Glass a Liquid?

We are confused...what about glass blowers who melt chunks of glass in the kiln to reform into whatever glass product they are creating. Not to mention glass recycling. Where do they come up with glass not having a melting point?

Lori
 
Glass is classified, or glassified if you prefer, as a liquid. If you've ever seen windows in an old house, where the glass appears thicker at the bottom, it's because the molecules have "dripped" like pancake syrup down the side of the bottle. But much slower of course.

Because of these moving molecules, you must break glass very soon after scoring it or the score line will heal enough to prevent a clean break.

Paul Cascio
www.pictureframingschool.com
 
I know that we have been through this one before. And before, and before that too!

But I just learned something new (to me at least)about the whole 'glass is liquid' thing that seemed to make sense.

One of the qualities of a material in its liquid state is that you can change the shape by breaking the surface tension. Ever touch a droplet of water on the hood of your car? Break the suface and it can be moved. Break the surface tension of a pane of glass and it can be moved.

This is why glass breaks the way it does. But then I asked this guy (a materials engineer)what about ceramic? It cracks just like glass. His reply was that you apply heat to a raw ceramic material to convert it into the rigid form. That change is final, you can never be return the rigid ceramic back to the raw state. However, with glass, heat makes it more of a liquid, not a conversion to rigid form. You 'cook' ceramic, but you melt glass.

help.gif


The final point he started to make is that there is no other material that cuts, by hand or machine in exactly the same way as glass. And then we were interrupted.
 
glass is a liquid = true
I've seen thinner glass at top in frames, glass paintings, and old windows. The older the thinner. The thinnest was 250 years old and about 1/4 inch on bottom and almost unmeasureable on top it was so thin. What messes up the equation is special glass like tempered or special properties glass that might not show the same flow as regular glass used in windows.


glass healing = false
I once scored 12 pieces of glass and let them sit.
after one day 1st piece broke fine.

waited a month same result
next month ditto
...
for a year and every light broke clean.

If it is not healing in a year I believe I proved my point.

The above is true and I believe in my statement.

framer
sleep.gif
 
The glass being a liquid is a MYTH.
Old glass is often called 'spun' glass.
HERE and HERE are article's that explain it better than I can.
 
Take a cold ceramic mug. Tap with spoon. Get the tone and remember it. Now fill same mug with hot liquid. Tap again. Different sound. Usually more dull and a totally different tonal pitch.

Basic organic chemistry and molecular motion theory. Unfortunately, I slept thru organic and inorganic
 
Cold glass flowing is bunk! The strongest argument against it is tempered glass. Tempered glass is made heating it to the softening point and cooling the surface with air jets. This makes the surface cool and and immobile. The middle region is not quite solid as it has not cooled yet. As the glass in the center cools and shrinks slightly, it pulls the cold surface into intense compression. 1000s of pounds of per square inch, in fact. If the surface of the glass is breached in some way, such as a deep enough scratch, the inner material that is in tension, as it is tries to compress the outer surfaces, rips itself apart violently and sheet of glass “pops” into a bunch of small cubes as the potential energy is released all over the sheet.

Now, if glass flowed at room temperatures, this intense tensile and compressive forces would simply vanish as the glass flowed from the forces seconds after it was made. However, old tempered windows will still break into cubes showing the tempering is still in effect. If you took a tempered sheet of glass and heated it evenly to the softening point, and let it slowly cool (so no new stresses form), it would become non tempered and would shatter like regular glass.

Lori, The key term is melting *point* . Many amorphous solids get softer as as they are heated. There is no specific temperature at which the material suddenly turns liquid as with ice to water.

John
 
HOGWASH! Get back to work an quit wasting time.

John
 
Originally posted by pcascio:
If you've ever seen windows in an old house, where the glass appears thicker at the bottom, it's because the molecules have "dripped" like pancake syrup down the side of the bottle. But much slower of course.
Paul Cascio
Does this mean that if you flip the windows vertically (the bottom becomes the top), the glass will "drip" from top to bottom, and at some point over the next bizzillion years will flow back down?????
party.gif
party.gif
party.gif
party.gif
party.gif
 
Many lites of old glass may have been made using
the cylinder process and that may account for their irregular thickness:
Cylinder glass
A technique for producing sheet glass dating from the 11th century. By blowing a hollow glass sphere and swinging it vertically, gravity pulls the glass into a cylindrical "pod" measuring up to 3 metres long, with a width of up to 45 cm. While still hot, the ends of the pod are cut off and the resulting cylinder cut lengthways and laid flat.
Acting as a super-cooled liquid, the movement in
glass is far to slow for it to run in an architectual setting.


Hugh
 
Back
Top