Lynn Goodman Porcelain Pottery on tue 22 aug 06
You hit the nail right on the head. It is caused by the bottom glaze
being so much drier than the top glaze. These are the 2 things I do:
1) Don't wait so long between coats. I wait just until the bottom coat
is dry.
2) Add CMC to your glazes. (Yes, I know that's my answer to
everything--that's because it works.) The CMC forms a tough coat that
is resistant to water. 1 to 2% added dry to your dry mix will do the
trick. Just keep the glaze a little thicker than usual--CMC slows down
drying, causing a thinner coat.
Lynn
On Aug 22, 2006, at 12:14 PM, Mark Tigges wrote:
> Hello all,
>
> I was wondering if any of you seasoned experts can give me some tips.
>
> I often have the problem that a second coat of glaze over some other
> one, doesn't integrate. It cracks all over instead of drying
> smoothly.
>
> I suspect that this problem is due to the bottom one being too dry.
> It happens often if I put the new glaze on the second day.
>
> I have the problem frequently with R&J licorice over R&J variegated
> blue. So, it might be an issue with those two glazes. I'm not sure
> ...
>
> Is there any trick I'm unaware of to keep this from happening? I've
> thought of misting the first coat before dipping the second. But I
> haven't tried that yet.
>
> Thanks,
>
> Mark.
Lynn Goodman
Fine Porcelain Pottery
548 Court St.
Brooklyn, NY 11231
718-858-6920
Cell 347-526-9805
www.lynngoodmanporcelain.com
Elizabeth Priddy on tue 22 aug 06
This is all I got, and it is crude compared to the
technical explanation:
If the two glazes have significantly different clay
content, you need to apply the one with more clay
first, or closer to the bique and then the other one
which would need to be applied OVER it to alleviate
the problem.
The problem is that the higher clay content is more
like a slip and the lower is more like a glass slurry
and the one with more clay *needs* the 'suck' factor
of the bisque to hold it on.
Else the clay-y one will just set on top of the
glass-y one and crack and fall off.
The other method would be to apply the one that is
cracking to leather hard clay and then bisque and then
apply the other regular.
But that is just a theory. And the only reason I am
weighing in on a glaze issue is that this one seems to
be about applying it, not making it.
Good luck!
E
Elizabeth Priddy
Beaufort, NC - USA
http://www.elizabethpriddy.com
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Mark Tigges on tue 22 aug 06
Hello all,
I was wondering if any of you seasoned experts can give me some tips.
I often have the problem that a second coat of glaze over some other
one, doesn't integrate. It cracks all over instead of drying
smoothly.
I suspect that this problem is due to the bottom one being too dry.
It happens often if I put the new glaze on the second day.
I have the problem frequently with R&J licorice over R&J variegated
blue. So, it might be an issue with those two glazes. I'm not sure
...
Is there any trick I'm unaware of to keep this from happening? I've
thought of misting the first coat before dipping the second. But I
haven't tried that yet.
Thanks,
Mark.
--
http://www.m2crafts.ca
m2crafts [at] gmail
liz gowen on wed 23 aug 06
Mark I use these two glazes blue over black a lot. I think what may be =
the
problem is the glaze slop is too thick. Try thinning it down a bit. I =
have
not had a problem with cracking as the glaze dries. As far as them
interacting I find they do better on the lower part of a taller piece =
for
some reason. The top part I have been toying with increasing the melt
slightly to get the beautiful melding over the whole piece.=20
I often glaze the blue and the black on separate days and I usually
ladle or use the irrigation syringe to apply the blue over the black so =
I am
not holding them in a bucket for a count of three, the latter would tend =
to
give a thicker coat and perhaps the cracking on drying.
Hope this helps
Liz Gowen
.
I often have the problem that a second coat of glaze over some other =
one,
doesn't integrate. It cracks all over instead of drying smoothly.
I suspect that this problem is due to the bottom one being too dry. It
happens often if I put the new glaze on the second day.
I have the problem frequently with R&J licorice over R&J variegated =
blue.
So, it might be an issue with those two glazes. I'm not sure ...
William & Susan Schran User on thu 24 aug 06
On 8/22/06 12:14 PM, "Mark Tigges" wrote:
> I suspect that this problem is due to the bottom one being too dry.
> It happens often if I put the new glaze on the second day.
This is what I have found to be true in almost every instance, but I don't
know the mechanics of the process.
Applying a second glaze, or even a second coat of the same glaze, over the
first coat that has dried to the extent that most of the water has been
absorbed into the clay or evaporated, will result in the second coat
flaking/cracking or causing the first coat to flake from the pot.
I always apply the second glaze soon after the first has dried to the touch.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Lee Love on thu 24 aug 06
Many of Hamada's and Shimaoka's glaze techniques include
glaze layering. Resist is often used. My ash glazes usually
don't like other glazes on top of them. What I learned during
my apprenticeship, was that when resist work is done with Mashiko
kaki, you have to switch from the standard ash glaze to a feldspathic
glaze, or else the top glaze will not hold.
Some glazes don't go well over others. Try different
combinations. Learn from what the materials are trying tell you.
--
Lee in Mashiko, Japan
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
Overall's on thu 24 aug 06
As soon as the "sheen" is gone that's when I apply
more glazes. This is only a matter of seconds so watch
carefully.
Kim in Houston
http://www.houstonpotters.com
--- William & Susan Schran User
wrote:
> On 8/22/06 12:14 PM, "Mark Tigges"
> wrote:
>
> > I suspect that this problem is due to the bottom
> one being too dry.
> > It happens often if I put the new glaze on the
> second day.
>
> This is what I have found to be true in almost every
> instance, but I don't
> know the mechanics of the process.
>
> Applying a second glaze, or even a second coat of
> the same glaze, over the
> first coat that has dried to the extent that most of
> the water has been
> absorbed into the clay or evaporated, will result in
> the second coat
> flaking/cracking or causing the first coat to flake
> from the pot.
>
> I always apply the second glaze soon after the first
> has dried to the touch.
>
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
>
>
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Kim Overall
http://www.houstonpotters.com
Ron Roy on tue 29 aug 06
Hi Mark,
The advice on applying the second coat before the first is dry is good.
The problem is - when dry the first coat has a powdery surface - so the
second coat cannot "bond" properly.
Ball clay can be substituted for kaolin to give a tougher surface to the
first coat - or adding some bentonite will also help if you have to let the
first coat dry completely - sill a better idea to add the second coat
before the first dries completely.
When subbing ball clay for kaolin it is best to do it using calculation
software so the alumina/silica ratio of a glaze can be kept the same.
RR
>I was wondering if any of you seasoned experts can give me some tips.
>
>I often have the problem that a second coat of glaze over some other
>one, doesn't integrate. It cracks all over instead of drying
>smoothly.
>
>I suspect that this problem is due to the bottom one being too dry.
>It happens often if I put the new glaze on the second day.
>
>I have the problem frequently with R&J licorice over R&J variegated
>blue. So, it might be an issue with those two glazes. I'm not sure
>...
>
>Is there any trick I'm unaware of to keep this from happening? I've
>thought of misting the first coat before dipping the second. But I
>haven't tried that yet.
>
>Thanks,
>
>Mark.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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