Re: glass

[Jim K..]

Seen it in concrete blocks.

[Broadback]

i understood that glass is effectively a liquid, therefor over time it flows to the bottom making it thicker.

[The Natural Philosopher]

IIRC this was was shown to be a myth, but I cant recall te references

[Pancho]

[AJH]

When glass was spun rather than floated and then cut into panes the part from nearer the periphery was thinner, so it was laid upwards.

Glass is not a supercooled liquid, pitch is.

AJH

[Broadback]

Thanks I stand corrected.

[John Rumm]

Yup

That's a myth. What you see is just an artefact of the way flat glass was made at the time - by glass blowers expanding, then flattening and spinning a disc of material. Once a rectangular section was cut from the disc, the bit from nearer the edge of the disc was usually a bit thicker, and glaziers would install the thicker section to the bottom.

Glass is only a super cooled liquid briefly in its manufacturing process

- and the temperature falls below the transition temp. It becomes an amorphous solid - which is a state that is neither fully solid or liquid. The atoms do have more mobility that in a solid, but not enough to see any visible changes with the human eye over time.

[Only ever had ONE class A Callsign ...]

yes I love old glass so lumpy !

[Only ever had ONE class A Callsign ...]

interesting ...thanks...so the glasgow collage of building was wrong in

1971....tee hee

[Martin Brown]

Nobody has. You would have to wait geological timescales to see it happen even slightly. Back in the days before float glass they would always install it with the heavy thick side down since it is more stable and lets in very slightly more light with the prism facing skywards.

The only possible exception is sugar glass used in stunts. That might flow on a similar timescale to pitch in a warm dry environment.

Pitch on the other hand will move on decadal timescales.

[Brian Gaff]

Are there some types of glass we cannot put in the recycling? It seems there is but nobody can tell me why or which it is! Brian

[Martin Brown]

They are both supercooled liquids but the viscosity of conventional glass is so very high that it is effectively dimensionally stable. You can make diffraction limited optics out of it and they stay in shape.

However, some formulations of clear flint glass used in early telescope lenses were metastable wrt surface crystallisation. The original 12" Cauchoix doublet lens on the Northumberand telescope in Cambridge suffered this problem with the surfaces of one component of the doublet misting up with the formation of microcrystals. They refigured it a couple of times but in the end it was simpler and better to manufacture a new modern design doublet lens and put the original into store.

[Max Demian]

Only glass bottles or jars are wanted.

[Martin Brown]

They don't like you putting window glass in with clear flint glass bottles. The formulation is slightly different to bottle glass.

Window glass is typically disposed of as "hard core".

Container glass is optimised to resist water marking.

Adding broken window glass to it degrades the quality.

Long buried glass eventually develops wonderful iridescence.

[Nick Odell]

Here. Try this:

Nick

[NY]

Interesting that several of us have seen references in physics books etc to glass flowing over measurable time (eg over a century or so), leading to window panes being thicker at the bottom. I agree that a better explanation is the spun-glass method of making old glass causing glass to be thicker at one edge, and this was conventionally put at the bottom of a pane.

I didn't know about not being supposed to put window glass into bottle bank recycling. I didn't even know that it was a different composition.

I tend to wrap broken glass (eg from a window pane) in newspaper, snap it into manageable pieces and put it (wrapped and sealed with sellotape) into the normal landfill, non-recyclable dustbin. Interestingly, the last time I had some broken window glass and I took it to the tip along with a lot of other rubbish, the guy said to put it in the bottle bank rather than landfill or hard core. Seems that he was wrong!

[The Natural Philosopher]

I am oputting my broken window glass in my own landfill. It's graat to have a dry ditch in need of filling with assorted hardcore and exhausted weed filled gravel

[Andrew]

when I replaced a couple of 1976 single glazed boulton and paul windows a couple of years ago, I carefully knocked the old frames apart into timber and broken glass, but the local recycling place told me to chuck the glass in the general waste skip.

[Chris Hogg]

They don't like 'pyrex' type glass in there, either. Also a different composition, borosilicate glass, whereas window and container glasses are soda-lime-silica glasses of different compositions, due to the different requirements both in manufacture and in use.

[Marland]

Did you originally dig it for the ex wife ?

GH