Jennifer Buckner on tue 14 dec 04
Here are three articles on the properties of glass, all of them refuting
the generally accepted myth that glass is a liquid.
Jennifer Buckner
Jennifer G. Buckner jenniverre@earthlink.net
Ditmar on tue 14 dec 04
An urban myth / old wives tale.
Many of the old glass panels had thicker areas due to how they were
manufactured.
Blown, opened and spun into a disc several feet across. Invariably the outer
edges were thinner, getting thicker as you move towards the center of the
disc. The square panes were cut and most commonly mounted with the thicker
edge to the bottom.
Ditmar
> I have visited the Peter Wentz Farmstead(1760's) in Montgomery Co, PA.
> I have seen handblown (presumably lead glass) window panes which have
> sagged considerably in the intervening 240 years, and are demonstrably
> thicker at the bottom. I have also seen this in France in old
> buildings.
>
> >
Leaded glass in a church or an old New
> > England farmhouse could "sag" as a result of repeated
> > exposure to the sunrays."
> >
> >
> > Any opinions on this ?
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Diane Winters on tue 14 dec 04
I've got a set of liqueur glasses made in the 1970's in what's now the Czech
Republic. They are thin glass, perfectly vertical cylinders
(straight-sided) sitting up on stems. They've now got fine horizontal
ridges in the walls, faint but easily seen with the naked eye in decent
light, from periodic successive "slumps." They were definitely not like
that when I bought them - became noticible after about 15 years. At first I
was disappointed, then decided I liked the fact that the material was just
behaving according to its own inherent rules.
I wonder if it depends on the type of glass and how it was formed. These
were supposedly crystal, so that may be a factor. Maybe a thick lead glaze
on a vase might do something similar if it didn't have the pottery to hold
it up.
Diane
in Oakland/Berkeley where my Open Studios sales so far are better than last
year's (not so very hard to do). Still another week and a half to go.
Jennifer Boyer on tue 14 dec 04
OK,
Here goes:
I was reading Bill Bryson's "Short History of Nearly Everything" and he
said the following talking about the properties of rocks of the
aesthenosphere in the earth's crust:
"Similarly it is misleading to rocks flowing in anything like the way
we think of materials flowing in the surface. THe rocks are viscous,
but only in the same way that glass is. It may not look it but all the
glass on Earth is flowing downward under the relentless drag of
gravity. Remove a pane of really old glass from the window of a
European cathedral and it will be thicker at the bottom than at the
top. That is the sort of flow we are talking about. The hour hand on a
clock moves about 10,000 times faster than the "flowing rocks of the
mantle."
I told this theory to friends at the local coffee shop and met with
scepticism about the cathedral glass. I went on the internet and found
a bunch of web sites debunking the idea that glass can change shape at
room temp over time. Here's a typical debunk:
"Glass and the glassy state are often described by noting their
similarities with liquids. So good teachers, such as Mr. Hoke was, like
to quote the story about the windows. As is the case with liquids, the
atoms making up a glass are not arranged in any regular order-and that
is where the analogy arises. Liquids flow because there are no strong
forces holding their molecules together. Their molecules can move
freely past one another, so that liquids can be poured, splashed
around, and spilled. But, unlike the molecules in conventional liquids,
the atoms in glasses are all held together tightly by strong chemical
bonds. It is as if the glass were one giant molecule. This makes
glasses rigid so they cannot flow at room temperatures. Thus, the
analogy fails in the case of fluidity and flow."
Then a friend emailed me this:
"I called my cousin the
glassblower. While he might technically agree with the
statement that "solid glass doesn't sag," he tells me
that "fluxing" can give glass this property. "Flux" is
an agent like lead or lime that is commonly added to
glass to reduce the temperature at which it will
liquefy (from around 1,100 degrees to around 400
degrees). Leaded glass in a church or an old New
England farmhouse could "sag" as a result of repeated
exposure to the sunrays."
Any opinions on this ?
Jennifer
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Cindy on tue 14 dec 04
Hi, Jennifer
I don't know whether the scientifically correct word is "flow" or "sag" or
something else, I can tell you that the very old windows in my home are
thicker at the bottoms. I'm pretty sure they didn't come from the 5&Dime
that way.
Merry Christmas
Cindy in SD
----- Original Message -----
From: "Jennifer Boyer"
To:
Sent: Tuesday, December 14, 2004 1:58 PM
Subject: Can glass move/sag over time?
> OK,
> Here goes:
> I was reading Bill Bryson's "Short History of Nearly Everything" and he
> said the following talking about the properties of rocks of the
> aesthenosphere in the earth's crust:
>
> "Similarly it is misleading to rocks flowing in anything like the way
> we think of materials flowing in the surface. THe rocks are viscous,
> but only in the same way that glass is. It may not look it but all the
> glass on Earth is flowing downward under the relentless drag of
> gravity. Remove a pane of really old glass from the window of a
> European cathedral and it will be thicker at the bottom than at the
> top. That is the sort of flow we are talking about. The hour hand on a
> clock moves about 10,000 times faster than the "flowing rocks of the
> mantle."
