Snail Scott on sun 10 apr 11
On Apr 10, 2011, at 1:45 PM, Stephani Stephenson wrote:
> ... in the heyday of
> Architectural ceramics , firings that were slow, even a couple of days to=
a
> over a week, made for a stronger body....
> thoughts? observations? evidence? theory?
I think that vitrification is vitrification, regardless
of the speed at which it is achieved. However,
clay has thickness, and a faster-but-hotter firing
is likely to give (I would think) a less even melt,
and that the discrepancy would be greater when
the thickness of the piece is greater. A lower-but-
slower firing will achieve the same nominal heat-
work as registered by cones (which don't have
a range of thicknesses), but I think it's reasonable
to assume that better heat penetration and melt
would result, compared with a quicker firing.
Also, I'd expect fewer stress-related firing flaws.
-Snail
Stephani Stephenson on sun 10 apr 11
I am thinking of architectural clay bodies.=3D20
i often come across references than note that, in the heyday og
Architectural ceramics , firings that were slow, even a couple of days to=
=3D
a
over a week, made for a stronger body.
architectural bodies tend to have a lot of coarse particles, and the isde=
=3D
a
is, that more complete and thorough fusing would only happen in slower
firing.Of course, slower firings were in order due to the size, mass and
thickness of architectural components (as with brick)
slower firing would have been necessary to ensure complete burnout of
organic material, outgassing and thorough even firing of large scale wor=
=3D
k,
but the question of strength intrigues me and i'd like explore it and h=
=3D
ear
some feedback on the question
(For now, this question sets aside the issue of whether this makes sense
with regard to fuel consumption, studio scale work, etc, i am interested =
=3D
in
the strength question)
thoughts? observations? evidence? theory?
Stephani Stephenson
David Beumee on mon 11 apr 11
Everything you mentioned, particle size, choice of materials, body
composition, wall thickness, rate of temperature rise, choice of firing
atmosphere, cooling cycle, all constitute a set of variables which impact
your work, in your studio, in your kiln, at the temperature you fire. As
Rimas says, ceramics is so process oriented. There are so many variables to
consider. Successful body composition depends on narrowing many variables
according to your requirements and your wishes, and then conducting researc=
h
and testing, in this case, modulus of rupture or MOR testing. Contact Pete
Pinnell at the Univ. of Nebraska, Lincoln. One of his classes conducted MOR
testing on a variety of fired clay bodies to compare relative strength, for
which he posted the results on Clayart some years back. The same formula
could be used to test the relative strength of architectural bodies at
various lengths of firing time.
David Beumee
On Sun, Apr 10, 2011 at 12:45 PM, Stephani Stephenson <
revivalsteph@yahoo.com> wrote:
> I am thinking of architectural clay bodies.
> i often come across references than note that, in the heyday og
> Architectural ceramics , firings that were slow, even a couple of days to=
a
> over a week, made for a stronger body.
>
> architectural bodies tend to have a lot of coarse particles, and the isde=
a
> is, that more complete and thorough fusing would only happen in slower
> firing.Of course, slower firings were in order due to the size, mass and
> thickness of architectural components (as with brick)
> slower firing would have been necessary to ensure complete burnout of
> organic material, outgassing and thorough even firing of large scale wor=
k,
> but the question of strength intrigues me and i'd like explore it and
> hear
> some feedback on the question
>
> (For now, this question sets aside the issue of whether this makes sense
> with regard to fuel consumption, studio scale work, etc, i am interested =
in
> the strength question)
> thoughts? observations? evidence? theory?
>
> Stephani Stephenson
>
Ron Roy on mon 11 apr 11
Keeping in mind that all tested samples need to be the same size if
results are to be comparable.
RR
Quoting David Beumee :
> Everything you mentioned, particle size, choice of materials, body
> composition, wall thickness, rate of temperature rise, choice of firing
> atmosphere, cooling cycle, all constitute a set of variables which impact
> your work, in your studio, in your kiln, at the temperature you fire. As
> Rimas says, ceramics is so process oriented. There are so many variables =
to
> consider. Successful body composition depends on narrowing many variables
> according to your requirements and your wishes, and then conducting resea=
rch
> and testing, in this case, modulus of rupture or MOR testing. Contact Pet=
e
> Pinnell at the Univ. of Nebraska, Lincoln. One of his classes conducted M=
OR
> testing on a variety of fired clay bodies to compare relative strength, f=
or
> which he posted the results on Clayart some years back. The same formula
> could be used to test the relative strength of architectural bodies at
> various lengths of firing time.
>
> David Beumee
Ron Roy on mon 11 apr 11
Hi Stephani,
In high fired bodies a slow firing will encourage the growth of
mullite crystals - those needle like crystals provide strength
because they interlock.
