David Hendley on thu 26 feb 98
For a food safe black I would use a tenmoku.
Here's one I've used for years.
Perhaps Ron Roy (aka 'Mr. Tenmoku') will comment as
to whether he would consider this glaze food safe.
Seacrest Tenmoku ^10 reduction
Custer feldspar 54
Whiting 13
Barium Carbonate 2.5
Zinc oxide 2.5
Kaolin 6
Flint 22.5
Red iron oxide 5
This glaze will definately produce black where thick, brown where
thin, but it is really quite a differnt look from the 'Albany slip loaded
with metallic oxides' type glazes. Those glazes 'look' metallic, and there
is no color variation - always black.
A tenmoku, by contrast, will be affected by variables such as glaze
thickness and kiln atmoshpere. Actually, a much more expressive glaze,
allowing you to highlight nuances of the clay underneath.
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
At 10:07 AM 2/25/98 EST, you wrote:
>----------------------------Original message----------------------------
>Hi David,
> What black ^10 glaze would you recommend to be food safe
>then, or do you just not recommend any at all?
>
>Thanks
>Bjorn
>
>
>Date: Fri, 20 Feb 1998 08:22:27 EST
>From: David Hendley
>Subject: Albany Slip substitute
>
>
>My Modified Rhodes Black ^10
>
>Minspar (soda) feldspar 57
>EPK 9
>Redart 25
>Dolomite 6.5
>Whiting 2.5
>Red Iron ox 5
>Manganese Diox 3.7
>Cobalt ox 1.3
> 110
>
>This glaze is well balanced and has plenty of silica, but
>with all those metals, I don't use it on food surfaces.
>
Craig Martell on fri 27 feb 98
At 07:46 AM 2/26/98 EST, David Hendley wrote:
>----------------------------Original message----------------------------
>For a food safe black I would use a tenmoku.
>Here's one I've used for years.
>Perhaps Ron Roy (aka 'Mr. Tenmoku') will comment as
>to whether he would consider this glaze food safe.
>
>Seacrest Tenmoku ^10 reduction
>
>Custer feldspar 54
>Whiting 13
>Barium Carbonate 2.5
>Zinc oxide 2.5
>Kaolin 6
>Flint 22.5
>
>Red iron oxide 5
David:
Sorry to butt in, I know I'm not "Mr. Tenmoku", but I had a question and a
comment about this glaze. It's actually a very well balanced glaze with
lots of silica but I was wondering about the barium and zinc. There has
been a lot of discussion about the worthlessness of zinc in high fire
reduction, and that it contributes nothing at all to the glazes. Also, why
the small amount of barium? How does it benefit the glaze? Most good
tenmokus are blends of feldspar and limestone with silica and alumina. You
get the good black-rust color without the zinc and barium. I guess that I
could answer my own question by running tests of this base but I just
wondered if you had any insight as to the value of these two materials. I
would be tempted to delete the zinc and barium and put the extra percentage
into the spar and whiting.
I agree very much with your comment about tenmokus being more expressive
than glazes that are loaded with metals to make them black. Tenmokus are
fine for food use too, as you stated. Warren Mackenzie told me once that he
preferred tenmokus above all other glazes for dinner plates because food
looked so good on this type of glaze. I sold some black tenmoku plates to a
chef at the Park City Art Festival some time back and he said the same thing.
regards, Craig Martell-Oregon
David Hendley on sun 1 mar 98
>I was wondering about the barium and zinc. There has
>been a lot of discussion about the worthlessness of zinc in high fire
>reduction, and that it contributes nothing at all to the glazes. Also, why
>the small amount of barium? How does it benefit the glaze?
=======================================
My thoughts exactly, about the barium and zinc, Craig.
I don't know, but I have a feeling that the glaze would be
just as good without either one, especially since there is
such a small amount of each.
I make a point of sending to Clayart only glazes that have
proven reliable over the years. This is the recipe I got in
school before I could even do a glaze calculation. I know
that it is a durable glaze that has held up on dishes I've been
using for 20 years or more.
As you know, there is disagreement about the value of zinc
oxide in a high fire reduction glaze. Some highly regarded
authors attribute benefits to small additions of zinc oxide in
a high fire reduction glaze. Others contend that all the zinc
is volitalized, and adds absoulutely nothing to the glaze.
I think it is generally agreed that using several different fluxes
in a glaze can be desirable. It can help to form eutetics, and can widen
the firing range of the glaze. Perhaps the barium carbonate serves
some function along these lines, and that's why the author of the
glaze added it into the recipe?
I have not ever done research aimed at formulating tenmoku
glazes, but I know a good tenmoku can be formulated using only
feldspar, whiting, clay, flint, and iron oxide. I also think (emphisize
'think', I haven't set out to test it) that most any good celadon glaze
will make a reasonably good tenmoku simply by incresing it's iron content.
An area that I am interested in, and have been researching, is
copper red glazes. A majority of the copper red glaze recipes I've
seen through the years include both zinc oxide and barium carbonate
in their recipes, again both in small percentages, and I wondered why.
