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saltwater resistance

updated wed 20 oct 10

 

Eric Lindgren on thu 14 oct 10


Dear Mass Mind,
A potter friend of mine needs some information regarding wheteher
stoneware clay and glazes are resistant to saltwater; ie. ocean or
swimming pool salt levels.

She said: I have been asked to make a sculpture for a salt water
tank. I am a bit concerned about the salt leaching chemicals from
glaze so I thought I would just do it with raw clay and rub iron
oxide into it.

The man who installed the tank says the piece should be completely
glazed. I think raw clay and RIO would be just like having a hunk of
rock in the tank.

What do you think? I'll relay to her as she isn't a Clayart member.

Thanks,
Eric Lindgren
http://www.lindgrenpottery.com

Robert Harris on fri 15 oct 10


Well vitrified stoneware should be as inert as rock, as you say. Very
soft glazes - those without much alumina, or with poor silica alumina
ratios etc - may well be prone to some weathering and leaching. I
would certainly be tempted to err on the side of more matt and
"natural-looking" glazes that would not show the effects of surface
erosion as easily - especially if the water is moving significantly
over the sculpture (i.e. in a fountain) where physical (rather than
chemical) erosion might be a problem.

Incidentally chlorinated swimming pools are going be a lot more
"reactive" than a saltwater tank. Again, clay itself, and well
formulated glazes are unlikely to be affected, but anything soft is
going to be a problem. Using domestic-ware type glazes is probably a
good bet. A dishwasher is a significantly harsher environment than a
swimming pool or the ocean.

Robert



On Thu, Oct 14, 2010 at 1:38 PM, Eric Lindgren wrote=
=3D
:
> Dear Mass Mind,
> A potter friend of mine needs some information regarding wheteher
> stoneware clay and glazes are resistant to saltwater; ie. ocean or
> swimming pool salt levels.
>
> She said: I have been asked to make a sculpture for a salt water
> tank. =3DA0I am a bit concerned about the salt leaching chemicals from
> glaze so I thought I would just do it with raw clay and rub iron
> oxide into it.
>
> The man who installed the tank says the piece should be completely
> glazed. =3DA0I think raw clay and RIO would be just like having a hunk of
> rock in the tank.
>
> What do you think? I'll relay to her as she isn't a Clayart member.
>
> Thanks,
> Eric Lindgren
> http://www.lindgrenpottery.com
>



--=3D20
----------------------------------------------------------

Lee Love on fri 15 oct 10


On Thu, Oct 14, 2010 at 12:38 PM, Eric Lindgren wrot=
=3D
e:

> What do you think? I'll relay to her as she isn't a Clayart member.

The pH of a saltwater tank is between 7.6 and 8.4. It should be no
problem for a sound glaze. I would guess a good glaze would be a
better bet than iron. Iron rusts exposed to saltwater.

--=3D20
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/

=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi

David Finkelnburg on fri 15 oct 10


Eric,
YES! It is possible to make glazed clay work resistant to ocean or
swimming pool chemistry. That's why every pool I have ever seen uses glaze=
d
ceramic tile around the rim, at least.
You are correct, of course, that fired clay, if vitrified, will also b=
e
durable. However, bare clay is not easy to clean if it gets dirty but a
glazed surface usually is. Also, you do need to consider the possibility
that the iron oxide will leach into the water. You won't want to stain the
tank rust red. :-(
However, if one doesn't know the answer to your original question, it
is quite unlikely one would understand how to make durable glazed work in
the first place. So, in addition to conveying the answer, you really need
to advise your friend to investigate what is required to make glazes
durable.
The book "Mastering Cone 6 Glazes" by Hesselberth and Roy is a good
starting point. Clayart is a great resource. Simply using a favorite or
familiar and reliable glaze and assuming it will be chemically durable is
risky.
Good luck!
Dave Finkelnburg
http://www.mattanddavesclays.com

-----------------------------
On Thu, 14 Oct 2010 Eric Lindgren wrote:
A potter friend of mine needs some information regarding wheteher
stoneware clay and glazes are resistant to saltwater; ie. ocean or
swimming pool salt levels.
She said: I have been asked to make a sculpture for a salt water
tank. I am a bit concerned about the salt leaching chemicals from
glaze so I thought I would just do it with raw clay and rub iron
oxide into it.
The man who installed the tank says the piece should be completely
glazed. I think raw clay and RIO would be just like having a hunk of
rock in the tank.

