Robert Harris on fri 10 aug 12
Bill and Robin,
I notice that Bill puts his cracking and flaking at the feet of high
shrinkage zinc oxide, whereas I was suggesting to you that you need to
increase shrinkage.
Both of these problems (too much or too little shrinkage) can lead to
flaking - you'll need to figure out which one. If there is insufficient
shrinkage, the drying glaze layer will seem to lift off the pot, but
without necessarily producing cracks in the glaze layer - in fact you can
often feel blisters forming on a drying pot.
If there is too much shrinkage on the other hand I think you get fissures
forming, and you can feel the glaze layer release from the pot surface, but
not being pushed up from the pot surface like you do if there is
insufficient shrinkage.
Bill does this sound right? I have much less experience with this sort of
cracking.
Robert
On Fri, Aug 10, 2012 at 10:30 PM, William & Susan Schran User <
wschran@cox.net> wrote:
> On 8/10/12 6:26 PM, "Robin Wolf" wrote:
>
> >I am working on Cone 6 oil spot glazes, and am having a terrible time wi=
th
> >the application process.
> >
> >Cone 5 B-Mix bisqued to 04, dipping in the base glaze 3x as suggested in
> >other Clayart posts. I have tried dipping in the cover glaze when the
> >base
> >is still damp, but after a short time (glaze still looks damp), it looks
> >like it is blistering up and then cracks or flakes. So I tried drying t=
he
> >base glaze completely, even going so far as to place them in a 250* oven
> >to
> >make sure they are completely dry. Dipped 1x, 2x, and 3x on separate
> >pieces, all have fractured glazes. How do I stop the glaze from
> >fracturing
> >as it dries? I have a sprayer, but do I try spraying when the glaze is
> >still wet, or dry? Will the application method matter, or am I missing
> >something in the formulas?
>
> Robin, Perhaps this might help find a solution.
> I work with crystalline glazes fired at cone 6.
> These glazes contain no or very little clay.
> They also contain a high percentage of zinc that
> shrinks a great deal while drying.
> The only way I can brush apply 4 to 5 layers of glaze,
> resulting in a very thick glaze application, is to add a gum binder.
> I use a CMC solution instead of water.
> Others working with these glazes use Veegum-T for spraying.
> If I don't use the gum, all my glazes crack and peel off.
>
> Bill
> --
> William "Bill" Schran
> wschran@cox.net
> wschran@nvcc.edu
> http://www.creativecreekartisans.com
>
--
----------------------------------------------------------
Robin Wolf on fri 10 aug 12
Robert,
Thank you for the offer to run it through Glazemaster! Would really
appreciate it.
The original formula called for G200, did not have any and it is 50 miles t=
o
town (OKC) to get some, so I looked through the archives and saw where
several had substituted CF for the G200. I don't have Glazemaster, so just
did a direct 1:1 replacement. Since I am a novice (at best) at glaze
calculating, any help would be great. I can (almost) follow a recipe, whic=
h
is about the extent of my experience so far!
Do I need to redo the base and the cover glaze both, or just the cover
glaze?
I have plenty of bentonite on hand, no CMC though. I have small quantities
of the cover glaze, maybe a quart so no problem replacing them. I did a
small batch of the base, test fired it on 3 pieces, and had very few if any
flaking problems. I made the larger batch, 3 gallons, and the first glazed
pieces started flaking. Uggghhhh!
I have gotten some really decent oilspots from this glaze combo, like the
way the colors and spots come out, just did not know how to fix the flaking=
.
Robin Wolf
Robin Wolf Pottery
Kingfisher, OK
www.robinwolfpottery.com
From: Robert Harris
Your recipes are fairly low in clay and therefore you need a higher
shrinkage rate of the raw glaze. (It blisters because it's not shrinking
enough). I might sub a ball clay (e.g. OM 4) for the EPK. Obviously you'd
have to use a glaze calculator to get the silica:alumina ratios right - it'=
s
not a direct 1:1 sub - especially not with something as finicky as oil
spots. The other option is to add some bentonite (maybe subbing out a bit o=
f
the EPK), with the same basic concept - increase the shrinkage as it dries.