I think it perhaps dates back to 1888 when C. Lauth & G. Dutailly wrote
"Research on Copper Reds and Celadons", one of the first scientific
studies of copper red glazes. The article, reprinted in Tichane's 'copper
reds' book, says that 'zinc associated with barium gives the
most beautiful reds.'
I have been testing variations of my copper red glaze with and
without zinc oxide, with and without Barium carbonate, and with
strontium carbonate replacing the barium carbonate.
I don't want to state any conclusions until I can work with the different
variations over the course of many firings, but so far, I can't see any
benefit added by zinc, barium, or strontium in small amounts.
My tests are purely subjective, looking for nuances of color development,
not technical qualities of the glazes.
How 'bout it? Do some similar tests in the tenmoku department
and you, too, could be a 'Mr. Tenmoku'.
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
>At 07:46 AM 2/26/98 EST, David Hendley wrote:
>>----------------------------Original message----------------------------
>>For a food safe black I would use a tenmoku.
>>Here's one I've used for years.
>>Perhaps Ron Roy (aka 'Mr. Tenmoku') will comment as
>>to whether he would consider this glaze food safe.
>>
>>Seacrest Tenmoku ^10 reduction
>>
>>Custer feldspar 54
>>Whiting 13
>>Barium Carbonate 2.5
>>Zinc oxide 2.5
>>Kaolin 6
>>Flint 22.5
>>
>>Red iron oxide 5
>
>David:
>
>Sorry to butt in, I know I'm not "Mr. Tenmoku", but I had a question and a
>comment about this glaze. It's actually a very well balanced glaze with
>lots of silica but I was wondering about the barium and zinc. There has
>been a lot of discussion about the worthlessness of zinc in high fire
>reduction, and that it contributes nothing at all to the glazes. Also, why
>the small amount of barium? How does it benefit the glaze? Most good
>tenmokus are blends of feldspar and limestone with silica and alumina. You
>get the good black-rust color without the zinc and barium. I guess that I
>could answer my own question by running tests of this base but I just
>wondered if you had any insight as to the value of these two materials. I
>would be tempted to delete the zinc and barium and put the extra percentage
>into the spar and whiting.
>
>I agree very much with your comment about tenmokus being more expressive
>than glazes that are loaded with metals to make them black. Tenmokus are
>fine for food use too, as you stated. Warren Mackenzie told me once that he
>preferred tenmokus above all other glazes for dinner plates because food
>looked so good on this type of glaze. I sold some black tenmoku plates to a
>chef at the Park City Art Festival some time back and he said the same thing.
>
>regards, Craig Martell-Oregon
>
>
Stephen Mills on mon 2 mar 98
On the Tenmoku front the recipes we used at college (there were 2) were
as simple as David mentions. my favourite, attributed to Henry Hammond,
is: (parts by weight)
potash feldspar....67
whiting............12
china clay.........12
flint...............9
red iron oxide......9
This was the original recipe, on a light or white clay in heavy
reduction it's a corker, however if used on an iron bearing clay the
iron oxide will have to be reduced or you get a saturated iron (reddish)
glaze, as I found out the hard way ('till the iron imbalance was pointed
out to me)
Steve
Bath
UK
In message , David Hendley writes
>----------------------------Original message----------------------------
>>I was wondering about the barium and zinc. There has
>>been a lot of discussion about the worthlessness of zinc in high fire
>>reduction, and that it contributes nothing at all to the glazes. Also, why
>>the small amount of barium? How does it benefit the glaze?
>=======================================
>
>My thoughts exactly, about the barium and zinc, Craig.
>I don't know, but I have a feeling that the glaze would be
>just as good without either one, especially since there is
>such a small amount of each.
>
>I make a point of sending to Clayart only glazes that have
>proven reliable over the years. This is the recipe I got in
>school before I could even do a glaze calculation. I know
>that it is a durable glaze that has held up on dishes I've been
>using for 20 years or more.
>
>As you know, there is disagreement about the value of zinc
>oxide in a high fire reduction glaze. Some highly regarded
>authors attribute benefits to small additions of zinc oxide in
>a high fire reduction glaze. Others contend that all the zinc
>is volitalized, and adds absoulutely nothing to the glaze.
>
>I think it is generally agreed that using several different fluxes
>in a glaze can be desirable. It can help to form eutetics, and can widen
>the firing range of the glaze. Perhaps the barium carbonate serves
>some function along these lines, and that's why the author of the
>glaze added it into the recipe?
>
>I have not ever done research aimed at formulating tenmoku
>glazes, but I know a good tenmoku can be formulated using only
>feldspar, whiting, clay, flint, and iron oxide. I also think (emphisize
>'think', I haven't set out to test it) that most any good celadon glaze
>will make a reasonably good tenmoku simply by incresing it's iron content.
>
>An area that I am interested in, and have been researching, is
>copper red glazes. A majority of the copper red glaze recipes I've
>seen through the years include both zinc oxide and barium carbonate
>in their recipes, again both in small percentages, and I wondered why.