Robert Harris on fri 15 oct 10


Lee - Iron Oxide is already "rust". By firing it should be
incorporated into the silica-alumina matrix. No problem.

R

On Fri, Oct 15, 2010 at 1:02 AM, Lee Love wrote:
> On Thu, Oct 14, 2010 at 12:38 PM, Eric Lindgren wr=
=3D
ote:
>
>> What do you think? I'll relay to her as she isn't a Clayart member.
>
> The pH of a saltwater tank is between 7.6 and 8.4. =3DA0 It should =3DA0b=
e no
> problem for a sound glaze. =3DA0 =3DA0I would guess a good glaze would be=
a
> better bet than iron. =3DA0 Iron rusts exposed to saltwater.
>
> --
> --
> =3DA0Lee, a Mashiko potter in Minneapolis
> http://mingeisota.blogspot.com/
>
> =3D93Observe the wonders as they occur around you. Don't claim them. Feel
> the artistry moving through and be silent.=3D94 --Rumi
>



--=3D20
----------------------------------------------------------

Stephani Stephenson on fri 15 oct 10


one thought is , you could refer to the American national Standards (ANSI=
=3D
)
for tile.
They test commercial pool tile, as well as other types, to see if it me=
=3D
ets
established standards. They publish the tests and requirements for such
tile, and just reading about the standards and the testing is helpful, ev=
=3D
en
if you never get your own work tested. it helps you understand what the
factors are.=3D20
Right now my own copies of the publications are still packed, otherwise i=
=3D

would look it up for you.

Even though you are referring to vessels, there might be some helpful inf=
=3D
o
from the tile industry.=3D20

it all depends on what your needs are for the particular situation.=3D20

for example, one of the beauties of underwater sculpture might be a
certain degree of interaction with the saline environment.

here's a link to some of standards info which may or may not prove usefu=
=3D
l.

http://www.tileusa.com/profile_main.htm

Stephani Stephenson

C Sullivan on fri 15 oct 10


I'm guessing that a Cone 10 glaze would be more durable than a Cone 6 glaze
in saltwater. Don't you think ???
Chae



On Fri, Oct 15, 2010 at 9:09 AM, David Finkelnburg
wrote:

> Eric,
> YES! It is possible to make glazed clay work resistant to ocean or
> swimming pool chemistry. That's why every pool I have ever seen uses
> glazed
> ceramic tile around the rim, at least.
> You are correct, of course, that fired clay, if vitrified, will also =
be
> durable. However, bare clay is not easy to clean if it gets dirty but a
> glazed surface usually is. Also, you do need to consider the possibility
> that the iron oxide will leach into the water. You won't want to stain t=
he
> tank rust red. :-(
> However, if one doesn't know the answer to your original question, it
> is quite unlikely one would understand how to make durable glazed work in
> the first place. So, in addition to conveying the answer, you really nee=
d
> to advise your friend to investigate what is required to make glazes
> durable.
> The book "Mastering Cone 6 Glazes" by Hesselberth and Roy is a good
> starting point. Clayart is a great resource. Simply using a favorite or
> familiar and reliable glaze and assuming it will be chemically durable is
> risky.
> Good luck!
> Dave Finkelnburg
> http://www.mattanddavesclays.com
>
> ------------------------------
> On Thu, 14 Oct 2010 Eric Lindgren wrote:
> A potter friend of mine needs some information regarding wheteher
> stoneware clay and glazes are resistant to saltwater; ie. ocean or
> swimming pool salt levels.
> She said: I have been asked to make a sculpture for a salt water
> tank. I am a bit concerned about the salt leaching chemicals from
> glaze so I thought I would just do it with raw clay and rub iron
> oxide into it.
> The man who installed the tank says the piece should be completely
> glazed. I think raw clay and RIO would be just like having a hunk of
> rock in the tank.
>

Lee Love on fri 15 oct 10


On Fri, Oct 15, 2010 at 11:21 AM, Robert Harris w=
=3D
rote:
> Lee - Iron Oxide is already "rust". By firing it should be
> incorporated into the silica-alumina matrix. No problem.


