mel jacobson on wed 9 apr 08
this is a totally no/scientific, observation only.
it seems to me that pots fired to vitrification are no
longer iron, but glass.
it is not a metal glaze, it is a glass glaze.
water is what causes heat, not glass.
mel
from minnetonka:
website http://www.visi.com/~melpots/
clayart site:
http://www.visi.com/~melpots/clayart.html
Nobody Special on wed 9 apr 08
On Wed, 9 Apr 2008 07:30:18 -0500, mel jacobson wrote:
>this is a totally no/scientific, observation only.
>
>it seems to me that pots fired to vitrification are no
>longer iron, but glass.
>
>it is not a metal glaze, it is a glass glaze.
>water is what causes heat, not glass.
Mel...
I could very well be completely wrong (the bane of the autodidact), but
isn't the "sparkle" in a kaki glaze caused by iron that has precipitated out
of the melt?
It's my (quite possibly errant) supposition that in a high iron glaze like
Mr. Roy's black liner from MC6G, the glassy matrix, for whatever chemical
reason, is able to incorporate all if the iron into the matrix, binding it
with other elements to make compounds that contain iron, but are no longer
iron (just as table salt is no longer sodium nor chlorine), but in a kaki
(or aventurine) glaze, the glass cannot incorporate all of the iron, so that
some of it precipitates back out. Damn, that's one long paragraph! Sorry!
Hoping for some enlightenment.
...James
Steve Slatin on wed 9 apr 08
James --
I suspect it doesn't make a difference if it's
precipitated from the melt or not. If it's a
part of a glaze, it's suspended, and not
connected physically. To be an antenna,
it has to connect, no?
-- Steve Slatin
Nobody Special wrote:
On Wed, 9 Apr 2008 07:30:18 -0500, mel jacobson wrote:
>this is a totally no/scientific, observation only.
>
>it seems to me that pots fired to vitrification are no
>longer iron, but glass.
>
>it is not a metal glaze, it is a glass glaze.
>water is what causes heat, not glass.
Mel...
I could very well be completely wrong (the bane of the autodidact), but
isn't the "sparkle" in a kaki glaze caused by iron that has precipitated out
of the melt?
It's my (quite possibly errant) supposition that in a high iron glaze like
Mr. Roy's black liner from MC6G, the glassy matrix, for whatever chemical
reason, is able to incorporate all if the iron into the matrix, binding it
with other elements to make compounds that contain iron, but are no longer
iron (just as table salt is no longer sodium nor chlorine), but in a kaki
(or aventurine) glaze, the glass cannot incorporate all of the iron, so that
some of it precipitates back out. Damn, that's one long paragraph! Sorry!
Hoping for some enlightenment.
...James
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Nobody Special on wed 9 apr 08
On Wed, 9 Apr 2008 09:07:52 -0700, Steve Slatin wrote:
>James --
>
> I suspect it doesn't make a difference if it's
> precipitated from the melt or not. If it's a
> part of a glaze, it's suspended, and not
> connected physically. To be an antenna,
> it has to connect, no?
>
> -- Steve Slatin
>
Steve...
I don't think so. From my reading and earlier schooling, I think the
particles only need to be close enough for an electron to make the jump.
Depending on electrical potential, this distance, I understand, need not be
terribly small, and in any case not infinitesimally small.
I believe, freely admitting that it has been approximately 112 years since I
took physics and chemistry, that precipitated iron is metallic iron, and
free to behave as such, but when it is bound up in other compounds it is no
longer iron per se.
Once I get around to boiling my mug, this line of inquiry may quickly become
moot. I find myself hoping that my mug absorbs excessive moisture, but I
don't believe such will be the case. I shall provide an honest answer
either way.
BTW, I enjoy reading your posts, and have done so for several years. Well
reasoned.
All the best.
...James
WILLIAM JAMES on wed 9 apr 08
O.K i gata ask=20
=20
is not glass =3D to glaze
=20
and is not glass an insulator ???
=20
used in all sorts of non conducting stuff??
