iandol on tue 28 oct 03
Dear Friends,
<glaze. my take is that a good fire place, with mixed wood ash is a great =
source.>> Quote from Mel J.
I will have a go at this one, maybe belatedly, for Mel.
First I would agree with your assumption. Better chance of getting a =
consistent reliable material if it is collected over a winter season and =
bulk blended for an annual supply.
I have been exploring ash recently as a combination of Ash and Slate =
(Which nicely combines recent threads).
First of all I have tried two ways, washed and unwashed ash in the same =
series of samples. Preliminary 6 by 6 blends were made with Soda Felspar =
and Silica #400 (Commercial Minerals), Slate Powder (Mintaro Quarry) and =
Wood Ash (Fruit wood prunings). Unwashed ash was screened to minus #100. =
Washed ash was scoured three times then screened to minus #100
Mass increments on each axis of the tile followed the pattern of 7.14% =
to 42.85% in equal increments and each sample contained all materials.
Both tiles exhibited the same pattern of melting, sample for sample. =
There was increasing fusion as both Slate and Ash weights increased and =
decreasing fusion as proportions Felspar decreased and Silica increased.
There were two major differences between the two tiles. Firstly, =
colouration of the well fused samples was a dense, weak, dark green in =
the samples containing raw ash while the washed ash samples which fused =
well were a much paler, lighter green tone. The second major difference =
was the degree of segregation into two phases. This was prominent in the =
tile which used unwashed ash but almost unnoticeable in the tile with =
washed ash. This segregation increased with increasing increments of =
slate but decreased with increasing increments of ash. With approx 35% =
slate, 42 % Unwashed Ash, 14%silica and 7% Felspar the effect was =
similar to a Chun style glaze.
I would like someone to test the pH values of water from subsequent =
washing's. How often must the ash be washed to get down to pH 7. My =
experience is that after three washing's the pH is still above 8.
Logan Oplinger on wed 29 oct 03
On Tue, 28 Oct 2003 14:10:29 +1030, iandol wrote:
>Dear Friends,
>.....I would like someone to test the pH values of water from subsequent
washing's. How often must the ash be washed to get down to pH 7. My
experience is that after three washing's the pH is still above 8.
>
Hello Ivor,
I'm going to hazard a guess here, that it may not be possible to obtain a
wash water with a pH of 7. You of course know this is the pH of neutral
water without any additives, or water that has been buffered.
The initial washings remove predominantly the very soluble 'alkali' oxides
K2O and Na2O which cause the water to have a very high pH >12.
Because of the slight solubility of some of the 'alkaline' oxides CaO & MgO
remaining in ash, and the way these oxides react with water to form
hydroxide ions and raise the pH (Please don't ask me to write out the the
equations to support this!!), as long as these alkaline oxides remain in
the ash, they will continue to dissolve in and react with water to raise
the pH (the reason why the ash remains caustic enough to cause lime
burns). These oxides are CaO primarily and MgO. These are also the
fluxing oxides which assist the ash in melting, and which are desireable to
be retained in the ash.
A crude way to demonstrate this would be to make some lime water by adding
a small amount (1-5 grams) of hydrated lime (slaked lime), Ca(OH)2, to a
glass of water, stir and let settle. Then measure the pH of the water. If
I recall correctly, it should be above pH 9.
If you let this glass of lime water set open to the air for some time,
several days, a couple of weeks, the pH will gradually drop to near pH 7 as
the lime absorbes carbon dioxide from the air to form calcium carbonate,
CaCO3. (Has anyone ever whitewashed a fence or a stone wall? Same process!)
Of course, if anyone can show that any of what I have said here is false, I
will stand corrected.
Logan Oplinger
Another Pacific Island
iandol on fri 31 oct 03
Dear Logan Oplinger,=20
No fault to find with your argument there. But testing would confirm the =
facts. It might also remind people who are experimenting with Ash Glazes =
that materials which are even sparingly soluble will wick into a porous =
bisque body and influence the way the surface of the clay will respond =
as a glaze matures.
Thanks for your contribution.
Best regards,
Ivor Lewis. Redhill, South Australia
Ann Brink on fri 31 oct 03
Ivor wrote to Logan: "materials which are even sparingly soluble will wick
into a porous bisque body and influence the way the surface of the clay will
respond as a glaze matures."
Hello all,
That's exactly the idea I am getting really interested in....I am getting
tired of the layer of glass on the outside of pots- the clay seems lost. I
want to just flux the surface of the clay on some of them. After all, clay
and glaze are of the same "stuff"...just in differing proportions.
Have tried soda ash a few times and got a nice toasty effect when I used a
claybody of 75% ^10stoneware and 25% earthenware clay and fired it to cone 7
ox. Another thing I sometimes do with the exterior of pots is: Just barely
stir the bucket of glaze so as to have a very thin mixture and just give
the pot a quick dunk or wash. I do this mostly with a high iron glaze. Can
look good on a textured piece. Some experiments with ash are next.
Good firings!
Ann Brink in Lompoc CA
| |
|
