ken tighe on wed 29 oct 97
First the recipe: Neph Sy 16, Whiting 20, Gerstley borate 21, Kaolin 11,
silica 32, tin 5, chrome 0.15. (cone 6 oxid.)
I well understand why this beautiful glaze is so popular. But for me
it crawls. Indeed it often falls off large portions of some of my pots
making pretty puddles on the shelf. (I use a white stoneware clay-- Miller
65). I wrote to Brian Kemp about it a while back and he suggested I take a
reliable base glaze of my own, then add the tin and chrome in the
appropriate ratio. Well, that's what I've been about to do. Then I
noticed the recent discussion about the glaze by Liz Dodge and others so I
thought I'd let a question fly.
John Post tested this glaze recently. In his post of 10/27/97 he
said, "It was rather runny on my stoneware body." I was wondering if
anyone had problems similar to mine. Thanks , Ken.
John Post on thu 30 oct 97
> ----------------------------Original message----------------------------
> First the recipe: Neph Sy 16, Whiting 20, Gerstley borate 21, Kaolin 11,
> silica 32, tin 5, chrome 0.15. (cone 6 oxid.)
> I well understand why this beautiful glaze is so popular. But for me
> it crawls. Indeed it often falls off large portions of some of my pots
> making pretty puddles on the shelf. (I use a white stoneware clay-- Miller
> 65). I wrote to Brian Kemp about it a while back and he suggested I take a
> reliable base glaze of my own, then add the tin and chrome in the
> appropriate ratio. Well, that's what I've been about to do.
>Then I
> noticed the recent discussion ... I was wondering if
> anyone had problems similar to mine. Thanks , Ken.
Ken,
I think the problem you are having is related to the lack of alumina
and silica in the glaze. The unity formula for Kemp 17 shows the
alumina at .23 which is at the low end of the limit formula that I
use (.2-.35). The silica at 2.30 is also under what I shoot for in a
cone 6 glaze (2.5 - 3.5). It's my belief that this glaze is
overfluxed which is why it is too runny on my stoneware body and
probably why it jumps off of your pots.
Kemp 17 unity...
Na2O 0.13 Al2O3 0.23 SiO2 2.30
K2O 0.02 B2O3 0.25 Cr2O3 0.00
MgO 0.05 SnO2 0.09
CaO 0.80
In my original post about Kemp 17 I mentioned that I mixed
it with another Kemp glaze that was too mat and came up with a nice
stable pink (PMSP1). If we look at the unity formula for that glaze
you can see how the alumina and silica fall within the range of the
limit formula that I use.
Unity for PMSP-1
Na2O 0.17 Al2O3 0.32 SiO2 3.16
K2O 0.04 B2O3 0.15 Cr2O3 0.01
MgO 0.03 SnO2 0.17
CaO 0.76
(you might also notice that the CaO is high in both of the glazes and
that helps contribute to the nice pink color as well)
for those who might have missed the first posting here is the recipe
for
PMSP 1 Base (Cranberry Variation) Cone 5-6 oxidation
10.5 Gerstley borate
25 Nepheline syenite
36.5 Flint
18.5 Whiting
9.5 EPK
100 %
Add:
7.5 Tin oxide
0.325 Green chrome oxide
Since PMSP1 is already well balanced maybe you could just try
this as a base using various percentages of tin and chrome. If you
want to stay away from the gerstley borate then you could try the
PMSP3 that I mentioned in the previous post.
I have found that the materials that go into the base glaze do affect
the way the tin and the chrome react. Even though PMSP1 and PMSP3
are very similar in terms of unity formula, they are different in
terms of color response. The PMSP1 tends to go more cranberry pink,
while the PMSP3 tends to go more towards the purple family.
I still use Kemp 17. I use it near the rims on pots where I know it
will flow down in wonderful swirls of purples and crimsons over my
base glazes.
I hope this helps...
John Post
email: rp1mrvl@moa.net
Marni Turkel on fri 31 oct 97
A few months ago I tested Kemp 17, and added 5% extra tin so that it was
not so transparent. It lost some of its brilliance and a bit of its gloss,
but was still very nice. I fire to c5. Since then I have mixed several
batches that worked very well. Recently I have had problems with crawling.
The first batches were mixed with a fairly fine grind of tin that I buy
from Laguna Clay. I ran out of that and substituted a coarse grind that I
buy locally, that also worked fine. The last batch mixed used a new batch
of fine ground tin, and I've been having trouble with small patches of
crawling on many pieces. I can't swear that no other material was from a
different batch, but I'm planning to remix with coarse tin and see if that
solves my problem.
Marni Turkel
Ken Tighe wrote:
>First the recipe: Neph Sy 16, Whiting 20, Gerstley borate 21, Kaolin 11,
>silica 32, tin 5, chrome 0.15. (cone 6 oxid.)
> I well understand why this beautiful glaze is so popular. But for me
>it crawls. Indeed it often falls off large portions of some of my pots
>making pretty puddles on the shelf. (I use a white stoneware clay-- Miller
>65). I wrote to Brian Kemp about it a while back and he suggested I take a
>reliable base glaze of my own, then add the tin and chrome in the
>appropriate ratio. Well, that's what I've been about to do. Then I
>noticed the recent discussion about the glaze by Liz Dodge and others so I
>thought I'd let a question fly.
