GLASS prescription lenses

[Gale Hawkins]

Most offices today just do not have equipment to work with glass but it can be farmed out to the big labs.

 

[the old grind]

Anyone who's done much welding will know that spatter sticks to glass & bounces off plastic. Technically, it must have to do with the specific heat of either material. Apparently, glass (sometimes with metallic ingredients in its recipe) will absorb heat in nano-seconds. This micro-preheating allows spatter to fuse to a glass lens, not so with plastic's lower density, lower specific heat, and polymer make-up. Been there both ways, many times.

My moderately stiff prescription of 55+ years (5-6 diopters) had long meant glass glasses sliding down my nose. Polycarbonate among the plastics, is barely thicker than glass of similar refractive properties, and is all I've ordered since it became available. I ask for 'scratch coat' and keep hearing that "it's included", ... as a charge is added to my co-pay.

One thing I'll never have again on poly-carb lenses is 'anti-glare' coating, which peels loose in mere weeks. :thumbdown: (It's easily spotted by a greenish tint to on-lens reflections.)

btw: Beware of brake fluid among all other 'everyday' shop chemicals when wearing plastic lenses. It will spiderweb poly-carbs on contact, just like it'll ruin gauge lenses if spilled when topping up the brake reservoir on your bike's handlebars. (You can't wipe it off fast enough.) I must have had a smidge on my hand when reaching to adjust while doing a brake job recently. My brother spotted cracked edges on this pair before I ever noticed. Doesn't take much to do the damage. I caught drips working under cars on the assembly line years ago, and lenses would go south during that shift. :2cents:

 

[3930dave]

Brake fluid is nasty stuff.... An optometrist I asked about occasional gas and diesel splashes said plastic was OK, but I didn't think about brake fluid at the time. Yes, never having owned plastic lenses I was wondering about chemical deterioration. Granted, most flashlights use pretty cheap plastic for lenses, but many tend to be affected after being in use around a garage for a while.

I also recall liquid Muskol (the old high DEET stuff anyway) doing a real number on the plastic shield on a camping lantern.

Thanks to this thread I now have a few recommended web sources to try for a glass solution. :thumbsup:

Rgds, D.

 

[dusty3030]

I really preferred glass for years. Plastic scratched like all get out in a short period of time; however, the last few years have been better. All boiled down to cleaning.
ALWAYS have a clean made for plastic lenses micro fiber cleaning cloth and a little spray bottle of cleaning solution for plastic lenses with you. The cloths come in little plastic sleeves to keep them clean and are washable.
I keep one in each vehicle, big bottle and cloth in my desk at work, big bottle and cloth at home.
Learn to wash away the grit, use a light touch with a cloth, and watch how you store them. I used to rub hard on glass lenses with a cotton t shirt. When I would clean plastic lenses the same I didn't realize I was rubbing the hard coating off of them each time. Took no time to ruin them.
Using the right stuff and never ever using a paper towel or anything that would scratch them they last as long as glass and are much much lighter.

 

[3930dave]

Thanks for sharing your hard earned experience Dusty - those comments may well save somebody's plastic lenses.

Personally (everybody differs on this, as this thread has readily shown), I break the comparison down this way in terms of drawbacks:

Glass:
Higher weight - a Don't Care in my case.
Higher cost - haven't won a major lottery, but feel that the cost adder for glass is not objectionable
Impact resistance - safety glass is adequate for my needs

Plastic:
Optics - need best quality plastic/coatings/cutting algorithms to approach glass optics
Abrasion - needs more care and special cleaning
Chemical exposure - sensitive to some typical automotive chemicals, likely some household ones too

In my case, the relative (to the utility I get from my glasses) cost savings realized from going to plastic does not justify the drawbacks. Real, or perceived .

This has been an interesting discussion. Informative, esp. re. plastics performance in metal working applications.

Rgds, D.