Rust can still leach. It makes no sense to coat with iron vitreous
stoneware or well glazed stoneware to make more resistant to the salt
water.
--
=3DA0Lee, a Mashiko potter in Minneapolis
http://mingeisota.blogspot.com/

=3D93Observe the wonders as they occur around you. Don't claim them. Feel
the artistry moving through and be silent.=3D94 --Rumi

John Baymore on sat 16 oct 10


Hi all in CLAYART land.... haven't posted in years now.


Eric,

Lee hit the Ph stuff dead on.

Another potential consideration is maintaining the good health of the fish =
=3D
and other marine life in the tank. I used to keep saltwater aquariums year=
=3D
s ago... and that is another possible side to the coin. Some salt water sp=
=3D
ecies are VERY hard to keep (particularly invertebrates) and many organisms=
=3D
can be VERY expensive. Water chemistry and purity can be rather problemat=
=3D
ic. Marine keeping makes fresh water tanks look really simple.

So the potential deterioration issue goes beyond the look of the ceramic pi=
=3D
ece. If the glaze or exposed clay body is leaching any chemistry into the =
=3D
water... it could potentially be dertrimental to the tank's residents. The=
=3D
larger the gallon capacity of the tank relative to the overall surface are=
=3D
a of the ceramic piece.... the less issue this might be. But it is worth a=
=3D
thought or two.

best,

.............john

John Baymore
River Bend Pottery
http://www.nhia.edu/new-facultypage-5/





Date: Fri, 15 Oct 2010 00:02:35 -0500
rom: Lee Love
ubject: Re: Saltwater resistance
On Thu, Oct 14, 2010 at 12:38 PM, Eric Lindgren wrot=
=3D
=3D3D
:
> What do you think? I'll relay to her as she isn't a Clayart member.
The pH of a saltwater tank is between 7.6 and 8.4. It should be no
roblem for a sound glaze. I would guess a good glaze would be a
etter bet than iron. Iron rusts exposed to saltwater.
--=3D3D20
-
A0Lee, a Mashiko potter in Minneapolis
ttp://mingeisota.blogspot.com/
=3D3D93Observe the wonders as they occur around you. Don't claim them. Feel
he artistry moving through and be silent.=3D3D94 --Rumi

C Sullivan on sat 16 oct 10


Good Mornin' David and John

Thanks for the feedback.
I believe you, both, are absolutely right !
Should have thought this thru more - before - putting 6 feet into mouth . .
. .
Hugs
Chae



On Sat, Oct 16, 2010 at 6:57 AM, John Hesselberth
wrote:

>
> On Oct 15, 2010, at 1:12 PM, C Sullivan wrote:
>
> > I'm guessing that a Cone 10 glaze would be more durable than a Cone 6
> glaze
> > in saltwater. Don't you think ???
>
> Hi Chae,
>
> I've seen no evidence of that. You can make durable glazes or non-durable
> glazes at either temperature. It all depends on whether the glaze is
> properly formulated for that temperature.
>
> Regards,
>
> John
>
>
> John Hesselberth
> http://www.masteringglazes.com
> http://www.frogpondpottery.com
>
> "I love everything that's old: old friends, old times, old manners, old
> books, old wines." Oliver Goldsmith, "She Stoops to Conquer" (1773)
>
>
>
>

John Hesselberth on sat 16 oct 10


On Oct 15, 2010, at 1:12 PM, C Sullivan wrote:

> I'm guessing that a Cone 10 glaze would be more durable than a Cone 6 =3D
glaze
> in saltwater. Don't you think ???

Hi Chae,

I've seen no evidence of that. You can make durable glazes or =3D
non-durable glazes at either temperature. It all depends on whether the =3D
glaze is properly formulated for that temperature.