>I think it perhaps dates back to 1888 when C. Lauth & G. Dutailly wrote
> "Research on Copper Reds and Celadons", one of the first scientific
>studies of copper red glazes. The article, reprinted in Tichane's 'copper
>reds' book, says that 'zinc associated with barium gives the
>most beautiful reds.'
>I have been testing variations of my copper red glaze with and
>without zinc oxide, with and without Barium carbonate, and with
>strontium carbonate replacing the barium carbonate.
>I don't want to state any conclusions until I can work with the different
>variations over the course of many firings, but so far, I can't see any
>benefit added by zinc, barium, or strontium in small amounts.
>My tests are purely subjective, looking for nuances of color development,
>not technical qualities of the glazes.
>
>How 'bout it? Do some similar tests in the tenmoku department
>and you, too, could be a 'Mr. Tenmoku'.
>
>David Hendley
>Maydelle, Texas
>See David Hendley's Pottery Page at
>http://www.sosis.com/hendley/david/
>
>
>
>>At 07:46 AM 2/26/98 EST, David Hendley wrote:
>>>----------------------------Original message----------------------------
>>>For a food safe black I would use a tenmoku.
>>>Here's one I've used for years.
>>>Perhaps Ron Roy (aka 'Mr. Tenmoku') will comment as
>>>to whether he would consider this glaze food safe.
>>>
>>>Seacrest Tenmoku ^10 reduction
>>>
>>>Custer feldspar 54
>>>Whiting 13
>>>Barium Carbonate 2.5
>>>Zinc oxide 2.5
>>>Kaolin 6
>>>Flint 22.5
>>>
>>>Red iron oxide 5
>
>>
>>David:
>>
>>Sorry to butt in, I know I'm not "Mr. Tenmoku", but I had a question and a
>>comment about this glaze. It's actually a very well balanced glaze with
>>lots of silica but I was wondering about the barium and zinc. There has
>>been a lot of discussion about the worthlessness of zinc in high fire
>>reduction, and that it contributes nothing at all to the glazes. Also, why
>>the small amount of barium? How does it benefit the glaze? Most good
>>tenmokus are blends of feldspar and limestone with silica and alumina. You
>>get the good black-rust color without the zinc and barium. I guess that I
>>could answer my own question by running tests of this base but I just
>>wondered if you had any insight as to the value of these two materials. I
>>would be tempted to delete the zinc and barium and put the extra percentage
>>into the spar and whiting.
>>
>>I agree very much with your comment about tenmokus being more expressive
>>than glazes that are loaded with metals to make them black. Tenmokus are
>>fine for food use too, as you stated. Warren Mackenzie told me once that he
>>preferred tenmokus above all other glazes for dinner plates because food
>>looked so good on this type of glaze. I sold some black tenmoku plates to a
>>chef at the Park City Art Festival some time back and he said the same thing.
>>
>>regards, Craig Martell-Oregon
>>
>>
>
--
Steve Mills
Bath
UK
home e-mail: stevemills@mudslinger.demon.co.uk
work e-mail: stevemills@bathpotters.demon.co.uk
own website: http://www.mudslinger.demon.co.uk
BPS website: http://www.bathpotters.demon.co.uk
rballou@mnsinc.com on tue 3 mar 98
>----------------------------Original message----------------------------
>>I was wondering about the barium and zinc. There has
>>been a lot of discussion about the worthlessness of zinc in high fire
>>reduction, and that it contributes nothing at all to the glazes. Also, why
>>the small amount of barium? How does it benefit the glaze?
>=======================================
>
>My thoughts exactly, about the barium and zinc, Craig.
>I don't know, but I have a feeling that the glaze would be
>just as good without either one, especially since there is
>such a small amount of each.
David,
I've wondered also about small amounts of barium. I have one glaze where it
does make a difference. It is a blue glaze with some cobalt, rutile and
iron in it. The color changes dramatically (for the worse, of course) if I
leave out the 2.5% Barium. My copper red also has a little barium and zinc.
The only difference I've noticed by leaving out the zinc is a positive one.
The glaze no longer has a problem with pitting and crawling. I'm not so
sure about leaving out the barium. Copper reds have so many other variables
to consider, firing, etc. that I've been paying more attention to those
than the barium. Perhaps a line blend where the barium is increased to the
point a definite effect shows?
>
>I think it is generally agreed that using several different fluxes
>in a glaze can be desirable. It can help to form eutetics, and can widen
>the firing range of the glaze. Perhaps the barium carbonate serves
>some function along these lines, and that's why the author of the
>glaze added it into the recipe?
Currie's book has quite a bit on high iron glazes. He states that the
barium acts in a similar way as calcium by keeping the iron in solution
which would favor a temmoku as opposed to crystallizing for a kaki or
tessha. Whether and under what conditions the barium is superior or adds to
calcium is up for testing. Then there's the firing and cooling to consider,
too.
Ruth Ballou
rballou@mnsin.com
Silver Spring, MD
| |
|
