Your statement assumes a fact not in evidence. The point is the glass worker couldn't see the difference by eye on each pane and they couldn't achieve the consistency of thicker at the bottom by chance. It depends on what era of glass making you are referring to. Some of the glass would require very good measurement to tell the difference in thickness, or are you saying that you can just look at a pane of glass and tell that one end is 0.001 inch thicker than the other? And some rolled glass has so many waves and bubbles, one couldn't decide which end was thicker.
The rule of thumb for mirrors in telescopes is to make them only six times wider than they are thick to prevent them from sagging under their own weight.
For scary sharpening or waterstone flatening I use a ground and polished concrete fake granite plate of the kind used in garden paths, I cannot detect any deviation from flat with a straightedge and it was cheap, about 3EUR for a 40cm times 40cm size.
because your science teachers told you it does, doesn't mean they were right. The folks at alt.folklore.urban are damn good about breaking things down, and if you have something that isn't covered in their FAQs and is truly new information, they'd love to know about it.
well, actually, yes. it also doesn't having anything to do with the making of the glass, since they are still making glass the same way as 5000 years ago. shovel the raw materials into an oven. heat. pour out.
haha. please provide some cites as to what you are talking about glass flowing. as has been pointed out by others, that's been debunked quite a while ago.
i'd probably, without looking at it whilst it was scratched, have to say it wasn't really a scratch but some other mark on it. i've got glass that i've scratched or scored over 20 years old. i hae some other glass that i took out of an antique window that must have been 75 years old. they haven't healed yet and i'm not holding my breath.
If you're talking about the oldest examples of glass then you most certainly can see the difference in thickness by eye. These are also the examples where studies have shown that a very significant majority are placed with the thick end down. Your objections are not based on fact but on your refusal to accept the facts.
My Scary Sharpening station is an old marble window sill that was removed from my mom's house when an addition was built. It seems rather flat to me (not measurably off by my crude measurements and certainly not off enough to rock a plane or a blade). It is about 3 feet or so long and wide enough for a sanding belt. Can set up a whole range of grits from 80 to 2000 in small sheets at one time. When done, it stands in a corner somewhere. Probably can find one somewhere where a building is coming down or something.
Very interesting, but as the author pointed out, he is talking about stained glass in cathedrals. I also note that he says that a researcher found about half of the pieces of glass in windows were thicker on the top. I already argued that a worker couldn't possibly have determined the thick end and consistently placed that end on the bottom. It is interesting that other use the thick on the bottom for proof of glass flow and others argue it is thick because the worker placed it that way. Guess both arguments are bullshit, which is what I said.
You have to know what the thickness was at the beginning of the period and the end of the period, regardless of whether the top or the bottom is the thickest. No one has provided that information.
I don't if the flow idea from cathedral windows is valid or not, most likely invalid. That doesn't mean that there isn't evidence in lime glass. But, if it flows it certainly moves very slowly. Does it flow with pressure?
I wonder if Brill ever examined the aging of broken glass edges with an electron microscope?
BTW, someone questioned the validity of the supercooled liquid idea and wanted an authority. How about Linus Pauling? Good enough?
I'm finished. If you find something definitive (valid scientific tests that have been repeated by several scientist) let me know. BTW, experiments using current measurement techniques should easily prove whether glass (softer kinds) actually flow over time. The rest is just blather. Brill's arguments on viscosity are rather weak and trivial. Why not just do the experiments and provide the data on thickness over time.
On Tue, 4 Oct 2005 09:44:37 -0700, with neither quill nor qualm, "Charles Spitzer" quickly quoth:
As I said, I thoroughly cleaned the thing, then inspected it carefully. Sure enough, it was a scratch. Of that I have absolutely no doubt. It caught my fingernail and had a gritty sound when it did. But it was gone at a later date. I'm convinced that some formulations of glass do heal. Oh, I also looked for some sort of coating on the glass and found none. It "ticked" when I tapped it with my fingernail. I'm still tickled that it fixed itself. BTW, I've been sober for 20 years straight now, so I wasn't liquidly mistaken. ;)
-------------------------------------------------------- Murphy was an Optimist ----------------------------
From my original message ... "The underlying surface is flat".
Thanks for the vote of confidence. Is this where I say, "you'd think they read the original post." and you reply, "Ass-me. No, I'd not expect that" :)
Just to clarify, I measured it on my table saw top, my 8" jointer, and my workbench ... all of which have been checked for flatness. But the real indicator is that if the piece is flipped over, the bow likewise switches from facing top to facing bottom.
I've got a monster 4' x 3' sheet mounted to 5/4 birch ply and stiffened w/ steel. I don't bother pulling it out unless I'm lapping the sole of a bench plane or a slick. I've found the outfeed table of my jointer works really well.
It doesn't claim that glass is always laid that way. Just that it's done SOME times, and I'm sure the urban myth wasn't started by someone using a micrometer. Since there is no evidence of glass flowing, that theory explains why some houses DO have "thicker at the bottom" glass better than any other theory.
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