Dave Finkelnburg on wed 11 oct 06
Eric,
Thanks for the update!
I agree with Vince that having the soluble flux
migrate to the surface is critical to how American
"Shino" glazes trap carbon.
I have to ask where your information comes from,
though, that sodium has more affinity for carbon than
anything else. I can get carbon trapping with a glaze
with no sodium at all. Just takes enough reduction to
make soot in the kiln and hold it until the glaze
melts and seals the carbon in. Vince's description of
the process is spot on.
Vince is wrong about pearl ash solubility. Pearl
ash is much MORE soluble in water than soda ash. See
the first paragraph under USES at this website.
http://www.ercoworldwide.com/products_potassiumcarbonate.asp
It is a fact that if you use potassium instead of
sodium the glaze will melt and seal over at a somewhat
higher temperature. You need to hold heavy reduction
to a higher temperature using pearl ash. Either you
didn't do that or, as Vince suggests, you didn't get
enough potassium on the glaze surface during the
drying process.
I'm not sure why you got a dry glaze surface. A
draw trial at peak firing temperature might be
helpful.
Good glazing,
Dave Finkelnburg
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
Hank Murrow on wed 11 oct 06
I like this explanation from Dave, and it made me remember that the
Aussies tend to use salt in their shinos rather than soda ash. May be
worth a try.
Cheers, Hank
PS: gave my illustrated talks(parts l and ll), "On the Shino Trail in
Japan" to two receptive audiences in Eugene, and garnered some very
nice reviews for it afterwards. Think I will record a narration so I
can burn a CD or DVD to share it with folks.
On Oct 11, 2006, at 10:20 AM, Dave Finkelnburg wrote:
> Eric,
> Thanks for the update!
> I agree with Vince that having the soluble flux
> migrate to the surface is critical to how American
> "Shino" glazes trap carbon.
> I have to ask where your information comes from,
> though, that sodium has more affinity for carbon than
> anything else. I can get carbon trapping with a glaze
> with no sodium at all. Just takes enough reduction to
> make soot in the kiln and hold it until the glaze
> melts and seals the carbon in. Vince's description of
> the process is spot on.
> Vince is wrong about pearl ash solubility. Pearl
> ash is much MORE soluble in water than soda ash. See
> the first paragraph under USES at this website.
> http://www.ercoworldwide.com/products_potassiumcarbonate.asp
> It is a fact that if you use potassium instead of
> sodium the glaze will melt and seal over at a somewhat
> higher temperature. You need to hold heavy reduction
> to a higher temperature using pearl ash. Either you
> didn't do that or, as Vince suggests, you didn't get
> enough potassium on the glaze surface during the
> drying process.
> I'm not sure why you got a dry glaze surface. A
> draw trial at peak firing temperature might be
> helpful.
> Good glazing,
> Dave Finkelnburg
>
>
> __________________________________________________
> Do You Yahoo!?
> Tired of spam? Yahoo! Mail has the best spam protection around
> http://mail.yahoo.com
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
www.murrow.biz/hank
Des & Jan Howard on thu 12 oct 06
Hank
The 2 shinos we use have the same recipe,
soda feldspar 76.47
clay ceram (local kaolin) 14.71
calc. alumina 8.82
Na2O 0.95 Al2O3 1.00 SiO2 3.59
K2O 0.01 TiO2 0.01
MgO 0.01 Fe2O3 0.01
CaO 0.03
One has a 3% salt addition & the other 15%.
C11 1/2 - 12 1/2
The alumina content makes it somewhat late in melting,
carbon trap is not a usual occurrence, though, a trace has appeared
on pots in a small dead area near one wall of the kiln.
We have tried the fave soda ash/carb shinos & didn't care for the
caramel sauce colours we got. Red/orange/white are our prefs.
Des
Hank Murrow wrote:
> I like this explanation from Dave, and it made me remember that the
> Aussies tend to use salt in their shinos rather than soda ash. May be
> worth a try.
--
Des & Jan Howard
Lue Pottery
LUE NSW 2850
Australia
Ph/Fax 02 6373 6419
http://www.luepottery.hwy.com.au
Lee Love on thu 12 oct 06
On 10/12/06, Des & Jan Howard wrote:
> Hank
> The 2 shinos we use have the same recipe,
> soda feldspar 76.47
> clay ceram (local kaolin) 14.71
Des,
Something I found in my kil: it cycles throught
ox/neut/reduction. When you don't have heavy continuous reduction,
like the atmospheres you would find in the original shino kilns, you
rely on less iron and more alumina in the shinos.
Euan and I discovered this independently firing the same
design kiln. When I mentioned it to Euan, he said, "Sure, ever
notice the reddest things in the kiln are the kiln posts? What are
they made of? Alumina!"
I fire high alumina shinos and he fires a clay body
that is 70% austrailian porcelain and 30% shigaraki nami clay
(standard stoneware), unglazed. You can see my new shino here:
http://potters.blogspot.com/
Euan's unglazed body here:
http://www.d1.dion.ne.jp/~euan/sub4.htm
The high alumina shinos (original shinos) don't carbon trap.
--
Lee in Mashiko, Japan
http://potters.blogspot.com/
"Let the beauty we love be what we do." - Rumi
"When we all do better. We ALL do better." -Paul Wellstone
Eric Newman on fri 13 oct 06
On Wed, 11 Oct 2006 10:20:57 -0700, Dave Finkelnburg
wrote:
>Eric,
> Thanks for the update!
> I agree with Vince that having the soluble flux
>migrate to the surface is critical to how American
>"Shino" glazes trap carbon.
> I have to ask where your information comes from,
>though, that sodium has more affinity for carbon than
>anything else. I can get carbon trapping with a glaze
>with no sodium at all. Just takes enough reduction to
>make soot in the kiln and hold it until the glaze
>melts and seals the carbon in. Vince's description of
>the process is spot on.
> Vince is wrong about pearl ash solubility. Pearl
>ash is much MORE soluble in water than soda ash. See
>the first paragraph under USES at this website.
>http://www.ercoworldwide.com/products_potassiumcarbonate.asp
> It is a fact that if you use potassium instead of
>sodium the glaze will melt and seal over at a somewhat
>higher temperature. You need to hold heavy reduction
>to a higher temperature using pearl ash. Either you
>didn't do that or, as Vince suggests, you didn't get
>enough potassium on the glaze surface during the
>drying process.
> I'm not sure why you got a dry glaze surface. A
>draw trial at peak firing temperature might be
>helpful.
> Good glazing,
> Dave Finkelnburg
>
>
>__________________________________________________
>Do You Yahoo!?
>Tired of spam? Yahoo! Mail has the best spam protection around
>http://mail.yahoo.com
>
>__________________________________________________________________________
____
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
Hey Dave,
Thanks for the post. Here is my source (and granted, just because it is
in print doesn't make it true): "In a reduction atmosphere, a clay
surface streaked with soda may appear glossy and a black-orange in color.
The black color results from the unique attraction of soda to the carbon
particles in the reduction atmosphere, which it traps within the glossy
surface layer. This special "carbon trap" quality of soda is important to
many glaze surfaces." Out of the Earth; Into the Fire, 2nd ed. by Mimi
Obstler.
But something else she mentions in another chapter may explain my lack of
trapping in my substitution of pearl ash for soda ash....the initial
melting of potash is lower (1291 cf. to 1652) than soda, even tho' soda is
a stronger melter. Maybe my start of body redux at a soft 010 is too late
for carbon to be trapped by the potassium carbonate.
Eric
Ivor and Olive Lewis on sat 14 oct 06
Dear Eric Newman,=20
I asked about the nature of this affinity of Soda for Carbon saying that =
I could find no record in CRC for Sodium or Potassium Carbides whitey =
might be considered analogues of Calcium Carbide. I have just checked =
with Kaye and Laby and offer their information about melting points. =
That of Sodium Carbonate is cited as being 851 deg C, that of Potassium =
Carbonate as 891 deg C.
I am curious to know what a "Strong Melter" is. Can you describe this =
characteristic. Or is your source speaking of aggressive solvent =
activity.=20
As I understand the Carbon Trap process, it is important to precipitate =
free carbon prior to melting any other ingredient. If, during drying, =
some of the Sodium or Potassium carbonate is drying on the surface the =
mixture of ingredients is behaving like Egyptian Paste. Should Chlorides =
of either of these metals be present they will melt before the =
carbonates. NaCl at 801 deg C and KCl at 776 deg C.
| |
|