Robin Wolf on fri 10 aug 12
I am working on Cone 6 oil spot glazes, and am having a terrible time with
the application process.
Cone 5 B-Mix bisqued to 04, dipping in the base glaze 3x as suggested in
other Clayart posts. I have tried dipping in the cover glaze when the base
is still damp, but after a short time (glaze still looks damp), it looks
like it is blistering up and then cracks or flakes. So I tried drying the
base glaze completely, even going so far as to place them in a 250* oven to
make sure they are completely dry. Dipped 1x, 2x, and 3x on separate
pieces, all have fractured glazes. How do I stop the glaze from fracturing
as it dries? I have a sprayer, but do I try spraying when the glaze is
still wet, or dry? Will the application method matter, or am I missing
something in the formulas?
The recipes are as follows:
Oil Spot Combo #1 (three coats), specific gravity 165
Custer Feldspar
47.83
EPK
10.87
Red Iron Oxide
9.78
Silica
23.91
Whiting
17.39
Cover Glaze 2 coats
Custer Feldspar
30
Frit 3134
30
Silica
25
Kaolin--EPK
5
Zircopax
10
Total:
100
Copper Carb 4% =3D Green
Cobalt Carb 4% =3D Blue
Robin Wolf
Robin Wolf Pottery
Kingfisher, OK
www.robinwolfpottery.com
William & Susan Schran User on fri 10 aug 12
On 8/10/12 6:26 PM, "Robin Wolf" wrote:
>I am working on Cone 6 oil spot glazes, and am having a terrible time with
>the application process.
>
>Cone 5 B-Mix bisqued to 04, dipping in the base glaze 3x as suggested in
>other Clayart posts. I have tried dipping in the cover glaze when the
>base
>is still damp, but after a short time (glaze still looks damp), it looks
>like it is blistering up and then cracks or flakes. So I tried drying the
>base glaze completely, even going so far as to place them in a 250* oven
>to
>make sure they are completely dry. Dipped 1x, 2x, and 3x on separate
>pieces, all have fractured glazes. How do I stop the glaze from
>fracturing
>as it dries? I have a sprayer, but do I try spraying when the glaze is
>still wet, or dry? Will the application method matter, or am I missing
>something in the formulas?
Robin, Perhaps this might help find a solution.
I work with crystalline glazes fired at cone 6.
These glazes contain no or very little clay.
They also contain a high percentage of zinc that
shrinks a great deal while drying.
The only way I can brush apply 4 to 5 layers of glaze,
resulting in a very thick glaze application, is to add a gum binder.
I use a CMC solution instead of water.
Others working with these glazes use Veegum-T for spraying.
If I don't use the gum, all my glazes crack and peel off.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Robert Harris on fri 10 aug 12
I do some overdipped oil spots (cone 10 though), and have had a few
problems on occasion.
Your recipes are fairly low in clay and therefore you need a higher
shrinkage rate of the raw glaze. (It blisters because it's not shrinking
enough). I might sub a ball clay (e.g. OM 4) for the EPK. Obviously you'd
have to use a glaze calculator to get the silica:alumina ratios right -
it's not a direct 1:1 sub - especially not with something as finicky as oil
spots. The other option is to add some bentonite (maybe subbing out a bit
of the EPK), with the same basic concept - increase the shrinkage as it
dries.
The other thing to do is add some CMC gum - I have less experience with
this, but certainly for minor stuff it works.
The third thing is that I do the second dip as soon as I have a dry(ish)
bottom layer. (i.e. it's no longer shiny, but is still cool to the touch).
I then dry as slowly as possible (within reason).
This last really only works if it's only just on the edge of not cracking
off.
Oh and one last thing - make sure you really need those glaze layers as
thick as you're making them. With one glaze oilspots, without a doubt you
need to get it on thick, but I have found that if I put on a thin (ish)
layer of my one glaze oilspot, and then cover it with another glaze, it
still spots really well.