Regards,

John


John Hesselberth
http://www.masteringglazes.com
http://www.frogpondpottery.com

"I love everything that's old: old friends, old times, old manners, old =3D
books, old wines." Oliver Goldsmith, "She Stoops to Conquer" (1773)

David Finkelnburg on sat 16 oct 10


Dear Chae,
You voice a common misconception. Firing temperature does not, per se,
cause durability. Rather, as Rober Harris notes, the ratio of alumina to
silica and the amount of both, relative to the amount of flux and the kind
of flux, is what determines durability. For the materials to melt at C10 v=
s
C6, of course, the ratios of flux to Al2O3 & SiO2 need to be different.
Properly formulated glazes at either temperature should be equally
chemically durable.
Good glazing!
Dave Finkelnburg
http://www.mattanddavesclays.com

-----------------------------
On Fri, 15 Oct 2010 C Sullivan wrote:
I'm guessing that a Cone 10 glaze would be more durable than a Cone 6 glaze
in saltwater. Don't you think ???

Ron Roy on sat 16 oct 10


Hi Chae,

A durable cone 6 glaze will be better than an unstable cone 10 glaze.

The way to tell if a glaze is likely to be durable is to "see" the
amount of SiO2 and Al2O3 in the glaze buy calculation or by having
glazes tested in a lab for leaching.

In other words - the cone fired is no way to determine durability.

RR



Quoting C Sullivan :

> I'm guessing that a Cone 10 glaze would be more durable than a Cone 6 gla=
ze
> in saltwater. Don't you think ???
> Chae
>
>
>
> On Fri, Oct 15, 2010 at 9:09 AM, David Finkelnburg
> wrote:
>
>> Eric,
>> YES! It is possible to make glazed clay work resistant to ocean or
>> swimming pool chemistry. That's why every pool I have ever seen uses
>> glazed
>> ceramic tile around the rim, at least.
>> You are correct, of course, that fired clay, if vitrified, will also=
be
>> durable. However, bare clay is not easy to clean if it gets dirty but a
>> glazed surface usually is. Also, you do need to consider the possibilit=
y
>> that the iron oxide will leach into the water. You won't want to stain =
the
>> tank rust red. :-(
>> However, if one doesn't know the answer to your original question, i=
t
>> is quite unlikely one would understand how to make durable glazed work i=
n
>> the first place. So, in addition to conveying the answer, you really ne=
ed
>> to advise your friend to investigate what is required to make glazes
>> durable.
>> The book "Mastering Cone 6 Glazes" by Hesselberth and Roy is a good
>> starting point. Clayart is a great resource. Simply using a favorite o=
r
>> familiar and reliable glaze and assuming it will be chemically durable i=
s
>> risky.
>> Good luck!
>> Dave Finkelnburg
>> http://www.mattanddavesclays.com
>>
>> ------------------------------
>> On Thu, 14 Oct 2010 Eric Lindgren wrote:
>> A potter friend of mine needs some information regarding wheteher
>> stoneware clay and glazes are resistant to saltwater; ie. ocean or
>> swimming pool salt levels.
>> She said: I have been asked to make a sculpture for a salt water
>> tank. I am a bit concerned about the salt leaching chemicals from
>> glaze so I thought I would just do it with raw clay and rub iron
>> oxide into it.
>> The man who installed the tank says the piece should be completely
>> glazed. I think raw clay and RIO would be just like having a hunk of
>> rock in the tank.
>>
>

Terry O'Neill on sun 17 oct 10


Marion,=3D20

Please respond to the Peter Sohngen article on dilatometer testing of the=
=3D
=3D20
nature of cristobolite. You have obviously been avoiding it.

In layman's terms as opposed to dissertion (muddying the water).



And now I've got some remodeling to complete.

