Musings about Glass

[kudapucat]

[glass is] not a supercooled liquid, it's glass. It's a solid. All those stories of glass flowing down over the centuries are bunk.

OK, sorry for the OT, but then why does glass from yesteryear have horizontal flowlines and also is fatter at the bottom always, never the sides or the tops.
If it's a manufacturing issue, why would they all be installed the same way.
Prepared to accept that it's 'bunk' but I need more information or proof.

You're not saying it's a solid suffering from creep are you?

 

[akueck]

It is exactly a manufacturing issue. Glass windows were spun and cut from a disk. One side was thicker (the side toward the center of the disk). Which side would you put down? The thick side, it's most stable that way. So it's also that they were installed the same way, every time. Creep in glass at ambient temperatures is too slow to notice in human timescales. [Creep rates are generally related to homologous temperature, T/Tm where Tm is melting or for glass you'd probably use Tg instead. Tg for window glass is supposedly around 550 C, so T/Tg for a hot day (40 C) is only 0.4 or so. Warm, but not hot enough to cause a lot of creep. Lead for example is about 0.6, so you do see it creep over time, but even then it takes hundreds of years to go far.]

Here's a fun article I found which talks about glass, viscosity, and such. I mostly agree with it.

 

[akueck]

I wonder how the heck they got so dinged up without breaking.

I could explain that too, but I'd need charts and an easel. [bonus movie quote!]

 

[kudapucat]

Seeing a topic he doesn't remember posting, KP came to the slow realisation that he gotmoderated! thanks for the explanation

 

[wildoates]

You engineers are all the same, Aaron.

I only understand a small bit of it, as undergrad and grad were paleontology, not physics or engineering. Too many things to learn, not enough years to learn them all!

 

[Golddiggie]

I was always told that old glass, before modern processes were in place, were more 'fluid' than what's currently produced. Fluid in the aspect that it could 'settle' a little over centuries (if it survived)... The chances of you seeing it do so in a normal lifespan is virtually nil. Modern processes are producing more stable glass, especially tempered glass, than before.

Although the 'spun' comments also makes sense, so that could be what was really going on and the people looking at the glass (supposed 'experts') simply had it wrong. IF glass actually does settle over time, I think you would need a very accurate micrometer in order to measure any thickness difference over a normal life span... It would be interesting if someone could take a sheet of glass (not tempered, or at least include non-tempered glass in this), suspend it in a controlled environment (replicate the thermal variances we see in the US) and see what happens to it over time. It could be that even with ultra-precise tools, we won't see any change in thickness (from top to bottom) after getting accurate, initial, measurements... It would put the matter to bed for good though...

This could be simply a matter of different manufacturing techniques making for differences... Such as old school forging (like from 300+ years ago) compared with today's forging, or casting of steel products. Back when it was 100% human powered forging, you wouldn't expect to have the exact same thickness (down to 1/1000th of an inch) across an item (unless it was short)... With how forging is done today, you actually can achieve that level of precision (if not higher)...

For something where you want to ensure that solvents won't impact, go glass... Otherwise, pick your pleasure...

 

[akueck]

Creep in glass would take many tens of thousands of years to measure at ambient temperature. I sincerely doubt anyone would care so much to look into it on that time scale. When T/Tg is less than 0.5, you can pretty much forget about creep for as long as your civilization is around.

The whole "glass is a liquid!" thing is one of those half-truths that gets spread around to make people sound smart. It's one of the cases where someone with a little knowledge is actually dumber than one with no knowledge at all. Unfortunately it's such a cool story that it will be very hard to root out of popular science. Same goes for mead, honey, and honeymoon. The relationship between mead/honey and honeymoon is tenuous at best, but it gets repeated over and over again and now it's true. Only it's not true. Ugh.

For what it's worth, here is a nice definition of "solid" and "liquid" that you can use to show your friends that glass in indeed a solid: A solid can resist a shear force (of a reasonable magnitude of course). A liquid can not resist a shear force, but will flow (with some measurable viscosity). Go ahead and apply a shear force to your window; does it move? Nope! It's a solid. It has a shear modulus and everything.

Extra trivia: you can make metallic glass (for your golf clubs!). No one has ever said that metallic glass is a supercooled liquid that is slowly flowing, everyone knows it is a solid. An ultra-low damping solid, good for bouncing ball-bearings (but alas, not so great for golf clubs). Hopefully no one gets confused by the word "glass" and starts talking about liquid metal that isn't liquid, but I figure it's only a matter of time.

 

[Golddiggie]

Hopefully no one gets confused by the word "glass" and starts talking about liquid metal that isn't liquid, but I figure it's only a matter of time.

Isn't that what mercury, technically, is? Not that I would want it anywhere near my foods, or me, unless properly contained at least (not even then near my foods or brewing equipment)...

Learn something new at least every few days it seems, on these boards...

 

[akueck]

Mercury is liquid at room temperatures, sure. But it's not a glass by any stretch, it is really a liquid. Gallium is a liquid right above room temp, but again it's a straight up solid otherwise. Metallic glass is like silica glass in that it is a disordered solid. And it gets there by frustrating the crystallization process. They are both glasses in the same sense. And both definitely solid, metallic glass is big in the fracture research area now (after some guys published data overestimating it's toughness by a factor of 3 or so).