Hope something there helps. I'm happy to do the subbing out with a ball
clay or bentonite if you need help with glaze calculation.
Robert
On Fri, Aug 10, 2012 at 6:26 PM, Robin Wolf wrote:
> I am working on Cone 6 oil spot glazes, and am having a terrible time wit=
h
> the application process.
>
> Cone 5 B-Mix bisqued to 04, dipping in the base glaze 3x as suggested in
> other Clayart posts. I have tried dipping in the cover glaze when the ba=
se
> is still damp, but after a short time (glaze still looks damp), it looks
> like it is blistering up and then cracks or flakes. So I tried drying th=
e
> base glaze completely, even going so far as to place them in a 250* oven =
to
> make sure they are completely dry. Dipped 1x, 2x, and 3x on separate
> pieces, all have fractured glazes. How do I stop the glaze from fracturi=
ng
> as it dries? I have a sprayer, but do I try spraying when the glaze is
> still wet, or dry? Will the application method matter, or am I missing
> something in the formulas?
>
> The recipes are as follows:
>
>
>
>
> Oil Spot Combo #1 (three coats), specific gravity 165
>
>
> Custer Feldspar
>
> 47.83
>
>
> EPK
>
> 10.87
>
>
> Red Iron Oxide
>
> 9.78
>
>
> Silica
>
> 23.91
>
>
> Whiting
>
> 17.39
>
>
>
>
>
>
> Cover Glaze 2 coats
>
>
>
>
> Custer Feldspar
>
> 30
>
>
> Frit 3134
>
> 30
>
>
> Silica
>
> 25
>
>
> Kaolin--EPK
>
> 5
>
>
> Zircopax
>
> 10
>
>
> Total:
>
> 100
>
>
> Copper Carb 4% =3D Green
>
>
>
>
> Cobalt Carb 4% =3D Blue
>
>
>
>
>
>
>
> Robin Wolf
>
>
>
> Robin Wolf Pottery
>
> Kingfisher, OK
>
> www.robinwolfpottery.com
>
--
----------------------------------------------------------
Des & Jan Howard on sat 11 aug 12
Robin
1. Biscuit fire the pot.
2. Dip in glaze.
3. Biscuit fire the pot.
4. Dip in glaze.
5. Glaze fire pot.
Des
On 11/08/2012 8:26 AM, Robin Wolf wrote:
> I am working on Cone 6 oil spot glazes, and am having a terrible time wit=
h
> the application process.
--
Des & Jan Howard
Lue Pottery
Lue NSW
Australia
2850
02 6373 6419
www.luepottery.hwy.com.au
-32.656072 149.840624
William & Susan Schran User on sat 11 aug 12
From: Robert Harris
Date: Friday, August 10, 2012 11:12 PM
To: William & Susan Schran User
Cc:
Subject: Re: Cone 6 Oil Spot Application Pointers Needed
Bill and Robin,
I notice that Bill puts his cracking and flaking at the feet of high
shrinkage zinc oxide, whereas I was suggesting to you that you need to
increase shrinkage.
Both of these problems (too much or too little shrinkage) can lead to
flaking - you'll need to figure out which one. If there is insufficient
shrinkage, the drying glaze layer will seem to lift off the pot, but withou=
=3D
t
necessarily producing cracks in the glaze layer - in fact you can often fee=
=3D
l
blisters forming on a drying pot.
If there is too much shrinkage on the other hand I think you get fissures
forming, and you can feel the glaze layer release from the pot surface, but
not being pushed up from the pot surface like you do if there is
insufficient shrinkage.
Bill does this sound right? I have much less experience with this sort of
cracking.
Robert & Robin,
Sounds about right to me. If I have no gum binder in the glaze the glaze
will crack into fissures and can just peel off. I've also found more
possibilities of crawling from glaze forming fissures as it is heated and
dried.
Just wondering if a lower bisque firing might held =3DE2=3D80=3D93 just thi=
nking out lo=3D
ud=3DE2=3D80=3DA6
Bill
--=3D20
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
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