>
> I told this theory to friends at the local coffee shop and met with
> scepticism about the cathedral glass. I went on the internet and found
> a bunch of web sites debunking the idea that glass can change shape at
> room temp over time. Here's a typical debunk:
>
> "Glass and the glassy state are often described by noting their
> similarities with liquids. So good teachers, such as Mr. Hoke was, like
> to quote the story about the windows. As is the case with liquids, the
> atoms making up a glass are not arranged in any regular order-and that
> is where the analogy arises. Liquids flow because there are no strong
> forces holding their molecules together. Their molecules can move
> freely past one another, so that liquids can be poured, splashed
> around, and spilled. But, unlike the molecules in conventional liquids,
> the atoms in glasses are all held together tightly by strong chemical
> bonds. It is as if the glass were one giant molecule. This makes
> glasses rigid so they cannot flow at room temperatures. Thus, the
> analogy fails in the case of fluidity and flow."
>
> Then a friend emailed me this:
>
> "I called my cousin the
> glassblower. While he might technically agree with the
> statement that "solid glass doesn't sag," he tells me
> that "fluxing" can give glass this property. "Flux" is
> an agent like lead or lime that is commonly added to
> glass to reduce the temperature at which it will
> liquefy (from around 1,100 degrees to around 400
> degrees). Leaded glass in a church or an old New
> England farmhouse could "sag" as a result of repeated
> exposure to the sunrays."
>
>
> Any opinions on this ?
>
> Jennifer
>
> ************************
> Jennifer Boyer
> Thistle Hill Pottery
> Montpelier, VT
>
> http://thistlehillpottery.com
>
>
____________________________________________________________________________
__
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
>
Hank Murrow on tue 14 dec 04
Dear Jennifer;
I have visited the Peter Wentz Farmstead(1760's) in Montgomery Co, PA.
I have seen handblown (presumably lead glass) window panes which have
sagged considerably in the intervening 240 years, and are demonstrably
thicker at the bottom. I have also seen this in France in old
buildings.
Cheers from Eugene, Hank
www.murrow.biz/hank
On Dec 14, 2004, at 12:58 PM, Jennifer Boyer wrote:
>
> I was reading Bill Bryson's "Short History of Nearly Everything" and he
> said the following talking about the properties of rocks of the
> aesthenosphere in the earth's crust:
>
> "Similarly it is misleading to rocks flowing in anything like the way
> we think of materials flowing in the surface. THe rocks are viscous,
> but only in the same way that glass is. It may not look it but all the
> glass on Earth is flowing downward under the relentless drag of
> gravity. Remove a pane of really old glass from the window of a
> European cathedral and it will be thicker at the bottom than at the
> top. That is the sort of flow we are talking about. The hour hand on a
> clock moves about 10,000 times faster than the "flowing rocks of the
> mantle."
>
> I told this theory to friends at the local coffee shop and met with
> scepticism about the cathedral glass. I went on the internet and found
> a bunch of web sites debunking the idea that glass can change shape at
> room temp over time. Here's a typical debunk:
>
> "Glass and the glassy state are often described by noting their
> similarities with liquids. So good teachers, such as Mr. Hoke was, like
> to quote the story about the windows. As is the case with liquids, the
> atoms making up a glass are not arranged in any regular order-and that
> is where the analogy arises. Liquids flow because there are no strong
> forces holding their molecules together. Their molecules can move
> freely past one another, so that liquids can be poured, splashed
> around, and spilled. But, unlike the molecules in conventional liquids,
> the atoms in glasses are all held together tightly by strong chemical
> bonds. It is as if the glass were one giant molecule. This makes
> glasses rigid so they cannot flow at room temperatures. Thus, the
> analogy fails in the case of fluidity and flow."
>
> Then a friend emailed me this:
>
> "I called my cousin the
> glassblower. While he might technically agree with the
> statement that "solid glass doesn't sag," he tells me
> that "fluxing" can give glass this property. "Flux" is
> an agent like lead or lime that is commonly added to
> glass to reduce the temperature at which it will
> liquefy (from around 1,100 degrees to around 400
> degrees). Leaded glass in a church or an old New
> England farmhouse could "sag" as a result of repeated
> exposure to the sunrays."
>
>
> Any opinions on this ?
wjskw@BELLSOUTH.NET on wed 15 dec 04
Jennifer:
I have seen this firsthand in windows of some older homes on Cape
Cod. Glass does "flow" over time. Usually hundreds of years.
Actually measurable thickening at the bottoms of the panes.
Guess we all better leave a bit of room at the bottom of our pots
for the future generations
Wayne Seidl
a very cold 52F (13C) with a 30 knot wind here this morning
in Key West FL BRRR!
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of
Jennifer Boyer
Sent: Tuesday, December 14, 2004 3:58 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Can glass move/sag over time?
OK,
Here goes:
I was reading Bill Bryson's "Short History of Nearly Everything" and
he
said the following talking about the properties of rocks of the
aesthenosphere in the earth's crust:
"Similarly it is misleading to rocks flowing in anything like the
way
we think of materials flowing in the surface. THe rocks are viscous,
but only in the same way that glass is. It may not look it but all
the
glass on Earth is flowing downward under the relentless drag of
gravity. Remove a pane of really old glass from the window of a
European cathedral and it will be thicker at the bottom than at the
top. That is the sort of flow we are talking about. The hour hand on
a
clock moves about 10,000 times faster than the "flowing rocks of the
mantle."
