Or just casting the blanks with a hole already in them? I assume those blanks are molded from liquid glass. Put a pin in the mold.
(This assumes that the holes are a standard location and size, which I suspect may not be the case.)
I was an optician for 15 years. It’s not impossible to drill holes in glass lenses, it’s just impossible drill holes in them and have them meet impact resistance standards. Unless things have changed in the last 10 years or so, glass lenses have to pass a drop ball test before they can be used in prescription eyewear. That means they have to withstand a 5/8 inch steel ball being dropped from a height of 50 inches. And the test has to be done after the lens is completely finished.
Beyond that, rimless frames are somewhat fragile to begin with, and glass lenses, being heavier and more rigid, put a lot more stress on the frames. In my 15 years of working with them, I came to hate glass lenses with the fire of a thousand suns.
Also, anything that can scratch plastic lenses (Lenses don’t scratch themselves. Something has to happen to them.) can scratch glass as well, it just takes longer. And with glass lenses any damage compromises the integrity of the glass, making them more likely to break the next time something happens to them.
Making optical glass requires that the glass is cooled over a critical point - the fictive or glass transition temperature - very slowly in a process called annealing. Not doing so will mean that the glass body will not have a uniform refractive index as stresses will get ‘frozen’ in to the glass as stressed glass has a different RI than unstressed*. This extra care is part of the reason why optical grade glass is more expensive than regular glass. Melting holes will necessitate transitioning part of the lens through this temperature and ruin the optical uniformity of the lens.
*Annealing is also required for normal glass, otherwise the stresses can make the glass prone to shattering suddenly. For normal glassware however, the process is less critical and can be done faster and cheaper.
What if you melt the holes instead?
Really? I’ve had a particular problem with mugs - china - scratching my plastic-with-coating spectacles which I didn’t have with glass spectacles.
Does that still apply if the hole is melted? After all, bottles have a huge hole in them.
It doesn’t matter. The hole is a problem regardless of how it got there.
You’d be amazed at how many glass lenses I’ve seen with scratches on the back side that came from fingernails. Took a few months of frequently rubbing their eyes without removing the specs. Usually farm or other outdoor workers. Second most common cause of scratches, after improper cleaning. Easy to tell which, because cleaning scratches tend to be on both sides and circular, while fingernail scratches tend to be diagonal toward the upper center corner of the lens and just on the inside.
And glass lenses aren’t warranted against scratching. Plastic and polycarbonate lenses usually are. The last couple of years I was in the business the cost difference between lenses with scratch resistant coating and without was so small that we didn’t even sell uncoated lenses anymore.
Not sure how a ceramic mug could be scratching lenses. It shouldn’t even be coming into contact with them.
Not the ones I’ve been wearing. And I had them put on their toughest anti-scratch coating.
I forget the cost but it wasn’t trivial.
It’s very easy: just raise the mug so it contacts the glasses. Like when you’re draining a mug.
Then you got ripped off. All polycarbonate lenses have a one year factory warranty against scratching, as do all coated plastic lenses. Unfortunately there’s no requirement that the shop honor that. I remember there was at least one dishonest shop in the area that charged for replacements but still send the scratched ones back for credit.
When I first started in the 90s a scratch resistant coating increased the wholesale by about $10, which translated to about $20 retail. At the time I left selling uncoated lenses would have only lowered the retail price by less than 10 bucks on single vision and lined bifocals. Progressives were all coated for as long as I was in the business. We couldn’t get them uncoated even if people asked for them, and if anyone charged extra for that it would have been borderline fraud.
But then we were aware of places that would charge extra for a “breakage warranty” on the frames, even though most of the frame manufacturers gave a 2 year no questions asked warranty.
I don;t think it would be a problem to drill a hole near the middle of a glass lens, but that would be a pretty lousy mounting point for the arm or bridge of a pair of glasses - putting the hole near the edge of the lens just expects a lot of performance from a relatively small section of glass. Glass is typically both less flexible than, and of lower tensile strength than optical plastics - so less forgiving of abuse or even normal kinds of forces in this context
Like many substances, glass expands when hot, and contracts when cold. In the case of glass, this can be fairly significant.
If the outer layers of the glass cool rapidly, they contract and fix into place around the hot, expanded interior glass. As the interior subsequently cools, it also tries to contract, but is fixed in place by the cooled exterior. This process creates internal tension throughout the glass material. Very often, glass objects created like this can spontaneously shatter due to this internal tension.
The classic example of this internal tension is the Prince Ruperts drop - a bead of molten glass dropped into a bucket of water that forms a teardrop with a long glass tail. The head of the drop is under extreme internal tension - it can withstand a hammer strike. If the thin tail is clipped or broken, the surface tension starts releasing and the entire drop explodes into shards of glass.
Annealing is the process of lowering the glass temperature slowly, so that the outside of the glass cools down at the same rate as the interior, preventing the internal tensions of glass that has not been annealed.
Bottles are moulded in that shape, and yes - glass bottles need to be annealed to prevent them from shattering.
If you drill holes in glass, you have to keep the glass and bit cool enough to prevent melting. If you melt a hole, you then have to anneal the glass.
Fascinating.
A couple of things from the OP just occurred to me:
First of all, if the person the OP talked to was really a qualified optician he/she should have known why you can’t put glass lenses in a drilled rimless frame. Unfortunately in most states there’s no rules or laws preventing anyone from claiming to be an optician without having some kind of evidence that they know what they’re doing.
Also, being impossible to get them doesn’t mean it’s physically impossible, just that it’s not legal. I started as an optician in 1991, and it hadn’t been horribly long since it was legal to sell untempered glass lenses, or put them in drilled rimless frames.I saw a fair number of antique specs that had glass lenses in drilled rimless frames, some of them still being worn (by people who got mad when we told them we couldn’t put glass lenses in them anymore.)
He’s most certainly a qualified and certified optician. And I asked him about a melted hole, not a drilled hole. I just expect that it’s been a very long time since someone asked him such a question.
But again, it’s the hole that’s the problem, regardless of how it got there. And he should know that.
Until relatively recently, some sunglass manufacturers offered rimless frames with glass prescription lenses. For example, Maui Jim had a line of rimless beta-titanium frames with glass sun lenses that could be ordered in prescription form. The catch was that the Rx lenses came from the factory. I assume this took care of the drilling issue because the lenses were cast with the holes already in them.
I owned several pairs, and I can tell you that the real problem with rimless glass lenses is that they’ll shatter the second you drop them because there’s no frame to protect them. I never had a pair last long enough for the lens mounting hole to weaken; if anything, that was more of a problem with rimless polycarbonate/CR-39 lenses.