Dave Finkelnburg on thu 29 jun 06
Jorge,
I'm going to make this pretty basic so, hopefully,
anyone can understand, so please don't think I am
assuming you know nothing about this. Nothing could
be further from the truth!
There are two ways to make a glaze of workable
consistency. You can thin it down by adding enough
water. That gives you lower density. Or, you can add
little water, keep the glaze dense, yet add a
deflocculant and make the glaze behave as if it is
thick. I think that's what you saw.
When glaze particles are so attracted to each
other that they stick together due to electrostatic
attraction, the glaze forms loose clumps of solids. We
call this a "flocculated" glaze.
However, just because a glaze has a high density
does not necessarily mean it will appear "thick."
Addition of a deflocculant causes the electrostatic
attraction to have less effect. The solid particles
in the deflocculated glaze can get quite a bit closer
to each other, as must happen in a dense glaze,
without sticking to each other. Thus you can have a
dense glaze that appears thin and easy to use.
Gerstley borate is famous for causing glazes to
flocculate. I have had BIG lumps in such a glaze at a
density of 1.3! :-( On the other hand, using a
deflocculant I've mixed glaze to a density of 1.65 and
it was easy to apply.
The conentration of dissolved, positive, ions in a
glaze with clay in it controls the degree of
deflocculation of the glaze. The more positive the
ions, the fewer of them it takes to flocculate the
glaze. Aluminum(3+) chloride is a very powerful
deflocculant. Salts of magnesium and calcium, both
2+, are most commonly used as deflocculants. Sodium
and other monovalent (1+) salts work as deflocculants,
but they are weak.
Deflocculants, as I'm sure you know, must be used
carefully. A little lowers viscosity, but add too
much and the viscosity starts to rise again.
I hope this helps answer your question. And I
hope you have something to cheer about in the game
against Germany!
Dave Finkelnburg
--- Jorge Nabel wrote:
> Many a times I read " first adjust density, then
> adjust viscosity".
> A couple of days ago we were preparing a glaze,and
> although the glaze seemed
> to be lacking of water,my friend said he already put
> a lot.
> He put a little quantity aside and began to
> deffloculate it, till it became
> usable.
> I measured both densities, the large batch and the
> one deffloculated.
> And both were so different....The large one was 1.45
> and the deffloc was
> 1.55
> Sooo,I read in Clayart that this happens, I checked
> itīs true.
> I want to know why . Can someone explain this?
> I expected the non deffloc to be heavier.Not the
> opposite
> Even if my readings were wrong,I want to know why
> density changes.
> By the way, this glaze was an alumina matt
> Jorge en Buenos Aires, where the whole country will
> stop to watch the soccer
> match
> with Germany
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Paul Herman on thu 29 jun 06
Hello Jorge,
I think it works like this. A flocculated slip (one with epsom salts =20
added) causes the clay particles to attract each other in such a way =20
that causes less density. The electrical charge causes one platelet's =20=
edge to be attracted to the center of another. Like this: T .
A deflocculant (soda ash) will cause the edges of the clay platelets =20
to be attracted to each other. Like this: II .
So the flocculated slip is puffed up, and less dense.
Good luck with the soccer, Go Argentina!
Best,
Paul Herman
Great Basin Pottery
Doyle, California US
http://greatbasinpottery.com
On Jun 29, 2006, at 6:40 PM, Jorge Nabel wrote:
> Sooo,I read in Clayart that this happens, I checked it=B4s true.
> I want to know why . Can someone explain this?
> I expected the non deffloc to be heavier.Not the opposite
> Even if my readings were wrong,I want to know why density changes.
> By the way, this glaze was an alumina matt
> Jorge en Buenos Aires, where the whole country will stop to watch =20
> the soccer
> match
> with Germany
>
Jorge Nabel on thu 29 jun 06
Hi everybody. It=B4s been some time since my last post.Nothing special to s=
ay.
Now, finally something to ask.
Many a times I read " first adjust density, then adjust viscosity".
A couple of days ago we were preparing a glaze,and although the glaze seeme=
d
to be lacking of water,my friend said he already put a lot.
He put a little quantity aside and began to deffloculate it, till it became
usable.
I measured both densities, the large batch and the one deffloculated.
And both were so different....The large one was 1.45 and the deffloc was
1.55
Sooo,I read in Clayart that this happens, I checked it=B4s true.