I told this theory to friends at the local coffee shop and met with
scepticism about the cathedral glass. I went on the internet and
found
a bunch of web sites debunking the idea that glass can change shape
at
room temp over time. Here's a typical debunk:
"Glass and the glassy state are often described by noting their
similarities with liquids. So good teachers, such as Mr. Hoke was,
like
to quote the story about the windows. As is the case with liquids,
the
atoms making up a glass are not arranged in any regular order-and
that
is where the analogy arises. Liquids flow because there are no
strong
forces holding their molecules together. Their molecules can move
freely past one another, so that liquids can be poured, splashed
around, and spilled. But, unlike the molecules in conventional
liquids,
the atoms in glasses are all held together tightly by strong
chemical
bonds. It is as if the glass were one giant molecule. This makes
glasses rigid so they cannot flow at room temperatures. Thus, the
analogy fails in the case of fluidity and flow."
Then a friend emailed me this:
"I called my cousin the
glassblower. While he might technically agree with the
statement that "solid glass doesn't sag," he tells me
that "fluxing" can give glass this property. "Flux" is
an agent like lead or lime that is commonly added to
glass to reduce the temperature at which it will
liquefy (from around 1,100 degrees to around 400
degrees). Leaded glass in a church or an old New
England farmhouse could "sag" as a result of repeated
exposure to the sunrays."
Any opinions on this ?
Jennifer
Tig Dupre on wed 15 dec 04
Jennifer,
My research chemist brother tells me that glass is technically defined as a super-cooled silicaceous liquid. It flows, but *VERY* slowly.
Test: carefully remove a pane of glass from an old (50 years) window frame, after marking which is top and which is bottom. Measure the thickness at the top edge, then the bottom edge. The bottom will be thicker.
No, it will not be remarkably pear-shaped, or noticeably wedge-shaped, but still thicker.
I would think that suspending a square pane of glass by four corners, mounting it on small pedestals, would sag the glass in the middle over time. You could speed up the process by placing a weight in the middle. Perhaps a small anvil might do? :o)
For what it's worth, there's your answer,
Tig Dupre
in Port Orchard, Washington, USA
Bob Masta on wed 15 dec 04
Regarding the observation that old window panes are thicker
at the bottom, I've read that this is because they were made
before the invention of float glass, so they typically were
uneven to start with. The installers naturally put the heavy
side down.
Best regards,
Bob Masta
potsATdaqartaDOTcom
Hank Murrow on wed 15 dec 04
On Dec 14, 2004, at 5:41 PM, Hank Murrow wrote:
>
> I have visited the Peter Wentz Farmstead(1760's) in Montgomery Co, PA.
> I have seen handblown (presumably lead glass) window panes which have
> sagged considerably in the intervening 240 years, and are demonstrably
> thicker at the bottom. I have also seen this in France in old
> buildings.
I have been corrected by Lee's post and also Clifton Webb's private
post. Apparently, the glass, uneven at manufacture, was installed with
the thicker side down to start with.
Cheers, Hank in Eugene....... opening another firing today........ what
will ClaySanta bring?
www.murrow.biz/hank
Steve Mills on wed 15 dec 04
My understanding is that technically speaking Glass is classified as a
liquid. So it follows that it *flows*.
Steve
Bath
UK
In message , Cindy writes
>Hi, Jennifer
>
>I don't know whether the scientifically correct word is "flow" or "sag" o=
>r
>something else, I can tell you that the very old windows in my home are
>thicker at the bottoms. I'm pretty sure they didn't come from the 5&Dime
>that way.
>
>Merry Christmas
>Cindy in SD
>
--
Steve Mills
Bath
UK
Greg Marshall on wed 15 dec 04
Jennifer,
The timing on your question about "can glass move or sag over time" was
very good. We get Earth and Sky on our local public radio station. On the
Tuesday, Dec. 14, show the topic was "Vocanoes - The Original Glass
Makers". In the report, they state that "it is a myth that glass sags due
to its liquid quality". Check out their website at www.earthsky.com and
under "Also This Week" click on "Volcanoes-The Original Glass Makers" for
their complete report.
Greg at the foot of Pikes Peak.
Ivor and Olive Lewis on wed 15 dec 04
Dear Jennifer Boyer,
Regarding the flow of glass at ambient temperatures.....You will need
to research this because it may be an urban legend but....
After York Minster was burned some years ago many of the old windows
were destroyed by the heat of the fire. Someone thought to measure the
thickness of some of the glass shards when they were piecing together
the jigsaw of fragments. They found that splinters from the upper
parts of some of the panes were much thinner than the lower parts from
the same panes of glass. This, it has been claimed, demonstrates that
glass has fluidic properties at ordinary temperatures.
Given that the crust of the Earth heats up as you go deeper it is
possible to calculate the depth at which silicate rocks behave as
fluids. Where this happens is called the Mohorovicic discontinuity and
it exists at a depth of about 10 km below the floor of the ocean
basins and about 35 km below the continental plates. The fact that
certain earthquake waves are not transmitted through this feature
leads to the assumption that it is a fluid medium
A key word to search for is "Creep". Relating to interatomic forces,
the Writings of Prof. Linus Pauling might be a good place to start.
