Rimas VisGirda on fri 22 jan 10
Correct me if I'm wrong, from what I understand acidic liquids when applied=
to clay do 2 things. They allow the liquid to penetrate (break down) the c=
lay quicker than water thus penetrating into the clay more than H2O; they a=
lso don't expand the clay as much as wetting it with water. That may be the=
reason(s) that ceramic myths say to use vinegar instead of water when atta=
ching or patching...
Way back when I had a case of a bone dry pitcher that someone had tried to =
pick up by the body and broke out a piece of the wall, which piece later go=
t broken into 2. As an exercise I wanted to see if I could fix it and try t=
he properties of vinegar. This also has to do with my previous post about a=
moisture gradient.
So, I started by applying vinegar with a small brush to the broken edges, b=
eing careful not to smear the clay. As the vinegar softened the clay (broke=
n edge), I started to poke with a needle tool and applying more vinegar, al=
l the while being careful not to deform the broken edge. When the shine wen=
t away I poked some more and applied the vinegar until I had about 1/4 in. =
of darkened clay from the break into the wall, the clay at the break by thi=
s time was VERY wet but not quite slip. I applied a last coat of vinegar an=
d gently put the broken pieces into their original location on the pot -pro=
bably wiggled a little but it's been so long I forgot about the wiggle. Whe=
n the shine went away, I smoothed the break with a wooden tool, there was a=
darkened (wet) area of clay about a 1/2 in. wide radiating from the break.=
I can't remember if I covered the piece to dry or not, but probably not as=
i was sort of an impetuous youth. The piece drier without cracking.
The piece bisqued without cracking. I glazed and fired it (cone 10) and yo=
u would never know that there was a silver dollar sized wedge that had been=
replaced when it was bone dry...
Go figure... -Rimas
ivor & olive lewis on sat 23 jan 10
Dear Rimas VisGirda,
Most vinegar sold at the grocery store or supermarket is composed of 95
percent water and 5 percent Acetic Acid. It is probable, since these two
liquids have different vapour pressures and boiling points, that joints mad=
e
with vinegar remain moist.
I devised a way of using water to etch dry clay to expose the stress
structure and lamination of clay caused by kneading. Within a minute of
contacting water fragments of clay would detach themselves from the dry
solid mass.
Perhaps the acetic acid prevents destruction of the interwoven structures
of worked clay or in some way enhances the forces that bind the clay
fragments.
The relationship between Kaolin type clays and Water is unclear. I believe
there are difficulties in creating high magnification images that would
resolve the structure of clay water structures. Yes, individual clay
crystals have been photographed by Electron Microscopes. It has been
suggested that liquid water under the influence of Kaolin solidifies. But
that seems an illogical, if not a stupid and impossible suggestion
Best regards,
Ivor Lewis,
Redhill,
South Australia
James Freeman on sat 23 jan 10
On Sat, Jan 23, 2010 at 1:55 AM, ivor & olive lewis
wrote:
Most vinegar sold at the grocery store or supermarket is composed of 95
percent water and 5 percent Acetic Acid. It is probable, since these two
liquids have different vapour pressures and boiling points, that joints mad=
e
with vinegar remain moist.
Ivor, Rimas, et alii...
In this context, I believe one must consider the flocculatory effect of the
acetic acid in the vinegar. It is a common observation that breaks in
greenware repaired with water typically fail, while breaks repaired with
vinegar often survive. Vince pointed out (quite correctly) in another post
that a mechanical bond is necessary between joined clay parts. Such bonds
can occur on the microscopic scale between clay platelets (the Velcro
principle), or on a macro scale (which is the reason for, and justification
of, scoring). In dried greenware, or even leatherhard clay, the platelets
become more densely packed, and especially where the surface has been
worked, are probably approaching a tightly packed "card stack" structure.
Though vinegar is indeed mostly water, the acid constituent should operate
to flocculate the clay at the surface, giving it a "house of cards" (random=
)
structure (see Hamer; flocculation). This open "house of cards" structure
makes a mechanical interlock between the parts more probable, and therefore
makes the join more likely to survive until sintering, and ultimately the
glassy phase of full temperature firing, renders the piece monolithic.
Just my thoughts.
...James
James Freeman
"All I say is by way of discourse, and nothing by way of advice. I should
not speak so boldly if it were my due to be believed."
-Michel de Montaigne
http://www.jamesfreemanstudio.com
http://www.flickr.com/photos/jamesfreemanstudio/
http://www.jamesfreemanstudio.com/clayart/
ivor & olive lewis on sun 24 jan 10
Dewar James Freeman,
I thought the Velcro principle was that one surface had hooks and the
opposite side had loops. When opposite faces are brought together the hooks
engage in the loops. When they are separated, hooks straighten and slide
from the loops.
The House of Cards structure is hypothetical and as a hypothesis it has man=
y
flaws. One flaw is revealed when you do a volumetric calculation of the
spatial structure. This will show that cavities would be partially filled
with water when the clay water relationship is in the range that results in
a plastic mass. And if, as is claimed, water is a lubricant the particles
would slide past each other and the framework structure, as illustrated by
Frank Hamer, would collapse.
Without SEM images of wet clay we do not know !
Sincere regards,
Ivor Lewis,
Redhill,
South Australia
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