Dave Finkelnburg on thu 3 aug 06
Samantha,
I have used cone 5 and cone 10 ware outdoors here
in Idaho, both with and without glaze, and had no
problems with freeze/thaw damage.
I think you are mistaken about the glaze. It
isn't a liability, even if it's an imperfect coating
of the body. The secret is how you fire the clay.
In my case, I simply test a sample of the fired,
unglazed clay for absorption of water. For stoneware
I want less than 3% absorption. For porcelain I want
around 0.5% That indicates the clay is sufficiently
vitrified that it doesn't absorb enough water for
frost damage to occur. When clay that is fired to
that level of vitrification, glaze doesn't affect its
ability to withstand freezing weather.
You are right that colored clay costs more for
pigment than using a slip. If you color a slip made
from your clay body, and coat your work with that, you
should have a pretty good fit that is so chemically
similar to the body they will fire well together.
Good potting,
Dave Finkelnburg
--- Samantha Stankiewicz
wrote:
> I'm working on a series of outdoor pieces using a
> white cone 6 clay that fires to a lovely buttery
> color. I'm trying to figure out how to apply color
> so that the pieces are truly frost proof. As I
> understand so far, even with a claybody that has a
> low porosity, adding glaze is, in effect, like
> adding a layer which creates space for moisture to
> enter unless the glaze is so well matched that
> there are not even microscopic breaks in the glaze.
> This being fairly hard to produce on a regular
> basis, I'm thinking of using either underglaze and
> then seal with a wax coating or colored clay,
> slips or engobes. Does anyone have any experience
> with weather and color? If I do use colored
> clay, will it end up being extremely expensive(I'd
> like to start working larger). If I use an engobe,
> will it lay on the surface like a glaze?
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Samantha Stankiewicz on thu 3 aug 06
Hi,
I'm working on a series of outdoor pieces using a white cone 6 clay that fires to a lovely buttery
color. I'm trying to figure out how to apply color so that the pieces are truly frost proof. As I
understand so far, even with a claybody that has a low porosity, adding glaze is, in effect, like
adding a layer which creates space for moisture to enter unless the glaze is so well matched that
there are not even microscopic breaks in the glaze. This being fairly hard to produce on a regular
basis, I'm thinking of using either underglaze and then seal with a wax coating or colored clay,
slips or engobes. Does anyone have any experience with weather and color? If I do use colored
clay, will it end up being extremely expensive(I'd like to start working larger). If I use an engobe,
will it lay on the surface like a glaze?
Thanks,
Samantha
P.S. The goal is to have the ability to use color in the way a painter might.
Samantha Stankiewicz on fri 4 aug 06
Hi Dave,
Thanks for your response, but I'm a little confused. I was told by a number of people that the
glaze is the problem and that no glaze is completely stable from freeze/thaw because of
the way that moisture can make small pieces of the color pop off over time. Is this only in a low
fire environment? Maybe I'm just mixed up---quite possible for me!
Samantha
Dave Finkelnburg on fri 4 aug 06
Samantha,
You are welcome. I am the first to admit I do
not understand all I know about this! :-) I do not
believe you are confused...but you have been given
poor advice. Just because some people have had
failures doesn't mean that it's impossible to make
durable fired clay surfaces for harsh weather service.
The fact is, there are millions of tons of glazed
low fire terra cotta tile and building ornamentation
in the US that have been exposed to freezing weather
for most of a century and have not been damaged. It is
necessary to achieve a good bond between body and
glaze, and that is more difficult at low fire.
I have taken close-up photos of low fire glazed
tile on the exterior of the Celadon Company's sales
office in Alfred, New York. Some of the glazes are
heavily crazed, some badly pitted, but they look fine.
These tile were glazed before 1903!
Serious testing and work went into making those
durable glazed tiles. You may not find it easy, but
you can do this, too. :-)
All the best,
Dave Finkelnburg
--- Samantha Stankiewicz
wrote:
> Hi Dave,
> Thanks for your response, but I'm a little confused.
> I was told by a number of people that the
> glaze is the problem and that no glaze is completely
> stable from freeze/thaw because of
> the way that moisture can make small pieces of the
> color pop off over time. Is this only in a low
> fire environment? Maybe I'm just mixed up---quite
> possible for me!
> Samantha
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Snail Scott on fri 4 aug 06
At 07:33 AM 8/4/2006 -0400, Samantha S wrote:
>...I was told by a number of people that the
>glaze is the problem and that no glaze is completely stable from
freeze/thaw because of
>the way that moisture can make small pieces of the color pop off over
time. Is this only in a low
>fire environment?
Many glazes work well outdoors. It's more
critical for low-fire work, though. With a
vitrified stoneware, many glazes will work,
because the clay itself is not as vulnerable.