Interesting topic.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Jennifer Boyer on wed 15 dec 04
Thanks everyone: I got more than enough info to gnaw on. Seems like the
sagging glass thing is a myth.... Makes sense that they would install
uneven panes of glass with the heavy side down.
But I wonder what's with Diane's glasses that have developed ridges!?
Jennifer
On Dec 15, 2004, at 12:36 PM, Greg Marshall wrote:
> Jennifer,
>
> The timing on your question about "can glass move or sag over time" was
> very good. We get Earth and Sky on our local public radio station.
> On the
> Tuesday, Dec. 14, show the topic was "Vocanoes - The Original Glass
> Makers". In the report, they state that "it is a myth that glass sags
> due
> to its liquid quality". Check out their website at www.earthsky.com
> and
> under "Also This Week" click on "Volcanoes-The Original Glass Makers"
> for
> their complete report.
>
> Greg at the foot of Pikes Peak.
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Jennifer Boyer on wed 15 dec 04
So Ivor,
What about the idea that most window glass was uneven because of the
primitive manufacturing process of the time, and panes were installed
thick side down?
Jennifer
On Dec 14, 2004, at 10:30 PM, Ivor and Olive Lewis wrote:
> Dear Jennifer Boyer,
>
> Regarding the flow of glass at ambient temperatures.....You will need
> to research this because it may be an urban legend but....
> After York Minster was burned some years ago many of the old windows
> were destroyed by the heat of the fire. Someone thought to measure the
> thickness of some of the glass shards when they were piecing together
> the jigsaw of fragments. They found that splinters from the upper
> parts of some of the panes were much thinner than the lower parts from
> the same panes of glass. This, it has been claimed, demonstrates that
> glass has fluidic properties at ordinary temperatures.
> Given that the crust of the Earth heats up as you go deeper it is
> possible to calculate the depth at which silicate rocks behave as
> fluids. Where this happens is called the Mohorovicic discontinuity and
> it exists at a depth of about 10 km below the floor of the ocean
> basins and about 35 km below the continental plates. The fact that
> certain earthquake waves are not transmitted through this feature
> leads to the assumption that it is a fluid medium
> A key word to search for is "Creep". Relating to interatomic forces,
> the Writings of Prof. Linus Pauling might be a good place to start.
> Interesting topic.
> Best regards,
> Ivor Lewis.
> Redhill,
> S. Australia.
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Lee Love on wed 15 dec 04
Jennifer Boyer wrote:
> top. That is the sort of flow we are talking about. The hour hand on a
> clock moves about 10,000 times faster than the "flowing rocks of the
> mantle."
I found the same stuff on the web Jennifer:
> Yvonne Stokes has calculated how long would be long enough. Assuming a
> windowpane simply flows downhill, she asked, how long would it take
> for the bottom to get just 5 percent thicker? At least 10 million
> years, she figures--and that is likely to be a "big underestimate."
> Cathedral windows may be thicker at the bottom, she says, simply
> because handmade glass varies in thickness, and medieval builders
> chose to put the thick ends down. And wavy old windowpanes are not
> glass that has flowed; they're glass that was flawed from the beginning.
Fulll article:
http://www.findarticles.com/p/articles/mi_m1511/is_10_20/ai_55926971
--
Lee in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
Ivor and Olive Lewis on thu 16 dec 04
As I said in my reply,
The window glass evidence for flow in cold glass might be an urban
legend but "Creep" is a well known material phenomenon that can be
measured in materials under stress.
Best regards,Ivor Lewis.
Redhill,
S. Australia.
Sarah House on thu 16 dec 04
this was mentioned on one of the NPR short segments yesterday, i think
it was Earth and Sky. They confirmed what I had found out after asking
the same question a few years ago. Glass is considered a "Super Cooled
Liquid" it looks and feels like a solid, but it's molecules still behave
like a liquid. But it doesn't move except under extreme tempretures,
(think kiln) The wavy melted look in old glass is a result of the
forming process. The old house I lived in had all the wavy parts going
in different directions, some look like they had melted up.
Sarah House
http://www.skhpottery.com
In Little Switzerland, NC
soon to be
In Burnsville, NC
Robert Seele on thu 16 dec 04
On Wednesday, December 15, 2004, at 06:50 PM, Jennifer Boyer wrote:
> What about the idea that most window glass was uneven because of the
> primitive manufacturing process of the time, and panes were installed
> thick side down?
I don't think the people were careful enough or cared all that much as
to which way a pane of glass was put into the sash. I know I never
checked.
Bob Seele
If you find yourself in a hole, stop digging...Will Rogers
Ivor and Olive Lewis on thu 16 dec 04
Dear Jennifer Boyer,
Glass has been around for a long time. Having worked for a short
period of time at James A. Joblings Pyrex glassworks I think that
glass blowing was a highly sophisticated exercise many centuries ago.
One method was to blow a large bubble of glass, shape this into a bowl
then spin it into a large disc which was cut into useable panes
My 3D Lecturer at Sunderland College, Charles Bray, has written what
might be called a companion to the famous Hamer's dictionary called
"Dictionary of Glass. Materials and Techniques" ISBN 976-6910-89-5.