I don't see that happening at lower firing temperatures but the
addition of mullite crystals to the clay mix will help in the same way.
Larger mesh size Kyanite is also needle like and will also provide
that same kind of mechanical strength.
Slower firings with highfire stoneware can also bring unacceptable
levels of cristobalite if clays are not formulated properly.
See Peter Sohngens article on the Studio Potter website to understand
this better. Where to download it.
http://studiopotter.org/pdfs/Sohng%20pps84-89.pdf
RR
Quoting Stephani Stephenson :
> I am thinking of architectural clay bodies.
> i often come across references than note that, in the heyday og
> Architectural ceramics , firings that were slow, even a couple of days to=
a
> over a week, made for a stronger body.
>
> architectural bodies tend to have a lot of coarse particles, and the isde=
a
> is, that more complete and thorough fusing would only happen in slower
> firing.Of course, slower firings were in order due to the size, mass and
> thickness of architectural components (as with brick)
> slower firing would have been necessary to ensure complete burnout of
> organic material, outgassing and thorough even firing of large scale wor=
k,
> but the question of strength intrigues me and i'd like explore it and h=
ear
> some feedback on the question
>
> (For now, this question sets aside the issue of whether this makes sense
> with regard to fuel consumption, studio scale work, etc, i am interested =
in
> the strength question)
> thoughts? observations? evidence? theory?
>
> Stephani Stephenson
>
Des & Jan Howard on tue 12 apr 11
Stephani
Here, architectural ceramics, ie roof & floor tiles,
chimney pots, letter boxes, path markers, finials,
etc., were fired together with bulk house bricks &
piping. The slow firing was to gradually dry the
bricks. The long firing was essential to produce, as
far as possible, evenness & desired vitrification
throughout the setting. The required vitrification was
the state that produced the strongest, most durable
ware from the body in use. Generally the same clay was
used for all ware, including bricks, milled finer for
thrown items.
Des
On Apr 10, 2011, at 1:45 PM, Stephani Stephenson wrote:
> ... in the heyday of
> Architectural ceramics , firings that were slow, even a couple of days to=
a
> over a week, made for a stronger body....
> thoughts? observations? evidence? theory?
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
-32.656072 149.840624
ivor and olive lewis on thu 14 apr 11
Dear Stephani,
I have been watching this thread with interest. In finding out about this
topic, rather than relying on common knowledge, I had a look in Kingery et
al, "Introduction to Ceramics". ISBN 0-471-47860-1 and then remembered I ha=
d
W. E. Brownell, "Structural Clay Products" ISBN 0-387-81382-9..
In Ch 6 Brownell makes the following point in discussing composition and
firing characteristics.
" Plastic clays require fillers which are sometimes inert in the firing
process while others must be classified as reactive. To make a dense, stron=
g
body, fluxes are also required. The 3-layer clay and micaceous minerals are=
,
in themselves, fluxes, but kaolinic clays require additional minerals that
will produce some melting at the firing temperature; however, the amount of
liquid phase developed in structural clay products must remain small,
probably about 2% or less. Excessive fluxing allows for plastic flow and
serious distortion of the ware under load", ....no doubt meaning Pyroplasti=
c
deformation..
The remainder of Ch. 6 is most informative and would be useful for studio
potters.
Sincere regards,
Ivor Lewis,
REDHILL,
South Australia
David Beumee on fri 15 apr 11
Thank you Ivor. Brownell's explanation is very clear. I'll try to find his
book.
David Beumee
On Thu, Apr 14, 2011 at 1:48 AM, ivor and olive lewis u
> wrote:
> Dear Stephani,
> I have been watching this thread with interest. In finding out about this
> topic, rather than relying on common knowledge, I had a look in Kingery e=
t
> al, "Introduction to Ceramics". ISBN 0-471-47860-1 and then remembered I
> had
> W. E. Brownell, "Structural Clay Products" ISBN 0-387-81382-9..
> In Ch 6 Brownell makes the following point in discussing composition and
> firing characteristics.
> " Plastic clays require fillers which are sometimes inert in the firing
> process while others must be classified as reactive. To make a dense,
> strong
> body, fluxes are also required. The 3-layer clay and micaceous minerals
> are,
> in themselves, fluxes, but kaolinic clays require additional minerals tha=
t
> will produce some melting at the firing temperature; however, the amount =
of
> liquid phase developed in structural clay products must remain small,
> probably about 2% or less. Excessive fluxing allows for plastic flow and
> serious distortion of the ware under load", ....no doubt meaning
> Pyroplastic
> deformation..
> The remainder of Ch. 6 is most informative and would be useful for studio
> potters.
> Sincere regards,
> Ivor Lewis,
> REDHILL,
> South Australia
>
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