 

[Golddiggie]

I was referring to mercury as a liquid metal, not glass...

 

[AToE]

For what it's worth, here is a nice definition of "solid" and "liquid" that you can use to show your friends that glass in indeed a solid: A solid can resist a shear force (of a reasonable magnitude of course). A liquid can not resist a shear force, but will flow (with some measurable viscosity). Go ahead and apply a shear force to your window; does it move? Nope! It's a solid. It has a shear modulus and everything.

Then there's non-Newtonian fluids which have a little fun with what liquids are supposed to do when hit with some shear force.

Those are fun, I can see them being usefull in body armour one day (totally fluid and flexible until something hits it hard, it'd be perfect if you could create one with just the reactions you wanted).

 

[YogiBearMead726]

Then there's non-Newtonian fluids which have a little fun with what liquids are supposed to do when hit with some shear force.

Those are fun, I can see them being usefull in body armour one day (totally fluid and flexible until something hits it hard, it'd be perfect if you could create one with just the reactions you wanted).

Those are awesome!! I've still tried to keep up on science developments after stopping science classes (if I wasn't addicted to making music, I probably would've majored in bio-chem/botany. I guess even enology since I went to Davis for awhile...), and this is one of the coolest things I've seen! This, and dragonskin armor made from ceramic discs overlapping. Though the non-Newtonian fluids seem a bit more practical. But, then again, I am just a lowly musician, not an engineer...

 

[kudapucat]

Then there's non-Newtonian fluids which have a little fun with what liquids are supposed to do when hit with some shear force.

Those are fun, I can see them being usefull in body armour one day (totally fluid and flexible until something hits it hard, it'd be perfect if you could create one with just the reactions you wanted).

You mean like a solution of cornflour or arrowroot and water? That stuff's FUN.

 

[AToE]

You mean like a solution of cornflour or arrowroot and water? That stuff's FUN.

Yup, very fun.

 

[Golddiggie]

You mean like a solution of cornflour or arrowroot and water? That stuff's FUN.

That's the first time I've ever heard of a simple thickening solution being called "fun"... Then again, I think it's more 'fun' to make a good rue... Also much more useful... I've been using rue as a thickener over anything else these days... Thickens things easily, is easy to make, AND adds flavor (fat IS flavor after all)... ;D

 

[AToE]

That's the first time I've ever heard of a simple thickening solution being called "fun"... Then again, I think it's more 'fun' to make a good rue... Also much more useful... I've been using rue as a thickener over anything else these days... Thickens things easily, is easy to make, AND adds flavor (fat IS flavor after all)... ;D

Have you ever played with a cornstarch and water goop though? It's a non-newtonian fluid, when hit with sudden force it behaves more like a solid, but then quickly reverts back to behaving like a liquid. You can pick up a blob of it, then rip it, and it actually sheers, and you can handle it like a dough if you keep it moving and reacting to forces, but as soon as you try to just hold a ball of it still in your hand it'll go back to being a fairly thin fluid and run right through your fingers.

It's seriously pretty fun, I remember it being a huge hit when I was a little kid in school!

 

[kudapucat]

It is fun, I still play with it these days on occasion especially if some1 says they've never seen it before.
I enjoy making custard from powder for the same reason.

If you make a batch of cornflour, arrowroot, custard powder etc, with as little water as possible, you'll see what we mean.
Seriously, get some out of the cupbpoard and have a play. You can scoop off a big chunk with a spoon, only when you take the time to look at it, it turns ot warer and runs away.
you can put something heavy, or your finger ont he surface, and it will sink, but you can punch this as hard as you can, and barely make a dint.
Hours of non-newtonian fun!

 

[AToE]

The punching thing is the most fun, and what makes me think a more advanced version would be perfect for armour. I love how you hand can go in as easily as into soup if you're gentle, but you could probably hurt yourself punching a big bucket of it.

 

[kudapucat]

I've always been too frugal to make a big bucket of it, but now you have me thinking. How about a swimming pool full?
It could be a gameshow thing where you've got to do something difficult and timeconsuming above a pool of non-newtonian fluid....
the difficulty comes in if you slow down, you'll sink, and then have to try to 'gently' swim out! it'd be hillarious!

Let's pitch it to the "Wipeout" producers. If you don't get your timing right and you pause then you get stuck in shin deep gunk!

 

[AToE]

I've always been too frugal to make a big bucket of it, but now you have me thinking. How about a swimming pool full?
It could be a gameshow thing where you've got to do something difficult and timeconsuming above a pool of non-newtonian fluid....
the difficulty comes in if you slow down, you'll sink, and then have to try to 'gently' swim out! it'd be hillarious!

Let's pitch it to the "Wipeout" producers. If you don't get your timing right and you pause then you get stuck in shin deep gunk!

I think I've actually seen footage of someone running around on top of a pool of the stuff, and then stopping for a brief moment and almost instantly sinking (wasn't deep).