Can you tell me how any other mineral than crown glass is hardened? From my understanding heat or chemical hardening are done only on crown glass. Are higher index lenses (1.6-1.9) not crown glass but flint or barium? Thank you for answering.
Can you tell me how any other mineral than crown glass is hardened? From my understanding heat or chemical hardening are done only on crown glass. Are higher index lenses (1.6-1.9) not crown glass but flint or barium? Thank you for answering.
All glass can be be chemically hardened. Labs use an ion exchange process which can be altered depending upon the material. Untreated glass is dangerous and should not be put in front of your eyes. At least this was the case up to a few years ago. We stopped processing glass due to general lack of interest :0)
shutterbug
I'm not sure that all glass lenses are required to be hardened...Laminated lenses (polarized) being chief among them. Heat treating a polarized glass would be a mess. Fun to try though I bet. I wonder, can you chem temper a laminated glass lens?
AA
NO!!!! Do not harden a polariod by any method.
No laminated lens is to ever be hardened.
All non photochromic lanses are chem tempered in KNO3....Potasium Nitrate
Photochromic lenses go in NaNO3...Sodium Nitrate
Air hardening is only recomended for lower power lenses different hardening systems go by average thickness or by weight of the lens as well as the material and color it depends on the hardener being used.
I once had the misfortune of heat treating a laminated lens....it flamed up in the air hardening unit. Chem hardening it would have caused a real problem because the chem bath is a strong oxidiser
Ed
CoWorkers accidentally Heat treating CR39 Lenses is also an entertaining event.
AA
I had a tech air harden CR-39 by mistake too. The stink of burning plastic permeated the lab. I was at the other end of the lab walked to the hardener picked up a pyrex dish of water and a pair of lens calipers with metal tips turned the timer to the start of the cooling cycle removed the flaming lenses with the calipers and dropped them into the water.
By the way this happened in a Lenscrafters in front of customers looking into the fishbowl lab and my boss was looking at what was happening. He was most impressed by my cool handling of a very hot situation
Ed
I always wondered when I worked for LC what the customers thought when things like that happened. I wanted to see if Alcohol would ignite if sprayed into the heat treater at 1200 F, or if it would evaporate before it had a chance... sort of like a chemistry/physics experiment...It didn't evaporate. Forgot the patients were watching...
THe alcohol mist may vaporize but the vapor is still flamable. At 1200-1225 F that is probably quite a sight
Ed
Please note: It is the vapor+oxygen or air that burns with most liquids. Few if any will burn before vaporizing. Don't assume vapors will not burn. Been on fire before and it wasn't nice.
Chip
Ahhhh...The good old days, I heat treated a laminated lens many years ago. It was quite a site. I also enjoyed soaking poly lenses in acetone. Those were the good ol days. :D
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