I want to know why . Can someone explain this?
I expected the non deffloc to be heavier.Not the opposite
Even if my readings were wrong,I want to know why density changes.
By the way, this glaze was an alumina matt
Jorge en Buenos Aires, where the whole country will stop to watch the socce=
r
match
with Germany
Dave Finkelnburg on fri 30 jun 06
Paul,
The picture you drew, is an EXCELLENT way to
visualize flocculation and deflocculation.
I do object to saying flocculating a slip makes it
less dense. That is wrong. I think you totally
understand the only way to change slip density is to
change the amount of solids relative to the amount of
water.
It is more correct to say flocculating a slip makes
it appear thicker, even though it may be low in
density. I think that is what you meant.
I think that's also why Jorge noted the advice,
"Adjust density first, then viscosity." If you make a
slip dense, then you can deflocculate it and it works.
If you make a slip low in density, then you can
flocculate that and it works, too.
Hope it's not too dry for you there on the dry
side of the Sierras.
Dave Finkelnburg
--- Paul Herman wrote:
A flocculated slip (one
> with epsom salts
> added) causes the clay particles to attract each
> other in such a way
> that causes less density. The electrical charge
> causes one platelet's
> edge to be attracted to the center of another. Like
> this: T .
> A deflocculant (soda ash) will cause the edges of
> the clay platelets
> to be attracted to each other. Like this: II .
> So the flocculated slip is puffed up, and less
> dense.
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Paul Herman on fri 30 jun 06
Hello Dave,
Thank you for helping to clarify my thoughts. I understand it better
now, density is not the right word.
It's not too hot lately, and we've had some thunderstorms, which of
course rarely produce rain that gets all the way to the ground. They
start lots of fires, one yesterday a couple of miles away. I got out
the fire hose and tested it.
Best,
Paul Herman
Great Basin Pottery
Doyle, California US
http://greatbasinpottery.com
On Jun 30, 2006, at 10:11 AM, Dave Finkelnburg wrote:
> It is more correct to say flocculating a slip makes
> it appear thicker, even though it may be low in
> density. I think that is what you meant.
> I think that's also why Jorge noted the advice,
> "Adjust density first, then viscosity." If you make a
> slip dense, then you can deflocculate it and it works.
> If you make a slip low in density, then you can
> flocculate that and it works, too.
> Hope it's not too dry for you there on the dry
> side of the Sierras.
> Dave Finkelnburg
Ivor and Olive Lewis on sat 1 jul 06
Not sure if the what I read in clayart #176 is making sense of not.=20
Perhaps the first thing to do is to distinguish between "Density" and =
"Viscosity".=20
Density is about mass per unit volume. This may be Kg per Cubic Metre, =
Grams per Cubic Centimetre or per litre, Pounds per Gallon or Ounces per =
Pint.
Viscosity is about how well things will flow. This is related to the =
time a measured volume will flow through an aperture of an agreed size.
People who are slip casting like to have a clay/water mixture that it =
will flow freely and quickly with a high percentage of solids in a small =
volume of water. They also like their moulds to rapidly draw water from =
their slip so that the layer of clay builds up in as short a time as =
possible and remains firm. Their casting slip needs to have a high =
density and a low viscosity.
An ordinary mixture of clay and clean pure water that has the density =
needed for slip casting will be almost solid, a sticky paste that has a =
very high viscosity. This is because water and clay have a strong =
affinity for each other. If compounds called electrolytes are added to =
the water, they neutralise the forces that attract water to clay. This =
reduces the viscosity and the slip will flow freely.
One of the marvels of Nature is that Clay is able to solidify Water. But =
there are times when we do not wish it to do that. When the need arises =
we ask technicians what to do. They will tell us to use a Deflocculating =
Agent. The best rule seems to be "Get the Density right then adjust the =
Viscosity."
It is interesting to contrast Casting Slip with a Throwing Clay. In the =
former the Mass Ratio of solids to fluid may be as high as 90%/10% yet =
it will flow like water. In the latter where the Mass Ratio is 65%/35% =
it is a solid. This is even more astounding when you convert these mass =
ratios to volumetric ratios because throwing clay may have twice the =
volume of water in relation to the volume of clay.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
David Beumee on sun 2 jul 06
Dave wrote:
" Or, you can add
> little water, keep the glaze dense, yet add a
> deflocculant and make the glaze behave as if it is
> thick. I think that's what you saw.
My experience is different. Even a small amount of added deflocculant, such sodium silicate or Darvan, added to a glaze made with a small amount of water will become not only thin, but "sheet" off the pot, a terrible and annoying characteristic of deflocculated glazes.
" Salts of magnesium and calcium, both
> 2+, are most commonly used as deflocculants."
I have successfully used Magnesium sulphate, Epsom Salts, and Calcium Chloride, as powerful flocculating agents for decades. Both work extremely well to flocculate both glazes and clay body slurry.
David Beumee
-------------- Original message ----------------------
From: Dave Finkelnburg
> Jorge,
> I'm going to make this pretty basic so, hopefully,
> anyone can understand, so please don't think I am
> assuming you know nothing about this. Nothing could
> be further from the truth!
> There are two ways to make a glaze of workable
> consistency. You can thin it down by adding enough
> water. That gives you lower density. Or, you can add
> little water, keep the glaze dense, yet add a
> deflocculant and make the glaze behave as if it is
> thick. I think that's what you saw.
> When glaze particles are so attracted to each
> other that they stick together due to electrostatic
> attraction, the glaze forms loose clumps of solids. We
> call this a "flocculated" glaze.
> However, just because a glaze has a high density
> does not necessarily mean it will appear "thick."
> Addition of a deflocculant causes the electrostatic
> attraction to have less effect. The solid particles
> in the deflocculated glaze can get quite a bit closer
> to each other, as must happen in a dense glaze,
> without sticking to each other. Thus you can have a
> dense glaze that appears thin and easy to use.
> Gerstley borate is famous for causing glazes to
> flocculate. I have had BIG lumps in such a glaze at a
> density of 1.3! :-( On the other hand, using a
> deflocculant I've mixed glaze to a density of 1.65 and
> it was easy to apply.
> The conentration of dissolved, positive, ions in a
> glaze with clay in it controls the degree of
> deflocculation of the glaze. The more positive the
> ions, the fewer of them it takes to flocculate the
> glaze. Aluminum(3+) chloride is a very powerful
> deflocculant. Salts of magnesium and calcium, both
> 2+, are most commonly used as deflocculants. Sodium
> and other monovalent (1+) salts work as deflocculants,
> but they are weak.
> Deflocculants, as I'm sure you know, must be used
> carefully. A little lowers viscosity, but add too
> much and the viscosity starts to rise again.
> I hope this helps answer your question. And I
> hope you have something to cheer about in the game
> against Germany!
> Dave Finkelnburg
>
> --- Jorge Nabel wrote:
> > Many a times I read " first adjust density, then
> > adjust viscosity".
> > A couple of days ago we were preparing a glaze,and
> > although the glaze seemed
> > to be lacking of water,my friend said he already put
> > a lot.
> > He put a little quantity aside and began to
> > deffloculate it, till it became
> > usable.
> > I measured both densities, the large batch and the
> > one deffloculated.
> > And both were so different....The large one was 1.45
> > and the deffloc was
> > 1.55
> > Sooo,I read in Clayart that this happens, I checked
> > itīs true.
> > I want to know why . Can someone explain this?
> > I expected the non deffloc to be heavier.Not the
> > opposite
> > Even if my readings were wrong,I want to know why
> > density changes.
> > By the way, this glaze was an alumina matt
> > Jorge en Buenos Aires, where the whole country will
> > stop to watch the soccer
> > match
> > with Germany
>
>
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Ivor and Olive Lewis on mon 3 jul 06
I think there may be difficulties in giving an answer to problems =
relating to a glaze slop by suggesting deflocculants or flocculants be =
used to alter viscosity.
There seem to be many assumptions in much of what has been written so =
far. Most glaze formulations are conglomerate materials with a wide =
range of particle sizes and configurations the bulk of which will =
respond, if at all, only feebly to the effects of deflocculating or =
flocculating agents. Of the materials that will respond to such things =
as Darvan, Dispex or singly charged metallic ions in solution, those =
most affected will be clay minerals. Unless these are present in bulk in =
a recipe their influence on viscosity will be minimal. From memory, one =
percent Bentonite is sufficient to suspend most glazes. Further changes =
will be assisted by adding or removing water.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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