Toni Hall on fri 25 oct 96
Clay People,
I am looking for a plain white crackle at cone 04 or 6 oxidation.
I have seen some pieces I believe were done that way, and I have some ideas
I would like to try. I get crackle from my Raku without problems, but I
don't know how to get that finish in an electric kiln. Can someone help me?
Toni
Roeder on sun 27 oct 96
Hi Toni,
I have a cone 5-6 crackle for you:
Cone 5-6 Crackle Glaze
Neph Sy ........................70
Whiting..........................20
6 Tile (Georgia Kaolin) .... 50
Total..............................100
Simple, eh?
Size of crackle varies w/ type of clay body used. I have used it on
porcelain at cone 6 and found it to be a small crackle, and semi-gloss.
Also, looking at the glaze contents, it seems this would take stains very
well. Crackle glazes should not be considered food safe....decorative only.
I have only used it in oxidation, and I do not know what it will look like
in reduction (I imagine it will still be a crackle glaze). I have not used
it over underglazes, but I don't see why not (it's not opacified). You can
rub black india ink (or some other color ink, or paint wash, or stain and
refire...whatever, into the craze lines I suppose). It will continue to
crackle (craze) for a couple days, but does have crackle immediately after
unloading. Not a raku glaze.
Candice Roeder
beautiful fall day in Meeeechigan
At 09:12 PM 10/25/96 +0000, you wrote:
>----------------------------Original message----------------------------
>Clay People,
> I am looking for a plain white crackle at cone 04 or 6 oxidation.
>I have seen some pieces I believe were done that way, and I have some ideas
>I would like to try. I get crackle from my Raku without problems, but I
>don't know how to get that finish in an electric kiln. Can someone help me?
>
>Toni
>
The Allens on sun 20 jul 97
I'm in need of a Cone 6 opaque crackle glaze (oxidation) if anyone has one and d
Thanks in advance,
Carla Allen
ridgerun@scrtc.blue.net
cobalt on sun 2 may 99
Hi,
I'm looking for a cone 5/6 White crackle glaze with a satin matt to gloss
surface.
Does anyone have a recipe they'd be willing to share?
Thanks , Duane
William Moody on sun 29 jul 01
I am looking for a good cone 6 crackle glaze and I am wondering if the =
black in the crackles is caused by reduction or if it is usually a =
rubbed in ink or stain. I have pulled a few out of the archives and I am =
going to start the testing soon. I am using it for an 'oriental' style =
dinner setting and I am fully aware of the supposed health hazards. If =
anyone has any other crackle glazes in the cone 6 or cone 10 range I =
would be very interested in them. thanks in advance
Snail Scott on mon 30 jul 01
At 09:17 PM 7/29/01 -0400, you wrote:
>I am looking for a good cone 6 crackle glaze and I am wondering if the
black in the crackles is caused by reduction >or if it is usually a rubbed
in ink or stain....I am using it for an 'oriental' style dinner setting and
I am fully >aware of the supposed health hazards...
It sounds like you are looking for a raku-style appearance
in stoneware.
In raku, the crackle is largely due to the thermal stresses
of being removed from the kiln while still red-hot. It can
survive this because the clay is not vitrified. (Many
people use stoneware clay for raku becaude it will be even
less vitrified than an earthenware would be, and thus even
more resistant to the thermal shock.) There are additives
to reduce thermal shock in vitrified clay (of the sort used
for stove-top bodies), but I strongly recommend against
using the raku process on matured stoneware. Even if the
ware survives, it will have stress cracks which will make
it much more fragile in use.
You can formulate a glaze which will crackle (craze) on
stoneware, though. It just needs to have a bad fit with
the clay underneath. Which recipes might be best will depend
on your clay body, but recipes which are shy of silica often
craze. Don't get too far out of balance, but if there isn't
much oxide to get released from your glaze, it will probably
be safe enough. I would get input from someone more
knowledgeable than I about possible recipes, though.
On the bright side, the food-safety issues normally associated
with raku crackle stem from the compromised glaze coating,
which allows food and moisture to seep into the porous clay
and breed exciting, friendly microbes seeking a free vacation
in your gut. Vitrified stoneware will not absorb the same way,
and I believe the crackle finish will not cause any significant
increase in the 'biological content' of the finished ware
after use, compared to a normal uncrazed glaze.
In raku, the blackening of the crackle is due to the intense
smoke of the post-firing reduction, (not to be confused with
reduction firing!) which penetrates into the porous, non-
vitrified clay beneath the glaze. A vitrified stoneware will
not absorb smoke, or any of the other 'fake' blackening
processes either. The look of a blackened crackle on a
vitrified surface is different than on a porous one since
it can't spread into the clay and 'feather out'. And, ink or
paint will not last long under dinnerware-washing conditions
even in the cracks, I suspect, even if it was safe to ingest.
Perhaps a bit of black lowfire glaze or china paint could be
forced into the cracks and the ware then refired, but I wonder
if the particle size of these materials is small enough to
really penetrate.
You might want to use the crackle glaze, but skip darkening it.
-Snail
Olivia T Cavy on mon 30 jul 01
There's another way to get a crackle appearance, although I haven't done
enough experiments to get it to work consistently.
If you bisque and apply your ^6 glaze and then refire to a bisque temp
like ^06 very quickly, many glazes will develop cracks.
Because the pots have only been fired to bisque temp and are still
porous, you can re-dip the pot in a contrasting color glaze, and then
fire at normal speed to ^6. The contrasting color glaze ends up in the
fissures of the first glaze, and unless you have very runny glazes, the
whole thing fires looking like a crackle glaze. However after the ^6
firing, the glazes are now mature and texturally solid.
I've done this using Tony Hansen's 5 part glaze, using floating blue
colorants (rutile, cobalt carb and RIO) as my base. It's a midnight blue
color. After the fast fire bisque I dipped the pots in a glossy white
glaze and fired to ^6 at normal speed. I ended up with a finished
appearance that looked like blue marble.
The hard part is figuring how how fast to re-fire to bisque temp so that
the base glaze WILL craze.
Bonnie
Bonnie D. Hellman, Pittsburgh, PA
PA work email: oliviatcavy@juno.com
PA home email: mou10man@sgi.net (that's the number 10 in the middle of
the letters)
CO email: mou10man@rmi.net (that's the number 10 in the middle of the
letters)
On Mon, 30 Jul 2001 09:21:00 -0700 Snail Scott
writes:
> At 09:17 PM 7/29/01 -0400, you wrote:
> >I am looking for a good cone 6 crackle glaze and I am wondering if
> the
> black in the crackles is caused by reduction >or if it is usually a
> rubbed
> in ink or stain....I am using it for an 'oriental' style dinner
> setting and
> I am fully >aware of the supposed health hazards...
>
>
>
> It sounds like you are looking for a raku-style appearance
> in stoneware.
>
> In raku, the crackle is largely due to the thermal stresses
> of being removed from the kiln while still red-hot. It can
> survive this because the clay is not vitrified. (Many
> people use stoneware clay for raku becaude it will be even
> less vitrified than an earthenware would be, and thus even
> more resistant to the thermal shock.) There are additives
> to reduce thermal shock in vitrified clay (of the sort used
> for stove-top bodies), but I strongly recommend against
> using the raku process on matured stoneware. Even if the
> ware survives, it will have stress cracks which will make
> it much more fragile in use.
>
> You can formulate a glaze which will crackle (craze) on
> stoneware, though. It just needs to have a bad fit with
> the clay underneath. Which recipes might be best will depend
> on your clay body, but recipes which are shy of silica often
> craze. Don't get too far out of balance, but if there isn't
> much oxide to get released from your glaze, it will probably
> be safe enough. I would get input from someone more
> knowledgeable than I about possible recipes, though.
>
> On the bright side, the food-safety issues normally associated
> with raku crackle stem from the compromised glaze coating,
> which allows food and moisture to seep into the porous clay
> and breed exciting, friendly microbes seeking a free vacation
> in your gut. Vitrified stoneware will not absorb the same way,
> and I believe the crackle finish will not cause any significant
> increase in the 'biological content' of the finished ware
> after use, compared to a normal uncrazed glaze.
>
> In raku, the blackening of the crackle is due to the intense
> smoke of the post-firing reduction, (not to be confused with
> reduction firing!) which penetrates into the porous, non-
> vitrified clay beneath the glaze. A vitrified stoneware will
> not absorb smoke, or any of the other 'fake' blackening
> processes either. The look of a blackened crackle on a
> vitrified surface is different than on a porous one since
> it can't spread into the clay and 'feather out'. And, ink or
> paint will not last long under dinnerware-washing conditions
> even in the cracks, I suspect, even if it was safe to ingest.
> Perhaps a bit of black lowfire glaze or china paint could be
> forced into the cracks and the ware then refired, but I wonder
> if the particle size of these materials is small enough to
> really penetrate.
>
> You might want to use the crackle glaze, but skip darkening it.
>
> -Snail
>
>
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