There is and extensive entry on "Sheet Glass". See entries
for"Bullion" and "Crown". Minor faults caused by inadequate mixing of
the melt caused "Striations" or surface imperfections and bubbles.
There are two fundamental inventions which changed the quality of
glass. One was the introduction of "Fining", the addition of chemicals
that caused the removal of gas as well as impurities and "Float Glass"
which is extremely uniform in thickness and can be made at high speed.
People who would like to know more about glass should try to lay their
hands on Charles Bray's Book.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Diane Winters on thu 16 dec 04
Jennifer wrote:
> Seems like thesagging glass thing is a myth.... Makes sense that
> they would install uneven panes of glass with the heavy side down.
> But I wonder what's with Diane's glasses that have developed > =
ridges!?
OK, I've got a theory, cockeyed enough to be hesitant posting it =
publicly
for fear of being laughed out of Claytown.
On the one hand, the websites trouncing the slumping of glass as a myth =
seem
sound and knowledgeable about glass. On the other hand, I find it hard =
to
imagine a worldwide and historically persistent "professional practice"
among glaziers to always install glass with the thicker side downward.
So...
When I posted my message, I began to wonder what constitutes crystal, =
and it
turns out it's merely the presence of lead oxide in place of the calcium
oxide used in plain glass. Usually it's anywhere from 8 - 24%, but
Swarovsky beads have 32% lead Lead is added for brightness and clarity. =
I
wonder if it's such additives that cause the glass involved to behave
differently from "pure glass", lead oxide being a good old low-fire flux =
and
all. Also wonder if anyone has checked very old window glass for lead
content.
Now, go ahead and laugh.....
Diane in Oakland/Berkeley where very few windows are more
than 150 years old, and most a lot less
Jennifer Boyer on thu 16 dec 04
Well, Your idea is shared by my friend's glass blowing cousin:
" I called my cousin the
glassblower. While he might technically agree with the
statement that "solid glass doesn't sag," he tells me
that "fluxing" can give glass this property. "Flux" is
an agent like lead or lime that is commonly added to
glass to reduce the temperature at which it will
liquefy (from around 1,100 degrees to around 400
degrees). Leaded glass in a church or an old New
England farmhouse could "sag" as a result of repeated
exposure to the sunrays."
hmmm.....
Jennifer, thinking of pestering some other glass blowing friends....
On Dec 16, 2004, at 8:11 PM, Diane Winters wrote:
> Jennifer wrote:
>> Seems like thesagging glass thing is a myth.... Makes sense that
>> they would install uneven panes of glass with the heavy side down.
>> But I wonder what's with Diane's glasses that have developed > =
> ridges!?
>
>
>
> OK, I've got a theory, cockeyed enough to be hesitant posting it =
> publicly
> for fear of being laughed out of Claytown.
>
> On the one hand, the websites trouncing the slumping of glass as a
> myth =
> seem
> sound and knowledgeable about glass. On the other hand, I find it
> hard =
> to
> imagine a worldwide and historically persistent "professional practice"
> among glaziers to always install glass with the thicker side downward.
> So...
>
> When I posted my message, I began to wonder what constitutes crystal, =
> and it
> turns out it's merely the presence of lead oxide in place of the
> calcium
> oxide used in plain glass. Usually it's anywhere from 8 - 24%, but
> Swarovsky beads have 32% lead Lead is added for brightness and
> clarity. =
> I
> wonder if it's such additives that cause the glass involved to behave
> differently from "pure glass", lead oxide being a good old low-fire
> flux =
> and
> all. Also wonder if anyone has checked very old window glass for lead
> content.
>
> Now, go ahead and laugh.....
>
> Diane in Oakland/Berkeley where very few windows are more
> than 150 years old, and most a lot less
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
Ivor and Olive Lewis on fri 17 dec 04
Dear Bob Masta,
Crown Glass, that made by blowing then spinning to make a large
circular sheet, would have had differing thicknesses at each corner.
This becomes obvious when you look at the cutting plans used to
maximise the useful area and reduce waste.
Best regards
Ivor Lewis.
Redhill,
S. Australia.
pdp1@EARTHLINK.NET on fri 17 dec 04
Hi Ivor,
Nice mention...
Given that the cutting schedules for those discs of Crown
Glass, tended to have the subsequent cut-outs of squares or
rectangles being thickest at their one corner and thinnest
at the opposite corner...and other methods, which ground the
Sheets to uniform thickness left all sides about what anyone
would call of 'even' thickness...or if varying, did vary not
by much...
...seems to leaves us ( I think) still savoring the mystery
of
how-it-is then...that Old Windows, even those of the early
and not-so-early
20th Century that were of the most common sort of everyday
Windows, may be
discovered to
have panes whose bottom chords are (evenly
along-their-width,)
uniformly
thicker than their evenly-along-their-widths of less-thick
tops.
Can we identify the method of Glass Manufacture, whose
subsequent sheets should thence have been so cut up by (de
jur or other) Glaziers, as
to
result in panes being ( supposedly) so unerringly installed
with their 'thick-edges' (that is, even as say 8 or 10
thousandths thicker even) allways 'down'?
