking it's from the lens size, because that would take much longer to craze....weeks even.

I like the subject of the thread, because there's nothing more frustrating than having a patient come back because his coating is genuinely crazed. The first thing they always ask is "why did this happen to my glasses?" These are some of the more obscure reasons I came up with....
-hairspray
- Windex, might be that pt. has actually cleaned glasses with windex or could also be the over spray, when cleaning windows
- Cooks: while reaching into an oven, coatings craze from the extreme heat

**chip anderson** · 03-01-2009, 05:25 PM

Lens alignment plyers can damage coatings.
As to chemicals: Easy off oven cleaner will eat all coatings. If glasses are worn (and something to block the spray from the eye should be because it also eats corneas) and spray gets on them, they're gone.

Chip

**scriptfiller** · 03-01-2009, 06:52 PM

I have a set of trans CR-39 with Avance" I left out in the car and the A/R crazed.

**For-Life** · 03-01-2009, 07:03 PM

Originally Posted by scriptfiller

I have a set of trans CR-39 with Avance" I left out in the car and the A/R crazed.

yep, that is pretty standard. You leave them under the windshield and the coating will craze

**cindiaugustine** · 03-01-2009, 07:06 PM

Thanks everyone, these are all good bits of information. I know we learn more from our mistakes than we do from our successes, but that doesn't make it feel any better at the time. LOL

Cin

**For-Life** · 03-01-2009, 07:17 PM

Originally Posted by cindiaugustine

Thanks everyone, these are all good bits of information. I know we learn more from our mistakes than we do from our successes, but that doesn't make it feel any better at the time. LOL

Cin

I remember that I started at one store. A week into it, a patient came in looking to have his glasses straightened. I put the slightest of pressure on the temple, and it snapped off. Oh, and because we had no area in the back to work, I did this right in front of him.

Now, to me, the frame had to be already damaged, because that much pressure should not have done it, but it made me feel awful nonetheless.

So we have all gone through situations that made us feel bad :)

:cheers:

**cindiaugustine** · 03-01-2009, 08:46 PM

That's what the optometrist I am working with said: "Just wait until you break a frame right in front of a customer...and you will, eventually. These things happen and we recover."

Not looking forward to that but, them's the breaks, as we say. LOL

Originally Posted by For-Life

I remember that I started at one store. A week into it, a patient came in looking to have his glasses straightened. I put the slightest of pressure on the temple, and it snapped off. Oh, and because we had no area in the back to work, I did this right in front of him.

Now, to me, the frame had to be already damaged, because that much pressure should not have done it, but it made me feel awful nonetheless.

So we have all gone through situations that made us feel bad :)

:cheers: