Tara and Michael on sat 29 mar 97
I just finished doing an absorption test on two clay samples to see if they
would be good for use in outdoor freeze-thaw situations. The result is
basically the ratio of the cold water absorption to the boiling water
absorption of the clay. The strange thing is that the boiled weight is
less than the cold water weight. This shouldn't happen unless I messed up
weighing. Is it me?!! The only other thing I can think of that would
explain this is that alot of water evaporated off the hot samples before I
could weigh them..
Any thought on this? How can best dry the samples completely so that I
can redo the test?
I copied the info on the test off of Tony Hansen's Digitalfire site. Here
is some of the info to help explain what I'm talking about:
>It is possible to perform a simple test based on the principle that a sample
>of fired ceramic boiled in water will absorb more moisture than one that is
>simply soaked. This is because for the former, the entire network is filled,
>for the latter only the pores. This test compares the cold soaking
>absorption or open porosity (C) of a clay with its boiled absorption or
>closed porosity (B). The structural ceramic industry requires a C/B result
>of less than 0.78 in order to pass CSA and ASTM specs for outdoor use.
>Variables
>
>Dry Weight - v1
> The weight of a dry test specimen of the fired clay.
>
>24hr Wet Weight - v2
> The weight of a specimen that has been soaked for 24 hours in room
> temperature water and wiped clean of all surface water.
>
>5hr Boiled Weight - v3
> The weight of a specimen that has been soaked for 24 hours and boiled
> for 5 hours and wiped clean of all surface water.
>
>Calculations
>
>24hr Absorption - C
> This is a calculation of the C value for this test, that is, the
> absorption of a clay sample if soaked for 24 hours in cold water.
>
> C = (v2 - v1) / v1
>
>5hr Boil Absorption - B
> This is a calculation of the B value, that is, the absorption of a clay
> bar if soaked for 24 hours and boiled for 5 hours.
>
> B = (v3 - v1) / v1
>
>Saturation Coefficient - S
> This is a calculation of the C/B value, the cold water absorption
> divided by the boiling water absorption.
>
> S = C / B
>
>The saturation coefficient S should be less than 0.78 in order to pass CSA
>and ASTM specs for outdoor use.
> URL of this page is http://digitalfire.com/magic/articles/outdoor.htm
Thanks, Michael Redwine
Tony Hansen on sun 30 mar 97
Tara and Michael wrote:
> I just finished doing an absorption test on two clay samples to see if they
> would be good for use in outdoor freeze-thaw situations...the boiled weight is
> less than the cold water weight. This shouldn't happen unless I messed up
> weighing. Is it me?!!
This does seem impossible. The test is done here every day at our brick
plant
and they use stoneware materials very similar to the pottery bodies
Plainsman
makes.
> How can best dry the samples completely so that I can redo the test?
Just throw them in a bisque kiln. I've had mixed results trying to dry
them
under a heat lamp or on top of a kiln. I assume you are blotting the
bars
thoroughly so there is no surface water when weighing. I make the bars 1
cm
(1/2 inch) thick.
--
=================================================================
Tony Hansen, IMC - Get INSIGHT 5 beta or The Magic of Fire II at
http://digitalfire.com or http://www.ceramicsoftware.com
LINDA BLOSSOM on sun 30 mar 97
Your clay is probably pretty tight. When I tried this the same thing
happened and I came to the conclusion that the water evaporated very
quickly. I tried several things-like adding cold water and then drying
quickly and getting it right on the scale. I did not take it out of the pan
and run to the studio - by then it had lost a lot of weight. When I added
cooler water, I just did this to the point where I could handle it. Then I
dried it well and put it on the digital scale. I watched the weight drop
at a pretty fast clip as the water evaporated out of the warm clay. I
dropped the flux back and opened up the body and had a better time of it,
getting the ratio I wanted.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
607-539-7912
blossom@lightlink.com
http://www.artscape.com
Ron Roy on sun 30 mar 97
>----------------------------Original message----------------------------
>I just finished doing an absorption test on two clay samples to see if they
>would be good for use in outdoor freeze-thaw situations. The result is
>basically the ratio of the cold water absorption to the boiling water
>absorption of the clay. The strange thing is that the boiled weight is
>less than the cold water weight. This shouldn't happen unless I messed up
>weighing. Is it me?!! The only other thing I can think of that would
>explain this is that a lot of water evaporated off the hot samples before I
>could weigh them..
I think you are right - run clod water over the tests before taking them
out of the pot - pat the excess water on the surface off with a paper towel
or such and weigh immediately.
>
>Any thought on this? How can best dry the samples completely so that I
>can redo the test?
Don't know how long it will take but keep them at 90C for as long as it
takes to get them back to the dry weight which you already know.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
ronroy@astral.magic.ca
koratpot@korat.loxinfo.co.th on mon 31 mar 97
Yeah, I got the same results when trying this test--the soaked
samples weighed more than the boiled samples. I attributed this two
two things: very fast evaporation of the water in the hot samples,
and the varying densities of hot and cold water. There is a definite
space within the sample for the water to occupy--it makes sense that
that volume filled with cold water would weigh more than the same
volume filled with hot.
I wish I could find a sample of clay where the boiled weight was more
than the soaked weight. I tried five different mixes, including one
with 40% grog, and one of concrete, and they were all the same. Made
me wonder if I understood the test.
Nikom
koratpot@korat.loxinfo.co.th
----------------------------Original message----------------------------
I just finished doing an absorption test on two clay samples to see if they
would be good for use in outdoor freeze-thaw situations. The result is
basically the ratio of the cold water absorption to the boiling water
absorption of the clay. The strange thing is that the boiled weight is
less than the cold water weight. This shouldn't happen unless I messed up
weighing. Is it me?!! The only other thing I can think of that would
explain this is that alot of water evaporated off the hot samples before I
could weigh them..
Tony Hansen on tue 1 apr 97
> I just finished doing an absorption test on two clay samples to see if they
> would be good for use in outdoor freeze-thaw situations. The result is
> basically the ratio of the cold water absorption to the boiling water
> absorption of the clay. The strange thing is that the boiled weight is
> less than the cold water weight. This shouldn't happen unless I messed up
> weighing. Is it me?!!
I phoned the boys at our brick division and they said two things that
might
have a bearing:
-They let the boiled samples cool down to room temperature, this could
take
5 hours or more, then they weigh.
-Very dense bodies do sometimes have a higher soaked weight, these
obviously
pass for outdoor use.
If your body is below 0.5% porosity you probably don't have to worry
about
doing this test anyway.
--
=================================================================
Tony Hansen, IMC thansen@mlc.awinc.com
INSIGHT5/Magic of Fire II demos at www.ceramicsoftware.com
LINDA BLOSSOM on wed 2 apr 97
It isn't entirely the temperature that is causing this. As I pointed out
earlier, when I dropped the flux in my clay, the results changed and the
boiled weight was greater and I achieved a ratio of .75 or so. Try firing
your clay to a lower temperature then try the test.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
607-539-7912
blossom@lightlink.com
http://www.artscape.com
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