Neon-Cat on sun 17 oct 10


Ron, I=3D92m so glad you mentioned testing =3D96 those who need to reassure
clients should test under conditions normal for their own studio or
pottery. There are some real limitations to trying to predict glaze
durability using mathematical relationships based on silica-alumina
ratios or silica-alumina-flux ratios. The phrase =3D93properly formulated
glazes=3D94 sounds so catchy, but to my sense is kind of useless as used
by some of you guys here. There are lots of great studies on how
glazes weather that have been done, especially since the beginning of
this century in industry for fast and slow-fired floor tiles, sanitary
ware, dinnerware, etc. It is almost a fantasy head-trip to use the
limits you all do without much consideration given to the real
ingredients used in a glaze recipe or without understanding what
products are created in a fired glaze. This kind of an approach is
flawed and leads to wrong assumptions regarding what is and is not a
=3D91good=3D92 glaze or what might be suitable for a saltwater fish tank. W=
hy
you stick with problems related to acidity and never mention the
effects of alkaline cleaning solutions or foods & beverages (and now
saltwater) or even plain water has always puzzled me. The lemon test
misses so much. If you don=3D92t know how to properly formulate a glaze so
that it is resistant in alkaline solutions how can you say one should
look to silica-alumina ratios as the solution to this person=3D92s
problem? Or that reading Mastering Cone 6 Glazes will bring the needed
insight? Some glazes will be durable in acidic but not alkaline
environments, some in alkaline but not acidic environments, some will
fail (or survive) in acidic and alkaline environments, and some will
fail in plain water.

Not too long ago I recall that a representative for Laguna offered
tech support to the list. If I were making a glaze for a piece to
place in a saltwater tank (years ago I use to raise saltwater fish)
and was feeling lazy about figuring it out for myself I=3D92d call and ask
Laguna or some other reputable commercial glaze company for a glaze
recommendation based on the specific application and my firing
capabilities (like John Baymore wrote, some saltwater fish and even
plants can be quite sensitive to environment changes). If I were
making this glazed piece I=3D92d shoot for a glaze that produced a
homogeneous glassy phase or only such crystals like diopside,
plagioclase, quartz, or corundum and skip glazes with the phases I
know are unstable in alkaline environments. But that=3D92s a lot of
thinking and I have other things to do. Simple-composition, high-fire
(cone 8-10), high-gloss, clear or translucent glazes (they consist
almost entirely of a homogeneous glassy phase) or glossy glazes with
minimal and safe colorant oxides on a porcelain or porcelaneous
stoneware would be best. Skip sculptures with rough areas, abrupt
change of direction that might later crack, and fancy nooks & crannies
that could trap particles like food, fecal, and algae matter (these
provide focal points for glaze corrosion). If I had to, I=3D92d try a
glaze recipe with only a combination of these ingredients (not all
need be used): 38 =3D96 66 % (by weight) SiO2, 18 - 30 % CaO, 6 -13 % MgO,
20 % or so Al2O3, 0-3 % K2O, and/or 0-3 % Na2O, with minimal
miscellaneous goodies and then have it tested for alkaline (preferably
saltwater) durability.

You can try home testing for alkalinity by soaking a glazed piece in a
4% solution of alkaline cleaner made with detergent and including a
non-ionic surfactant (pH about 9 or so =3D96 check labels for ingredients)
for two days, then change to a fresh solution and continue soaking for
two more days. Big color or surface textural changes might be visible
to the naked eye, but this is usually the prelude for instrumental
analysis that detects weathering of glazes in alkaline environments.

A few important generalities: chemical durability is usually discussed
in terms of hydrolytic, alkali, and acid durability. Surface
composition and microstructure of the glaze are altered by many
different aqueous environments -- in alkaline environments the network
structure of glazes is destroyed by hydroxyl attack; in acidic
environments glazes weather by ion exchange of alkali ions by hydrogen
ions. Crystalline substances and the interfacial areas around, for
example, feldspar remnants are prone to attack by acids and bases.
Initial surface attack by acidic substances is not always bad =3D96 in
some cases a barrier to further attack forms and the rate of
destruction is slowed.