Does the plot thicken?
Happy Hollidays all...
& Work days too...
Phil
el ve
----- Original Message -----
From: "Ivor and Olive Lewis"
> Dear Bob Masta,
> Crown Glass, that made by blowing then spinning to make a
large
> circular sheet, would have had differing thicknesses at
each corner.
> This becomes obvious when you look at the cutting plans
used to
> maximise the useful area and reduce waste.
> Best regards
> Ivor Lewis.
> Redhill,
> S. Australia.
Lee Love on fri 17 dec 04
Diane Winters wrote:
>OK, I've got a theory, cockeyed enough to be hesitant posting it publicly
>for fear of being laughed out of Claytown.
>
Jennifer Boyer wrote:
> "Flux" is an agent like lead or lime that is commonly added to
> glass to reduce the temperature at which it will liquefy
Hey guys, please read the articles below (Jennifer, you can print out a
PDF of the second one for your cousin.)
Lead, itself does not flow (the lead that holds the cathedral stained
glass in place), even though it is about a billion times more fluid than
glass. As one person says in an article below, if glass did move
like some folks think cathedral glass does, all the Egyptian glass would
just be "puddles in their tombs." ;-)
If you look at the articles on the web, you will note that some of the
"cathedral" glass can be found with the thick part of the glass at the
top. (some apprentice didn't follow the master's instructions to put
the thick part at the bottom.) ;-)
These are a couple of the best articles by people who should know better:
written by Robert C. Plumb Worcester Polytechnic Institute, Worcester,
MA 01609
http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/windowpane.html
written by Dr. Robert Brill, Research Scientist at the Corning Museum of
Glass:
http://www.glassnotes.com/WindowPanes.html
-
in Mashiko, Japan http://mashiko.org
http://www.livejournal.com/users/togeika/ WEB LOG
http://public.fotki.com/togeika/ Photos!
Ditmar on fri 17 dec 04
The lead itself does deform. Its a cause of many stained glass panel
failures and repair work. Stiffening ribs of brass, zinc etc, are used to
keep panels more rigid. It's why you don't see leaded panels mounted
overhead (flat) unless proper safety precautions are in place.
Ditmar
> Lead, itself does not flow (the lead that holds the cathedral stained
> glass in place), even though it is about a billion times more fluid than
> glass. As one person says in an article below, if glass did move
> like some folks think cathedral glass does, all the Egyptian glass would
> just be "puddles in their tombs." ;-)
>>
http://dwb.unl.edu/Teacher/NSF/C01/C01Links/www.ualberta.ca/~bderksen/window
pane.html
>
> written by Dr. Robert Brill, Research Scientist at the Corning Museum of
> Glass:
>
> http://www.glassnotes.com/WindowPanes.html
>
> -
> in Mashiko, Japan http://mashiko.org
> http://www.livejournal.com/users/togeika/ WEB LOG
> http://public.fotki.com/togeika/ Photos!
>
>
____________________________________________________________________________
__
>
Ivor and Olive Lewis on fri 17 dec 04
Dear Jennifer Boyer,
Ron Roy is the one who could give us some definitive information about
the temperature at which a glass could become mobile by using his
dilatometer. I think 400=BA C is a bit on the low side. Laboratory
tubing seems to melt at a low red heat, with the colour just becoming
visible.
But I am still of the opinion that any movement, change in length,
would be due to "Creep" and not because glass is a "supercooled
fluid".
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Ivor and Olive Lewis on fri 17 dec 04
Dear Diane Winters,
I think you would need to do some deep research to get to an answer. I
can see your argument. Lead glasses have lower melting points than
soda calcia glasses and also a greater relative density so they would
be more prone to slump. Pretty logical sense to me. But Soda glass has
an equally, if not longer, history
But I think you will find Swarovski increase the lead content in their
decorative glass to enhance its dispersive power, its ability to give
rainbow flashes.
Lead glass has been around since Roman times.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Cecilia Wian on fri 17 dec 04
>I am with Phil in Vegas on this! Do not let them fool you about having
>"explained" an "urban myth"... The subject came up once before with the
>same split in opinion between believers and non-believers. And I have seen
>nothing in the interim to change my mind.
>
> Sincerely
>
> Janet Kaiser
and.... does it really matter anyway which side is "right"? Is this
affecting someone's work?
Cecilia - wondering why this is even a discussion *grin*
Ivor and Olive Lewis on sat 18 dec 04
Dear Phil,
So far there has been no evidence presented in this discussion. NO
before and after values. NO records of time elapsed. NO date of
manufacture. ALL hearsay.
Get hold of a copy of Charles Bray's Book. Fair enough, he only give a
brief summary of manufacturing methods but it is interesting to read.
We forget that artisans have been grinding glass for a couple of
millennia, that Plate Glass, ground to have parallel faces was used
for mirrors and in furniture. When was Versailles built?
No one has taken up the idea that I gave about "Creep". My old boss,
Dr Jim Cairney had about forty Creep Machines in the basement lab to
test experimental turbine blade steel samples. I do have values for
the Creep of glass but they are at elevated temperatures.