=20
just a question
=20
joe in blackhawk Co.
nice day went to @#$#% got 2 "'s and more to come
=20
http://joejoejames.spaces.live.com
=20
=20
> Date: Wed, 9 Apr 2008 09:07:52 -0700> From: claystevslat@YAHOO.COM> Subje=
ct: Re: microwave idea> To: CLAYART@LSV.CERAMICS.ORG> > James --> > I suspe=
ct it doesn't make a difference if it's> precipitated from the melt or not.=
If it's a> part of a glaze, it's suspended, and not> connected physically.=
To be an antenna,> it has to connect, no?> > -- Steve Slatin> > Nobody Spe=
cial wrote:> On Wed, 9 Apr 2008 07:30:18 -0500, mel=
jacobson wrote:> > >this is a totally no/scientific, observation only.> >>=
>it seems to me that pots fired to vitrification are no> >longer iron, but=
glass.> >> >it is not a metal glaze, it is a glass glaze.> >water is what =
causes heat, not glass.> > > Mel...> > I could very well be completely wron=
g (the bane of the autodidact), but> isn't the "sparkle" in a kaki glaze ca=
used by iron that has precipitated out> of the melt?> > It's my (quite poss=
ibly errant) supposition that in a high iron glaze like> Mr. Roy's black li=
ner from MC6G, the glassy matrix, for whatever chemical> reason, is able to=
incorporate all if the iron into the matrix, binding it> with other elemen=
ts to make compounds that contain iron, but are no longer> iron (just as ta=
ble salt is no longer sodium nor chlorine), but in a kaki> (or aventurine) =
glaze, the glass cannot incorporate all of the iron, so that> some of it pr=
ecipitates back out. Damn, that's one long paragraph! Sorry!> > Hoping for =
some enlightenment.> > ...James> __________________________________________=
________> Do You Yahoo!?> Tired of spam? Yahoo! Mail has the best spam prot=
ection around> http://mail.yahoo.com> > ___________________________________=
___________________________________________> Clayart members may send posti=
ngs to: clayart@lsv.ceramics.org> > You may look at the archives for the li=
st, post messages, change your> subscription settings or unsubscribe/leave =
the list here: http://www.acers.org/cic/clayart/> > Moderator of the list i=
s Mel Jacobson who may be reached at melpots2@visi.com=
John Sankey on thu 10 apr 08
"precipitated iron is metallic iron"
Not necessarily. For iron to be metallic, there have to be
sufficient iron atoms connected quantum mechanically to produce a
conduction band (overlapping valence bands to chemists). If the
precipitation is colloidal, no metallic state.
I've got a series of test tiles with zero to 35% Fe2O3 in the
kiln as I speak, for my iron studies. When they are done, they're
headed for the microwave...
John Sankey
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John Sankey on thu 10 apr 08
First result from running all my prior 4 dozen test tiles in a microwave.
All tiles were made from the same batch of clay (Tucker Smooth White), all
fired to cone 10, all contain 10% iron. (see http://sankey.ws/glazeiron.html
for details)
Precisely one gets warm, but it's consistent, one with iron, magnesia and
phosphorous but no calcium. It's too hot to touch after only 8 seconds on
high, definitely metallic.
Here's the analysis of it:
molar Seger oxide
0.016 0.060 P2O5
0.599 2.215 SiO2
0.099 0.366 FeO
0.077 0.283 K2O
0.084 0.312 MgO
0.010 0.036 Na2O
0.071 0.262 Al2O3
0.042 0.156 B2O3
Now, to try to figure out how it forms a metallic phase when not a single
one of the others does. And as I mentioned, higher iron tests to come.
John Sankey
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Nobody Special on thu 10 apr 08
On Thu, 10 Apr 2008 08:58:26 -0400, John Sankey wrote:
>First result from running all my prior 4 dozen test tiles in a microwave.
---snip---
>
>Precisely one gets warm, but it's consistent, one with iron, magnesia and
>phosphorous but no calcium. It's too hot to touch after only 8 seconds on
>high, definitely metallic.
---snip---
John...
Very interesting. I was beginning to question my own rationality (no big
deal, everyone else does!).
I feel like Arlo Guthrie, but at least now there are two of us sitting on
the Group W bench...
All the best.
...James
Fredrick Paget on thu 10 apr 08
I have been following the microwave heating discussion and wondering
if an old naging memory from my days as an EE student some 60 years
ago might hold the answer.
There is a property of matter that is known as the dissipation
factor. Its definition is way out there technical and if you are
interested there is a discussion of it on:
[http://www.iza-online.org/synthesis/VS_2ndEd/MicrowaveTech.htm]
Materials with a low dissipation factor such as teflon and glass are
not heated by microwaves whereas those with high factor are heated in
proportion to how high they are. Water is high so we are right that
ceramic with trapped water will be heated. BUT there are a lot of
other materials with high dissipation factor and they are heated too!