The chemical durability of glazes depends on
1) the chemical composition of un-fired glaze (frits may promote
different phases in glazes)
2) the chemical composition of the fired glaze;
3) the phase composition(s), if any, within the fired glaze;
4) the amount of crystalline and microcrystalline particles produced (if an=
=3D
y);
5) surface topography - rough or matt glazes weather more than smooth,
glossy glazes;
damaged glazes (pinholes, pitting, crazing, blistering, etc.) corrode
faster than unblemished glazes;
6) firing schedule (fast, slow heating and/or cooling =3D96 btw
crystalline phases can and do form during fast firing schedules),
atmosphere (oxidation, neutral, reduction), and whether or not a
successful firing occurred (under-fired, over-fired, stalled, aborted
and re-started kilns, etc. may promote corrosion later);
7) post-firing treatment =3D96 harsh cleaners or other solutions may open
closed porosity in a glaze;
8) mixing methods (sieving, ball milling, grinding, etc. vs. =3D93rougher=
=3D94
or sloppy mixing);
9) adding surface crystalline components to a glaze (as for tiles as a
means of providing slip resistance);
10) deviation from standard single glaze application (layering glazes
or dusting ashes on a glaze may change the durability of the base
glaze)

As with a clay body, ceramic scientists use X-ray diffraction (XRD)
along with scanning electron microscopy (SEM) to determine chemical
and phase composition. Additionally, EDX microanalysis and Wavelength
dispersive X-ray spectroscopy (WDS) are available to give the chemical
composition and the different phases of the glaze, surface topography
can be measured by optical microscope, and gloss by a reflectometer.

Good luck to your friend, Eric, in finding the perfect glaze for the
saltwater aquarium!

Yes, Clayart can be a wonderful place:>)

Marian Gooding
Neon-Cat Ceramics

Ron Roy on sun 17 oct 10


Hi Marian,

All this is covered well in our book in language everyone can =3D20
understand - pity you have not read it - it would save you a lot of =3D20
time and effort.

RR

Quoting Neon-Cat :

