Eleanora Eden on tue 23 jan 07
Hi Eva and all,
I have been doing the tests for outdoor clay bodies according
to the parameters that Digitalfire gives.
According to this, which I think I have posted in toto on clayart before,
it is a 5 hour boiling period and the resulting C/B ratio is supposed to be
less than .5.
Peter King gave me some tiles he made and I tested them, they come in
just under .5. He is working at ^6.
I am very interested in the thesis that Val Cushing considers a ratio of .78
to be sufficient.
The Digitalfire article ends with a conjecture that adding paperclay may
be the ticket to increasing porosity without decreasing the absorption. In
my tests I am taking a clay body that meets the absorption goals and then adding
my wood powder to increase the porosity. Seems to be working very well. I have
easily gotten down to the .6 range by adding my wood powder.
Eleanora
>
>Here is the calculation from Val's handbook - he says that it is the
>standard test used in the ceramics industry for structural clay products.
>Dave you may find that your clay falls right in the correct range. Also the
>glaze must have an effect - terracotta is usually unglazed, fully allowing
>the pores to function, unlike many stoneware planters that are glazed at
>least on one side if not both.
>
>D= dry weight of test sample
>C= wet weight of sample after soaking at room temp for 24 hours (wipe off
>surface water before weighing)
>B = boiled weight after 2 hours in boiling water (again wipe before
>weighing)
>
>1. C - D / D = "C" value
>2. B - D / D = "B" value
>3. "C" value / "B" value = C/B ratio. The C/B ratio must be less than .78 -
>represents room for expansion in the pore structure.
--
Bellows Falls Vermont
www.eleanoraeden.com
stephani stephenson on tue 23 jan 07
Eleanora
i am looking at the Insight artice and the
Saturation coefficient referrred
to is .78, not .5
which is the same as Cushing/Randal coefficient
the
URL i am looking at is
http://ceramic-materials.com/cermat/education/105.html
is there another article you are referring to?
Stephani Stephenson
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stephani stephenson on tue 23 jan 07
Marek wrote
......." Luckily I had some tiles fired at two
different states, fully vitrified and what I called
frost proof ( a Staffordshire TerraCotta fired up to
Cone 3 - 1170 C), which is very slightly porous but
well fired. The vitrified tiles were the only ones
that broke over a winter season - none of my frost
proof tiles did, whereas 15% (nearly) of the vitrified
tiles did - an unacceptable level. Go figure."
Marek, see, this makes sense to me!
same goes with refiring...the ones lost are usually
the tiles with a vitreous and not so open claybody..
especially on the bigger thicker pieces...i have some
pieces when made with a certain clay, i can once fire
to cone 3 but that is it...whereas the clays which i
also would describe as more porous but well fired are
bullet proof. obviously refiring is more rigorous than
day /night and seasonal fluctuations, but a good
architectural clay had a certain look and feel to me.
so it is great to hear your experience. and i'm
looking forward to continuing to gain understanding of
exactly what those qualities are.
Stephani
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Eleanora Eden on wed 24 jan 07
Another thing I forgot to mention is that I put a whole lot of work both
high fire and low fire out in back of the house when we moved from
California in 1984 and the stuff is all still out there. That is over 20 years
of freeze and thaw cycles. Almost none of it is damaged at all.
I rescued something a couple of years ago and brought it into the house.
A big low fire piece. No damage. No effort was made to make any of
this stuff freeze-resistant.
Don't know what conclusions to draw from this, just another bit of evidence.
Eleanora
--
Bellows Falls Vermont
www.eleanoraeden.com
Eleanora Eden on wed 24 jan 07
Hi Stephani,
Well, jeepers, you sure are right. I see in the first paragraph the following
reference to the 5% figure. Or maybe I got it from the Peter King workshop.
Don't think I made it up, but of course that is also a possibility. I am really glad
you pointed this out to me.
"The brick industry considers any clay having under 5% porosity resistant to
freeze/thaw failure (regardless of its closed and open porosity)."
Eleanora
>Eleanora
>i am looking at the Insight artice and the
>Saturation coefficient referrred
>to is .78, not .5
>which is the same as Cushing/Randal coefficient
>
>the
>URL i am looking at is
>http://ceramic-materials.com/cermat/education/105.html
>
>is there another article you are referring to?
>Stephani Stephenson
>
>
>
>
>____________________________________________________________________________________
>The fish are biting.
>Get more visitors on your site using Yahoo! Search Marketing.
>http://searchmarketing.yahoo.com/arp/sponsoredsearch_v2.php
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Bellows Falls Vermont
www.eleanoraeden.com
Jeoung-Ah Kim on wed 24 jan 07
Dear Dave,
Your reply was the most precise that I asked.
And Eleanora’s point about paper clay was an interesting. Since I have been working with paper clay and composite for a long time, I have discussed here with colleagues about this matter previously.
At least, for our climate, or from the technical point of view, a porous ceramic body is more reasonable for the freeze-climates than a dense ceramic body.
As usual as my research routine, I checked up briefly previous and current ceramic research issue relate with cold climate ceramics. I found some possible references which previously done and ongoing nano-ceramic research for extreme climate.
I will comeback to you and ClayArt when I have more explicit and structured explanation is available.
Thanks for you all reply.
Yours,
Kim
Dr. Kim Jeoung-Ah
Speldosegatan 4
SE-42146, Västra Frölunda
Sweden
Tel: +46-739-849906
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