In the case of quartz it has been found that contaminants of alkali
metals (lithium, sodium, potassium and magnesium ) can raise the
dissipation factor enough to make it possible to melt the quartz with
microwaves in the manufacture of optical fibers:
[http://www.wipo.int/pctdb/en/wo.jsp?wo=1990013834&IA=WO1990013834&DISPLAY=DESC]
This evidence leads us to the clay body and its constituents and
possible contaminants which can raise the dissipation factor and
cause heating in a microwave oven.
Keep on Googeling, there must be a lot more evidence out there.
--
Fred Paget
Twin Dragon Studio
Mill Valley, CA, USA
fredrick@well.com
Charter Member Potters Council
Jennifer Boyer on fri 11 apr 08
Just to throw my old research into the mix. I did a bunch of kaki
glaze tests at cone 10 awhile ago. Not all of them got hot in the
microwave but SOME did. I actually did an absorption test on my
stoneware clay and ruled out any water absorption. I think Ron may
have helped with that test.
So I'm very interested in this thread, since it seemed to me at the
time that there must be some other variable than iron content in
making a high iron glaze get hot in the microwave.
Jennifer
On Apr 10, 2008, at 7:30 PM, Fredrick Paget wrote:
>
> Materials with a low dissipation factor such as teflon and glass are
> not heated by microwaves whereas those with high factor are heated in
> proportion to how high they are. Water is high so we are right that
> ceramic with trapped water will be heated. BUT there are a lot of
> other materials with high dissipation factor and they are heated too!
>
> In the case of quartz it has been found that contaminants of alkali
> metals (lithium, sodium, potassium and magnesium ) can raise the
> dissipation factor enough to make it possible to melt the quartz with
> microwaves in the manufacture of optical fibers:
> [http://www.wipo.int/pctdb/en/wo.jsp?
> wo=1990013834&IA=WO1990013834&DISPLAY=DESC]
>
>
***************************
Jennifer Boyer
Thistle Hill Pottery
Montpelier, VT
http://thistlehillpottery.com
http://jboyerdesign.com
http://artisanshand.com
***************************
John Sankey on fri 11 apr 08
"There is a property of matter that is known as the dissipation
factor."
This is a measurement of the total of all effects of alternating
fields on a material. Measurements such as dissipation factor
are a quick guide to a territory, but at one frequency, it
doesn't have anything to say about what causes the interaction.
Dipole moments, molecular mobility, conduction bands, etc. are
what you want to think about to understand causes. If you have a
world-class lab at your disposal, as I used to, you can infer a
fair bit about them by using lots of frequencies. But, living in
retirement, I'm limited to three: 2.45 GHz (microwave), audio (I
advise my son on old tube guitar amps occasionally) and DC. So,
I'll lash up a high voltage power supply to measure the DC
electrical properties of my conducting samples. (My ohm meter,
like most, only uses 1.5V, too low to bypass band gaps; none of
my samples show anything with it.)
John Sankey
---------
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John Sankey on sat 12 apr 08
"is it only iron that causes overheating in a microwave appliance?"
As I noted early on, there are two mechanisms by which a microwave can heat
things, molecular
(sometimes called dielectric absorption) and resistive.
Anything that is conductive will heat up in a microwave, aluminum foil being
the most common
culprit in kitchens. Lead or any other metal in a glaze could. And, there
are many compounds that
are conductive when components aren't - semiconductors are based on that. So
far, only
magnesium-phosphorous and iron have for me, both under unusual circumstances
(huge
overdose in the case of iron). Lee Love reports copper and titanium can.
"I love the cup but will I GLOW over time?"
Definitely not! Microwaves have nowhere near the energy to create
radioactivity.
"the object in question need not be incredibly electrically conducive."
Correct.
"[microwaves are] much more efficient at heating substances where the
molecules are free to
move, like water, than substances that are solid, like a glaze."
True for direct molecular heating - just compare liquid water to ice in a
microwave. But, not true
for resistive heating.
"why it is that many of us on-list are more accustomed to thinking of
elements and compounds as
stand-alone additions to our glazes and clay bodies than as participants in
chemical reactions that
form new materials?"
Check a mineral site such as http://webmineral.com/ - there are so many
possible minerals that
can be made from the components of our glazes that it makes the head spin!
But, if you want to
understand glaze chemistry, there's no other option. I don't blame potters
one bit for focussing on
other more important things such as form, function, feel...
John Sankey
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