> Ron, I=3DE2=3D80=3D99m so glad you mentioned testing =3DE2=3D80=3D93 thos=
e who need to=3D
reassure
> clients should test under conditions normal for their own studio or
> pottery. There are some real limitations to trying to predict glaze
> durability using mathematical relationships based on silica-alumina
> ratios or silica-alumina-flux ratios. The phrase =3DE2=3D80=3D9Cproperly =
formula=3D
ted
> glazes=3DE2=3D80=3D9D sounds so catchy, but to my sense is kind of useles=
s as us=3D
ed
> by some of you guys here. There are lots of great studies on how
> glazes weather that have been done, especially since the beginning of
> this century in industry for fast and slow-fired floor tiles, sanitary
> ware, dinnerware, etc. It is almost a fantasy head-trip to use the
> limits you all do without much consideration given to the real
> ingredients used in a glaze recipe or without understanding what
> products are created in a fired glaze. This kind of an approach is
> flawed and leads to wrong assumptions regarding what is and is not a
> =3DE2=3D80=3D98good=3DE2=3D80=3D99 glaze or what might be suitable for a =
saltwater fis=3D
h tank. Why
> you stick with problems related to acidity and never mention the
> effects of alkaline cleaning solutions or foods & beverages (and now
> saltwater) or even plain water has always puzzled me. The lemon test
> misses so much. If you don=3DE2=3D80=3D99t know how to properly formulate=
a glaz=3D
e so
> that it is resistant in alkaline solutions how can you say one should
> look to silica-alumina ratios as the solution to this person=3DE2=3D80=3D=
99s
> problem? Or that reading Mastering Cone 6 Glazes will bring the needed
> insight? Some glazes will be durable in acidic but not alkaline
> environments, some in alkaline but not acidic environments, some will
> fail (or survive) in acidic and alkaline environments, and some will
> fail in plain water.
>
> Not too long ago I recall that a representative for Laguna offered
> tech support to the list. If I were making a glaze for a piece to
> place in a saltwater tank (years ago I use to raise saltwater fish)
> and was feeling lazy about figuring it out for myself I=3DE2=3D80=3D99d c=
all and=3D
ask
> Laguna or some other reputable commercial glaze company for a glaze
> recommendation based on the specific application and my firing
> capabilities (like John Baymore wrote, some saltwater fish and even
> plants can be quite sensitive to environment changes). If I were
> making this glazed piece I=3DE2=3D80=3D99d shoot for a glaze that produce=
d a
> homogeneous glassy phase or only such crystals like diopside,
> plagioclase, quartz, or corundum and skip glazes with the phases I
> know are unstable in alkaline environments. But that=3DE2=3D80=3D99s a lo=
t of
> thinking and I have other things to do. Simple-composition, high-fire
> (cone 8-10), high-gloss, clear or translucent glazes (they consist
> almost entirely of a homogeneous glassy phase) or glossy glazes with
> minimal and safe colorant oxides on a porcelain or porcelaneous
> stoneware would be best. Skip sculptures with rough areas, abrupt
> change of direction that might later crack, and fancy nooks & crannies
> that could trap particles like food, fecal, and algae matter (these
> provide focal points for glaze corrosion). If I had to, I=3DE2=3D80=3D99d=
try a
> glaze recipe with only a combination of these ingredients (not all
> need be used): 38 =3DE2=3D80=3D93 66 % (by weight) SiO2, 18 - 30 % CaO, 6=
-13 % =3D
MgO,
> 20 % or so Al2O3, 0-3 % K2O, and/or 0-3 % Na2O, with minimal
> miscellaneous goodies and then have it tested for alkaline (preferably
> saltwater) durability.
>
> You can try home testing for alkalinity by soaking a glazed piece in a
> 4% solution of alkaline cleaner made with detergent and including a
> non-ionic surfactant (pH about 9 or so =3DE2=3D80=3D93 check labels for i=
ngredie=3D
nts)
> for two days, then change to a fresh solution and continue soaking for
> two more days. Big color or surface textural changes might be visible
> to the naked eye, but this is usually the prelude for instrumental
> analysis that detects weathering of glazes in alkaline environments.
>
> A few important generalities: chemical durability is usually discussed
> in terms of hydrolytic, alkali, and acid durability. Surface
> composition and microstructure of the glaze are altered by many
> different aqueous environments -- in alkaline environments the network
> structure of glazes is destroyed by hydroxyl attack; in acidic
> environments glazes weather by ion exchange of alkali ions by hydrogen
> ions. Crystalline substances and the interfacial areas around, for
> example, feldspar remnants are prone to attack by acids and bases.
> Initial surface attack by acidic substances is not always bad =3DE2=3D80=
=3D93 in
> some cases a barrier to further attack forms and the rate of
> destruction is slowed.
>
> The chemical durability of glazes depends on
> 1) the chemical composition of un-fired glaze (frits may promote
> different phases in glazes)
> 2) the chemical composition of the fired glaze;
> 3) the phase composition(s), if any, within the fired glaze;
> 4) the amount of crystalline and microcrystalline particles produced =3D2=
0
> (if any);
> 5) surface topography - rough or matt glazes weather more than smooth,
> glossy glazes;
> damaged glazes (pinholes, pitting, crazing, blistering, etc.) corrode
> faster than unblemished glazes;
> 6) firing schedule (fast, slow heating and/or cooling =3DE2=3D80=3D93 btw
> crystalline phases can and do form during fast firing schedules),
> atmosphere (oxidation, neutral, reduction), and whether or not a
> successful firing occurred (under-fired, over-fired, stalled, aborted
> and re-started kilns, etc. may promote corrosion later);
> 7) post-firing treatment =3DE2=3D80=3D93 harsh cleaners or other solution=
s may o=3D
pen
> closed porosity in a glaze;
> 8) mixing methods (sieving, ball milling, grinding, etc. vs. =3DE2=3D80=
=3D9Croug=3D
her=3DE2=3D80=3D9D
> or sloppy mixing);
> 9) adding surface crystalline components to a glaze (as for tiles as a
> means of providing slip resistance);
> 10) deviation from standard single glaze application (layering glazes
> or dusting ashes on a glaze may change the durability of the base
> glaze)
>
> As with a clay body, ceramic scientists use X-ray diffraction (XRD)
> along with scanning electron microscopy (SEM) to determine chemical
> and phase composition. Additionally, EDX microanalysis and Wavelength
> dispersive X-ray spectroscopy (WDS) are available to give the chemical
> composition and the different phases of the glaze, surface topography
> can be measured by optical microscope, and gloss by a reflectometer.
>
> Good luck to your friend, Eric, in finding the perfect glaze for the
> saltwater aquarium!
>
> Yes, Clayart can be a wonderful place:>)
>
> Marian Gooding
> Neon-Cat Ceramics
>