> John Post tested this glaze recently. In his post of 10/27/97 he
>said, "It was rather runny on my stoneware body." I was wondering if
>anyone had problems similar to mine.
Marni Turkel
Stony Point Ceramic Design
Sonoma County, California
LizzardOL on fri 31 oct 97
I don't know why Kemp 17 is crawling on Ken's pots, but i've never had that
problem. That makes me think it isn't fitting your clay body, although I've
also used it on a white stoneware (laguna B-mix cone 10) that was bisqued to
06 and fired to ^6 in an electric kiln.
liz dodge in Berkeley, CA
In a message dated 10/29/97 1:54:10 PM, ktighe@capecod.net wrote:
<silica 32, tin 5, chrome 0.15. (cone 6 oxid.)
I well understand why this beautiful glaze is so popular. But for me
it crawls. Indeed it often falls off large portions of some of my pots
making pretty puddles on the shelf. (I use a white stoneware clay-- Miller
65). I wrote to Brian Kemp about it a while back and he suggested I take a
reliable base glaze of my own, then add the tin and chrome in the
appropriate ratio. Well, that's what I've been about to do. Then I
noticed the recent discussion about the glaze by Liz Dodge and others so I
thought I'd let a question fly.
John Post tested this glaze recently. In his post of 10/27/97 he
said, "It was rather runny on my stoneware body." I was wondering if
anyone had problems similar to mine. Thanks , Ken.
>>
Craig Martell on sat 1 nov 97
I think that the crawling problem is related to the high zinc content in
this glaze. If the zinc is calcined, the problem may be greatly minimized
or eliminated.
regards, Craig Martell-Oregon
Peggy Heer on sat 1 nov 97
Hi Liz....how can you use a cone 10 clay and fire it to cone 6 and sell it
as a usable piece? It would not be water proof etc as the clay would not
be vitrified unless you are making work that does not require this......do
others use a cone 10 and glaze fire to ^6 and sell as vitrified work? Just
wondering. Happy Halloween everyone.
As Always in Clay Peggy
-----------------------------------------------
although I've
>also used it on a white stoneware (laguna B-mix cone 10) that was bisqued to
>06 and fired to ^6 in an electric kiln.
>
>liz dodge in Berkeley, CA
Peggy Heer / Heer Pottery E-Mail p4337@connect.ab.ca
52120 Range Road 223
Sherwood Park, AB. Canada T8C 1A7
Phone (403) 922-6270
http://www.ffa.ucalgary.ca/artists/pheer/
Liz Dodge on sun 2 nov 97
HI PEGGY
I usually fire functional ware to cone 10, so I don't know actual scientific
answer to your question. But it seems like if the glaze melts and stays on
the pot, the pot ought to be reasonably waterproof. Maybe I'll find that
vase with the Kemp 17 on it and fill it with water and see what happens.
I'll keep you posted.
Liz Dodge in Berkeley, CA
In a message dated 11/1/97 11:12:34 PM, you wrote:
<as a usable piece? It would not be water proof etc as the clay would not
be vitrified unless you are making work that does not require this......do
others use a cone 10 and glaze fire to ^6 and sell as vitrified work? Just
wondering. Happy Halloween everyone.
As Always in Clay Peggy
-----------------------------------------------
although I've
>also used it on a white stoneware (laguna B-mix cone 10) that was bisqued to
>06 and fired to ^6 in an electric kiln.
>
>liz dodge in Berkeley, CA
Peggy Heer / Heer Pottery E-Mail p4337@connect.ab.ca
52120 Range Road 223
Sherwood Park, AB. Canada T8C 1A7
Phone (403) 922-6270
http://www.ffa.ucalgary.ca/artists/pheer/
>>
Kris Baum on tue 4 nov 97
I, too, am curious. I've used a ^04 low-fire body for tiles - porous
at that temperature - and taken it up as high as ^6 with no visible
change - still extremely porous - it sucks up the glaze like you
wouldn't believe. My ^6 body is nicely vitrified at ^6. Maybe the
labeled cone isn't a true indication of where that clay body will
vitrify?
> ----------------------------Original message----------------------------
> Hi Liz....how can you use a cone 10 clay and fire it to cone 6 and sell it
> as a usable piece? It would not be water proof etc as the clay would not
> be vitrified unless you are making work that does not require this......do
> others use a cone 10 and glaze fire to ^6 and sell as vitrified work? Just
> wondering. Happy Halloween everyone.
> As Always in Clay Peggy
> -----------------------------------------------
> although I've
> >also used it on a white stoneware (laguna B-mix cone 10) that was bisqued to
> >06 and fired to ^6 in an electric kiln.
> >
> >liz dodge in Berkeley, CA
>
> Peggy Heer / Heer Pottery E-Mail p4337@connect.ab.ca
> 52120 Range Road 223
> Sherwood Park, AB. Canada T8C 1A7
> Phone (403) 922-6270
> http://www.ffa.ucalgary.ca/artists/pheer/
>
>
===============================================
Kris Baum, Shubunkin Pottery
mailto:shubunki@erols.com
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