Marshall on mon 9 nov 98
the nicest bright oranges are iron and i have seen a few good ones, but
have yet to make one myself. ox. or red. cone ten recipies are welcome. i
belive bone ash as one of the sources of calcium helps plus possibly small
amounts of barium. i am looking for a calcium base i think but to compare a
few of your tested glazes on the computer before i formulate will
help...results posted annon
Maggie Woodhead on wed 11 nov 98
A Janet De Boos recipe for the electric kiln to cone 10
50-Soda feldspar
7-Ball clay
6.5-Calcite
6-Talc
10.5-Bone ash
20-Silica
A bright red used extensively here, we call it tomato red, it has a nice
glow and responds well to overglazing with ash glazes or high
feldspathic glazes.
----Best Wishes Maggie----
maggie@clear.net.nz
Leo Smith on fri 13 nov 98
>----------------------------Original message----------------------------
>A Janet De Boos recipe for the electric kiln to cone 10
>
>50-Soda feldspar
>7-Ball clay
>6.5-Calcite
>6-Talc
>10.5-Bone ash
>20-Silica
>
>A bright red used extensively here, we call it tomato red, it has a nice
>glow and responds well to overglazing with ash glazes or high
>feldspathic glazes.
>
>----Best Wishes Maggie----
> maggie@clear.net.nz
To be a bright red it needs 8-10% Fe2O3. This is a variant of the Shiga
Shigeo Tomato Red a very common glaze in Japan. It is very variable and
is best with a soak or slow cooling to develop crystals. In this form,
without the Iron you get a milky glaze that give a bright red responce to
iron brush work (Especially in reduction) It is a very stable glaze.
Best Wishes
Leo Smith
leothelion@bigfoot.com
Maggie Woodhead on sat 14 nov 98
Dear Bonnie! Thank you, for pointing this out, of course there is an
oxide and it is 10% Red iron Oxide which gives the best colour.
What a silly mistake!! Sincere apologies all round!
However the redness of the glaze is affected by the colour of the
clay over which it is used. It really does give a good warm red.
----Best Wishes Maggie----
maggie@clear.net.nz
Best of luck!
----Best Wishes Maggie----
maggie@clear.net.nz
Ron Roy on sat 14 nov 98
This is interesting - when I calculate this glaze for an oxidation firing
it looks like a durable glaze - even with 10% iron added.
If I include the iron as a flux - read reduction firing - then it is
seriuosly short of silica.
The question now becomes - how do we know it is a stable glaze when fired
in reduction with 10% RIO.
If I calculate with 8% RIO the situation looks a bit better but still short
of silica.
Does anyone know if it stands up well in use with foods?
>>----------------------------Original message----------------------------
>>A Janet De Boos recipe for the electric kiln to cone 10
>>
>>50-Soda feldspar
>>7-Ball clay
>>6.5-Calcite
>>6-Talc
>>10.5-Bone ash
>>20-Silica
>>
>>A bright red used extensively here, we call it tomato red, it has a nice
>>glow and responds well to overglazing with ash glazes or high
>>feldspathic glazes.
>To be a bright red it needs 8-10% Fe2O3. This is a variant of the Shiga
>Shigeo Tomato Red a very common glaze in Japan. It is very variable and
>is best with a soak or slow cooling to develop crystals. In this form,
>without the Iron you get a milky glaze that give a bright red responce to
>iron brush work (Especially in reduction) It is a very stable glaze.
Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
Web page: http://digitalfire.com/education/people/ronroy.htm
Leo Smith on sun 15 nov 98
Ron Roy
>----------------------------Original message----------------------------
>This is interesting - when I calculate this glaze for an oxidation firing
>it looks like a durable glaze - even with 10% iron added.
>
>If I include the iron as a flux - read reduction firing - then it is
>seriuosly short of silica.
>
>The question now becomes - how do we know it is a stable glaze when fired
>in reduction with 10% RIO.
Although I haven't used it for years (It was my main research area as a
student in 1975) I did use it (Well one that is very similar) for 15 or
so years and it is very stable even when thick although I used it quite
thinly for the clear version.
>
>If I calculate with 8% RIO the situation looks a bit better but still short
>of silica.
>
>Does anyone know if it stands up well in use with foods?
I still have a mug made in 1978 that is used regularly. It is the version
without the iron and iron brushwork and we still use an iron red bowl
from the research period.
It is redder over light clays, and with the addition of 3% bentonite I
was able to use it a s a raw glaze.