ivor and olive lewis on mon 18 oct 10


A useful introduction to the corrosion of ceramic materials would be L.A.
Lay, "Corrosion Resistance of Technical Ceramics", National Physical
Laboratory, Teddington, Middlesex. pub H.M.S.O. ISBN 0-11-480051-0.
Although information is given relating to aqueous solutions of many common
acidic and basic solutions there are not direct references to Sea Water.

Ivor Lewis,
REDHILL,
South Australia

Terry O'Neill on mon 18 oct 10


Woops, wordo. Change dissertion to dissertation (still intentional muddy=
=3D
=3D20
water).


And now I'm out of time again. Back to remodel.

Neon-Cat on mon 18 oct 10


Dear Terry, was I suppose to respond to the Peter Sohngen article?

A dilatometer is not the right or accepted tool for the job where a
definitive analysis of a fired clay body is needed.

Good luck with your remodeling!

Marian Gooding
Neon-Cat Ceramics


On Sun, Oct 17, 2010 at 10:35 PM, Terry O'Neill wrot=
=3D
e:
> Marion,
>
> Please respond to the Peter Sohngen article on dilatometer testing of the
> nature of cristobolite. =3DA0You have obviously been avoiding it.
>
> In layman's terms as opposed to dissertion (muddying the water).
>
> And now I've got some remodeling to complete.

Neon-Cat on mon 18 oct 10


You=3D92re a vendor, Ron. I finally get it. It was unreasonable of me to
think that your interests and mine and some of the other clayart
members could possibly be the same. Your business seems to be product
promotion and defense by any means. So, just like any pop-up, I know
just what to do.

Simple, by the way, doesn=3D92t necessarily mean right or complete.
And, I=3D92ve never met, talked to, or corresponded with a single potter
that couldn=3D92t, if he or she wanted to, understand things at an
in-depth level. Like the rest of life, the world of clay is constantly
unfolding to all who wish to explore and go further.

One nice thing about this thread =3D96 I am left with the good examples
set by Lee and John B. who both provided important information in a
timely fashion, potter-to-potter. And I am so glad that Eric posted
and Liz and Joyce, in other threads, recommended him and his website =3D96
what an inspiration he provides as a fine, self-sufficient potter. He
mentioned in his excellent video that the life of a potter can be
challenging but then went on to demonstrate and show the fruits and
rewards that come from working steadily and being creative.

Marian Gooding
Neon-Cat Ceramics


On Sun, Oct 17, 2010 at 6:04 PM, wrote:
> Hi Marian,
>
> All this is covered well in our book in language everyone can understand =
=3D
-
> pity you have not read it - it would save you a lot of time and effort.
>
> RR

Vince Pitelka on tue 19 oct 10


Marian Neon-Cat wrote:
"You're a vendor, Ron. I finally get it. It was unreasonable of me to think
that your interests and mine and some of the other Clayart members could
possibly be the same. Your business seems to be product promotion and
defense by any means. So, just like any pop-up, I know just what to do."

Marian -
I thought that the Clayart membership had pretty much gotten over this kind
of snarky behavior, at least for a while. Your message above is
out-of-line, misplaced, and unproductive. I believe Ron has been on this
list at least as long as I have - about 16 years, and his record is that of
a generous and knowledgeable contributor. That was true for a very long
time before he and John "wrote the book." If you have reasons to disagree
with him and want us to see your point, then explain it in terms we can all
understand.

If you have been paying attention to Clayart at all in the time you been a
participant, then you know that most of us have the greatest respect for
Ron, and have profited greatly from his generosity. In my opinion, you owe
him an apology.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka@dtccom.net; wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka