Paul Taylor on sat 16 dec 00
Dear Craig
I am a pig in muck . I am using a Grolleg body (that Is if the
manufacturers followed the recipe they advertise ) and Norfloat.
I am testing the iron by (temporarily) using iron sulphate from a chemical
suppliers. At least I will not have to grind that . I am hoping a little
early reduction will burn off the sulphur.
And in case you get thinking - I am using distilled water.
It has to be the iron that has changed! but I have a reference to
formula for wolistonite and whitings full of containments so they may be
causing trouble as well ( We are still blaming all this on Maggie Thatcher
and Ronald Ragen) going directly to the quarries would solve all . So I
am testing those two as well in a 80% Norfloat to 20% wolistonite and the
85 feldspar 15% whiting, all plus the soluble iron 2.5 % to see what colors
I get. That should narrow it down. I made this glaze years ago and it worked
then. If you see a howler in the thinking tell me save me a couple of hours
work. Sulphur ?
I use proportional analyses for my glaze calculation Seeger formulas
seemed too much like arithmetic. Although with the proportional analyses you
can have a simultaneous equation or two to solve. I used to put it all on a
spread sheet. Which is great because if you want to make a few changes you
can watch how those changes effect the balance of the glaze with in the
calculation. Then I changed my computer from an Amstrad to an i-mac( The
sales men said I would not have to put coal in the back of the i-mac ) and
have not bothered to set up the formulas for the spreadsheet so I am back
on the calculator but since I do this sort of calculation so rarely and its
not that much work with a calculator I probably will not bother going back
to automation.
I have never seen a shino glaze in a formula, proportionate or Seeger
form -I can convert from one to the other. If you have one I would be
grateful and if any body else has one for that matter as well.
The shino I have is a variation of an old Collin Pearson white recipe
with enough lithium in it to cure Dr Jackel and Hide of all ills. If
lithium does do harm I would like to avoid it . What else can you use to
stop the crazing or is a certain amount acceptable- zinc calcium barium and
boron will just change the glazes into a mucky olive green or maybe not ?.
I have been experimenting with particle size changes I would like to
apply the catalytic effects I am getting from a smaller particle size in the
glaze slop to a shino - again a few ancient formulas would help. I am being
a bit lazy by asking you and all for a formula. I could work one out from
the recipe I use, but I am wondering how much accumulated error I would be
getting allowing for a lithium substitution for soda. Parmalees suggestions
looks like a piece of "dead reckoning" to me. It will have to do if no one
comes up with some formula.
Tests for the celadons will be out on wednesday if you are still interested
Regards from Paul Taylor
http://www.anu.ie/westportpottery
PS Went to Dublin for to see Swan Lake danced by the Stanisslavskie Ballet
traditional and enjoyable (my taste) - had 400 e-mails when I got back.
> From: Craig Martell
> Reply-To: Ceramic Arts Discussion List
> Date: Wed, 13 Dec 2000 20:39:09 -0800
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Re: Shino carbon trap/Paul T.
>
> I tried to make blue celadons for a long time by the empirical method and
> by trying to keep the titanium very low or totally absent from the
> glazes. Never could get a blue celadon. Then I worked with seger formulas
> and current analyses from the mines here and now I can make iron blue
> glazes. The blue celadons are a family of glazes that have some rather
> tight parameters for success. Another thing I found thanks to John Britt
> was that Grolleg porcelains will make the brightest blue celadons. My
> regular porcelain is close to white but has a bit more titanium than is
> good for the blues. I tried a pure Grolleg body and it really livened the
> blue. I'd even used Grolleg slips over my other porcelain to help out but
> it wasn't the same at all. Tricky stuff but I've learned a few things
> which is a good payback too.
>
> If you can get some of that Norwegian potash spar, Norfloat, you'd be right
> in the ballpark for a good blue. That stuff is really high in potassium and
> that is what you want for blue celadons.
>
> regards, Craig Martell in Oregon
Craig Martell on mon 18 dec 00
Paul asked:
>I have never seen a shino glaze in a formula, proportionate or Seeger
>form -I can convert from one to the other. If you have one I would be
>grateful and if any body else has one for that matter as well.
Hello Paul and others:
Here are some shino recipes and the seger formulas. These are from
original flux mixtures that I subjected to Ian Currie recipe biaxials (35
glaze grids). I will give you 4 glazes. Two from one set and two from
another. Two red shinos and two hot orange shinos.
Orange shino #19 cone 10 R
Nepheline syenite 36.31
North Fork Stone 10.38
Spodumene 5.19
Alumina Oxide 14.38
Silica 33.75
K2O 0.341 Al2O3 2.376 SiO2 9.607 Si/Al ratio 4.044/1
Na2O 0.427 P2O5 0.001 TiO2 0.015
Li2O 0.104
CaO 0.070
MgO 0.058
As you can see from the Seger formula, this glaze is way out of the ball
park in terms of cone 10 limits. It has a lot more silica and alumina than
you would expect to see in a glaze that would melt at this
temperature. But it is fused and glassy at cone 10. The iron for color is
supplied by the North Fork Stone which is a glacially ground, stream
transported and levigated basalt stone. In the analysis, NF Stone has
about 8.5% iron so you can take that percentage of the stone in the recipe
and figure the iron. The NF Stone probably contains some Apatite and
Diorite as well. There are some intrusions of this nature upstream from
where I collect the stone.
Red Shino #22 cone 10 R
Nepheline Syenite 53.38
North Fork Stone 15.25
Spodumene 7.63
Alumina Oxide 12.08
Silica 11.67
K2O 0.341 Al2O3 1.829 SiO2 5.764 Si/Al ratio 3.145/1
Na2O 0.427 P2O5 0.001 TiO2 0.015
Li2O 0.104
CaO 0.070
MgO 0.058
These two glazes came out of the same set. If you look at the fluxes in
the Seger Formula, they are exactly the same in both glazes yet one glaze
is red and the other is orange. This is due to the lower silica/alumina
ratio in the red shino. Higher amounts of alumina keep the iron from going
into solution and let it crystalize more and produce the deeper red. There
is also some undisolved silica in glaze #19 which is making this one more
orange.
I realize that none of you have North Fork Stone. I would suggest using
iron bearing slip clays such as Jasper slip or Albany if you have it, also
Cedar Heights Redart would be good. Get as close to the Seger Formulas as
you can and the glazes will most likely work. I've done them on tiles and
pots and they work very well.
This post is a bit long so I'll post the other shinos later if there's an
interest in seeing them. They are a bit more fused and have a different
makeup than most shinos that we see. I think some of them would be good as
low as cone 6.
later, Craig Martell in Oregon
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