I doubt the assumption that glass is a supercooled fluid. Density
variation between crystalline and fused quartz do not, in my opinion,
support the Zachariasen molecular Model of a generalised Glass
Structure.
Said my piece on this one.
Best regards,
Ivor.
Ivor and Olive Lewis on sat 18 dec 04
I think there is some confusion here. Back to the old problem of
speaking in "contractions" Perhaps "Lead" means Lead Sesquisilicate or
Lead Monoxide or one of the other substances incorporated in a glass
recipe batch.
Metallic lead has the wonderful property of "Self Annealing". Like
most metallic elements it hardens when worked by hammering, rolling,
drawing or extruding. but left to sit undisturbed at room temperature
is slowly softens again. No need to keep reheating it as you do a
piece of forged steel.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
Janet Kaiser on sat 18 dec 04
I am with Phil in Vegas on this! Do not let them fool you about
having "explained" an "urban myth"... The subject came up once
before with the same split in opinion between believers and
non-believers. And I have seen nothing in the interim to change
my mind.
Sincerely
Janet Kaiser
Ugandan saying of the day:
"She who wants all, tells the others to be contented"
*** IN REPLY TO THE FOLLOWING MAIL:
>Hi Hank, all...
>Don't let 'em bamboozle ya...
>And don't let 'em fool ya...
*** THE MAIL FROM pdp1@EARTHLINK.NET ENDS HERE ***
***********************************************************
The Chapel of Art : Capel Celfyddyd
8 Marine Crescent : Criccieth : Wales : UK
Home of The International Potters' Path
Tel: ++44 (01766) 523570 http://www.the-coa.org.uk
************* Virus Protection by AVG *****************
************************************************************
pdp1@EARTHLINK.NET on sat 18 dec 04
Hi Ivor,
Oooooo...ouch...
Please...bear with me?
It's all for fun...
And - my own sense of this, in
summary...has been, and remains...simply, innocently, good
naturedly...that:
Cathedral or other old Stained Glass, Sash or Lead or other
Came-held of small irregular or other paned Windows...were
likely never assembled with any consistancy of their pieces
being placed ultimately with any so-called
'thick-edge-down'.
Tudor 'Diamond' panes likely were accorded some consistancy
as for their vagueries being disposed about the same, but
not in the Colored-textured-whirled Glass of the otherwise
"Church' or kindred kind various shapes of little panes of
Windows.
Where, the governing logic of use for these kinds of Glass
pieces would
have been however the Window makers, or Glass Cutting and
Came assembleing Artisans, got the shapes and sizes they
needed, in whatever orientations they could, from whatever
diminishing choices of the larger initial tongues or
sections (and their
breakages in transport or other) or as the small
sheets they had to work with, allowed....and to use it up
and make 'do'.
Hear-say having been that of 'Old' Windows (otherwise, or at
all) end up over time,
being thickest at their bottom chords or edges...does not
seem to
co-respond with any known means of sheet glass production in
any period of history, from which, especially square or
rectangular panes could have routinely
resulted having one edge thickest. One 'corner' thickest,
yes...one long edge, no...at least not that any of us have
discovered so far from a survey of Manufacturing methods and
probable cutting schedules from which individual panes would
be cut from larger initial discs, sheets or other initial
'parent' forms.
From a disc, one may get half of one's largest panes with a
square orientation and half with a diamond orientation it
seems to me. So far as perimiter-to-center area is
concerned, which is where, one way or the other, some
difference in thickness would be expected...
Creep, as I understand it, (and maybe I don't understand it)
is a response to usually some force in excess of the things
itself's poise in gravity's pulling. Otherwise, if Gravity
alone (or some acceleration, anyway) is the agent, it is
'slump'...
I thought it was accepted that Glass can take a transient or
permenent 'set' from 'creep', or that there may be an
elastic rebound either almost instant, or liesured, as
refutes set or creep,
depending on the particulars of the glass itself.
Windows, being held one way or another, in Sash of some
kind, or in frames or in Lead or Copper Came then
in-frames...would not be subject to much of any gross
physical force other than intermittant Wind's pushing on
them, and, the influence of Gravity on their own individual
mass, mitigated by whatever grip on them the grout or puddy
would have to bind them to the Came or Sash or Frame for
their top and side and bottom edges...and
whatever influence Sunlight or Rain may be able to assert
whether such be considered 'phycisal' force or 'Chemical' or
both.
There are and have been many variations and possible
vagueries in any given execution of the recipes and
constituants for the kinds of Glass which could have been or
were used in Windows of various kinds over centuries. Which,
if any sort of Window pane or from-a-sheet-or-disc-abstract
otherwise may
be imagined to have ever ( subtley) 'slumped', it should
stand to reason that some formula-recipe-vaguery would be
liable have such propensity either uniquely, or, in advance
or excess of others.
I recall to have noticed 19 th Century 'Belgian' Plate
Glass Mirrors which had been broken in modern times, appear
to have been very slightly tapered in their thickness
top-to-bottom. I had observed the same thing in conventional
sundry Window panes dating from the 1880s, and, from the
early 1900s ( from when I was re-glazeing various old
Building's Windows) . In retrospect, my sense of the amount
of taper on the 1880s Window panes, would be in the range of
about five to ten thousanths of an inch to the foot of
vertical run. If the Glass came that way, and was installed
that way, then my question was, or is, what means of
manufacture had
produced parent sheets, from which, incidental or casual
Glaziers would have then cut small panes, to end up with
those small panes having such a more or less uniform taper
as was even across their bottom edges? As was not a
'fat-corner', as it were...
The same Building of the 1880s, also has simple flat
'sky-lights' which I thought at the time had the slightest
sag to them...these were about 22 inches by 28 or so, and
some of them were cracked and I replaced them. It was not
any big deal, I did not think to dwell on it or send it to
the
Smithsonian or to the National Labratory of Physics ( where,
we may recall they 'proved' a Mannlicher Carcano round could
pause in mid air, write it's name, come back and dot the
"i"s, and then settle down for a well earned nap on someone
else's [who had nothing to do with any of it's] "stretcher"
in a hallway, and look entirely like a
coy little round fired into Water or Cotton for a routine
Ballistics test, for
all it's previous excertion's 'Toad's Wild Ride' of
travails...)
I did not look at these things critically at the time, but
rather, I merely, casually, peripherally, noticed them.
Can we agree that this is simply an interesting thing to be
curious about?
No?
Yes?
I do not need the facts to be anything one way or the other
here...
But then too, none of us, includeing experts and other
professional institutional occupants of academe, know for
sure, just
what those
facts actually are in all real events which as themselves,
may,
or may not, completely and unerringly respect theory or
anticipations of theory or retrospects of impirical
tendencies attributed to the observed.
Maybe, the kindest mention any of us could summarily make,
is to say that there is the reasoned appearance of a high
order of
anticeedant improbability...for Window pane's "slumping", or
having ever slumped, so far as what the reliable,
demonstratable, earnest
and theoretical knowledge base and investigations of
Science, Physics and Chemistry may sincerely assert.
While...
Science and Physics would never conceed let alone asserted,
that the
Bumble Bee could 'fly'...were it not by sheer unmitigated
fact of Bumble Bees flying quite nicely with no regard to
their opinions about it one way or the other...
And the Bumble Bee was flying already, and continues to do
so...innocently, without feeling obliged to respect their
injunctions against it doing so. So Science and Physics and
Chemistry adjust their cuffs and collars like old Rodney
Dangerfield...and...with some 'ahems', life goes on...
I think that is a good thing to remember.
Or, I am satisfied to hold an open mind on how-it-is
"maybe"...that some sheet Glass, sometimes, according to
it's formula, or vagueries of that formula in practice,
unassayed in retrospect as such, and to the possible effects
of Sunshine or other unassayed electromagnetic or
geomagnetic or other factors which have been
insulted in all quotes from distal experts so
far...may...sometimes...to a degree observable to an unaided
eye, in it's eventuations...'slump'.
And why not?
I feel like some guy in 1931 saying, "You know, I think that
sometimes, here or there, under the right conditions, one
just might see a Coelacanth..."
Then having almost...to duck!
Love,
Phil
el ve
----- Original Message -----
From: "Ivor and Olive Lewis"
> Dear Phil,
> So far there has been no evidence presented in this
discussion. NO
> before and after values. NO records of time elapsed. NO
date of
> manufacture. ALL hearsay.
> Get hold of a copy of Charles Bray's Book. Fair enough, he
only give a
> brief summary of manufacturing methods but it is
interesting to read.
> We forget that artisans have been grinding glass for a
couple of
> millennia, that Plate Glass, ground to have parallel faces
was used
> for mirrors and in furniture. When was Versailles built?
> No one has taken up the idea that I gave about "Creep". My
old boss,
> Dr Jim Cairney had about forty Creep Machines in the
basement lab to
> test experimental turbine blade steel samples. I do have
values for
> the Creep of glass but they are at elevated temperatures.
> I doubt the assumption that glass is a supercooled fluid.
Density
> variation between crystalline and fused quartz do not, in
my opinion,
> support the Zachariasen molecular Model of a generalised
Glass
> Structure.
> Said my piece on this one.
> Best regards,
> Ivor.
Janet Kaiser on sat 18 dec 04
I actually said, "split in opinion".
Nothing about correct or incorrect, right or wrong. Merely
questioning the legitimacy of propounding explanations of
phenomena, by trying to debunk their very existence!
Sincerely
Janet Kaiser -- Definitely lob-sided after a card stuffing
marathon... It has taken a record three days =B0!=B0
*** IN REPLY TO THE FOLLOWING MAIL:
>>I am with Phil in Vegas on this! Do not let them fool you about
having
>>"explained" an "urban myth"... The subject came up once before
with the
>>same split in opinion between believers and non-believers. And
I have seen
>>nothing in the interim to change my mind.
>and.... does it really matter anyway which side is "right"? Is
this
>affecting someone's work?
*** THE MAIL FROM Cecilia Wian ENDS HERE ***
***********************************************************
The Chapel of Art : Capel Celfyddyd
8 Marine Crescent : Criccieth : Wales : UK
Home of The International Potters' Path
Tel: ++44 (01766) 523570 http://www.the-coa.org.uk
************* Virus Protection by AVG *****************
************************************************************
| |
|