For earthenware, it's gotta be pretty dang
close to perfect, and I'm still not sure
I'd trust it. I wouldn't risk selling a piece
like that, myself.
There is a lot of outdoor earthenware that's
going strong after 100 years in freeze-thaw
environments, but it's seldom glazed. As you
note, it's because moisture will penetrate
from any direction, through tiny cracks and
crazing, and become trapped behind the glaze.
When that trapped moisture freezes, it will
expand and burst the glaze layer, spalling it
off.
'Stable' is an ambiguous term, but usually it
implies chemical stability, not necessarily
a glaze that is uncrazed or structurally
strong.
If you want the wide range of low-fire color,
consider using a stoneware fired to maturity
with low-fire glaze applied afterward. This is
tricky to make work, but it may be more durable
long-term, especially if you can get the glaze
fit right. Also, don't overlook the lower end
of the stoneware range: most 'low-fire' colors
can be achieved at ^4-6.
Ron Roy on fri 4 aug 06
Hi Samantha,
I think the problem you are referring to is glaze fit.
Outdoor sculpture is subject to extreme temperatures compared to inside
sculpture.
Crazed glazes are not a problem but - if the expansion of a glaze is too
low - the glaze becomes too big for the clay during cooling - this can
result in a glaze fault called shivering - where pieces of glaze can pop
off - and even crack the clay.
Let me know if you are interested in finding out how to make sure the
clay/glaze fit is OK - and tell me what cone you will fire to.
RR
>Hi Dave,
>Thanks for your response, but I'm a little confused. I was told by a
>number of people that the
>glaze is the problem and that no glaze is completely stable from
>freeze/thaw because of
>the way that moisture can make small pieces of the color pop off over
>time. Is this only in a low
>fire environment? Maybe I'm just mixed up---quite possible for me!
>Samantha
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Samantha Stankiewicz on sun 6 aug 06
Thank you for your responses, here are a few more details. I was working with a commercial, low
porosity earthenware made for outdoor work. I felt that the clay was very stiff and not plastic
enough for me and I had one piece of an outdoor commission shatter and had to rebuild it. When
I asked questions it turned out that I may have fired it wrong because I soaked for a long time and
then let it go up in temperature about 150 degrees an hour instead of about 50 degrees an hour
which it would have liked better so it may have had problems because of that. I decided that I
needed a solution that I could rely on because I've sold the last 3 major pieces and I need to
be able to say that it is stable outdoors. I agree with you Snail that I wouldn't rely on any
earthenware/glaze fit at this point.
SO...I finally decided to join the cone 6 crew and changed clay bodies to a buttery white from
ceramic supply---one of Jeff Zamek's clay bodies---(a royal pain in the neck to go from red clay
to white and test clay bodies and wash every tool and change surfaces!) I'm still working on the
porosity test because I had to order a scale that could measure more accurately than mine.
I should mention that I have a very small studio and I work as an art teacher in a public school
during the year so it does not pay for me to mix my own clay or glaze. I did do some glaze
chemistry in college but I need the time I have in the studio to be focused on making work. This
being said, there are plenty of brilliant people like those on this list who have spent years
perfecting their lovely glazes and sell them in stores! Yippee! So the real question is more on
what to choose which is why I'm not sure I can really adjust for the perfect glaze fit. If I had a
perfect situation, I would use terra sigillatta because I love the waxy surface it creates. I don't
think it's a good idea, however because it seems that it needs to be applied at very specific times
and mixed sooooo carefully. So...I tried just underglaze, but I don't like the dry surface for the
whole piece. I also sieved different mason stains into a cone 6 satin from Spectrum and it's nice,
but a bit flat. I think I need to do a line blend test with a bunch of the satin mixtures to see if there
is anything interesting. I ordered a jar of commercial engobe and thought I'd try mixing the
mason stain into that to see the surface. I even tried using butchers wax over the underglaze but
it stinks and barely shows up as a surface.
If any of you have more ideas on how to get an interesting mixture that I could control by using
colorants or a mixture of colorants and underglazes and overglazes, or even a different type of
non-glaze surface that would be outdoor friendly, I'd be thrilled.
This is a new body of work and I'm trying to figure out the color. If you'd like to see some older
work, My husband and i have a website: www.homepage.mac.com/icreatemymark ----my newer
pieces are not on this yet---I'll try to put some pics up today, but you can get a glimse of where
I'm going. The concept is a series of "hortisculptures" where I can work with plants as an element
of sculpture. I created a piece that had 9 openings and had it planted at a small herb store in
Sugar Loaf NY and it was like painting with the plants. That is why I want to be able to create
interesting painterly surfaces.
Ok---this was a bit on the ramblin side, but all help is welcome. Thanks!
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