>>>----------------------------Original message----------------------------
>>>A Janet De Boos recipe for the electric kiln to cone 10
>>>
>>>50-Soda feldspar
>>>7-Ball clay
>>>6.5-Calcite
>>>6-Talc
>>>10.5-Bone ash
>>>20-Silica
>>>
>>>A bright red used extensively here, we call it tomato red, it has a nice
>>>glow and responds well to overglazing with ash glazes or high
>>>feldspathic glazes.
>>To be a bright red it needs 8-10% Fe2O3. This is a variant of the Shiga
>>Shigeo Tomato Red a very common glaze in Japan. It is very variable and
>>is best with a soak or slow cooling to develop crystals. In this form,
>>without the Iron you get a milky glaze that give a bright red responce to
>>iron brush work (Especially in reduction) It is a very stable glaze.
Best Wishes
Leo
----------------------------------------------------------------------
Leonard Smith
Rosedale Street Gallery
2A Rosedale Street cnr Old Canterbury Road
Dulwich Hill NSW 2203 Australia
Ph: + 61 2 9518 1182 Fax: + 61 2 9518 1183
Email: leothelion@bigfoot.com
WWW. http://www.bigfoot.com/~leothelion
----------------------------------------------------------------------
Marshall on sun 15 nov 98
it looks ok to me ....70% of my most interesting glazes are outside limit
formular recomendations. after all what does short of silica mean? dry or
satin surface ...slightly less durable...high soda will probably craze...I
am affraid the standards set for industry (if this is what you are refering
to) just don't have much to do with what I do. This glaze, although I
have never used it is probably quit tough as most calcium glazes are. Lets
have a few more iron orange glazes to compare. And slap in a bit of barium
to puch up that colour response and really scare us. p.s. less than 10%
barium is usually safe. the V.C. woo yellow was tested with 9% BaCO3 as I
recall.... Bone Ash and barium is still the way to go I contend!!
>----------------------------Original message----------------------------
>This is interesting - when I calculate this glaze for an oxidation firing
>it looks like a durable glaze - even with 10% iron added.
>
>If I include the iron as a flux - read reduction firing - then it is
>seriuosly short of silica.
>
>The question now becomes - how do we know it is a stable glaze when fired
>in reduction with 10% RIO.
>
>If I calculate with 8% RIO the situation looks a bit better but still short
>of silica.
>
>Does anyone know if it stands up well in use with foods?
>>>----------------------------Original message----------------------------
>>>A Janet De Boos recipe for the electric kiln to cone 10
>>>
>>>50-Soda feldspar
>>>7-Ball clay
>>>6.5-Calcite
>>>6-Talc
>>>10.5-Bone ash
>>>20-Silica
>>>
>>>A bright red used extensively here, we call it tomato red, it has a nice
>>>glow and responds well to overglazing with ash glazes or high
>>>feldspathic glazes.
>>To be a bright red it needs 8-10% Fe2O3. This is a variant of the Shiga
>>Shigeo Tomato Red a very common glaze in Japan. It is very variable and
>>is best with a soak or slow cooling to develop crystals. In this form,
>>without the Iron you get a milky glaze that give a bright red responce to
>>iron brush work (Especially in reduction) It is a very stable glaze.
>
>Ron Roy
>93 Pegasus Trail
>Scarborough, Ontario
>Canada M1G 3N8
>Tel: 416-439-2621
>Fax: 416-438-7849
>
>Web page: http://digitalfire.com/education/people/ronroy.htm
Marshall on wed 18 nov 98
Dear Roy,
I appreciate I was being a bit flippant in my first email and some what
playing devils advocate. I am well aware that it is the glass in a glaze
that creates the durability however it is true to say that small additions
of calcium (a flux present in nearly all 9/10 glazes) does help make a
harder glass..calcium borate glasses being an example of this. Generally
most satin-matt glazes are starved of silica to create the surface
consequently a less durable glaze is inevitable. The sio2;al2o3 ratio of
matt glazes will usual be 5:1 or less. Does this mean we shouldn't use
them? However I always use durable glazes on serving surfaces as I am sure
most potters do.
As for barium, yes what I said isn't true and it certainly has nothing to
do with glaze hardness. However Barium should not release if it is properly
bonded in the glass (BaO 2Sio2). The reason I suggest additions of barium
in iron oranges is because it does help the colour response...but as always
should be used with care. Like wise with Bone ash, used as one of the
sources of calcium the traces of phosphorous seem for some reason to help
the reds and oranges to develop.
I do still hold to the general principle that although durability is always
a consideration, as an artist you have to compromise, if you want certain
colours or surfaces you may end up with a slightly less durable glaze. If I
were to make all my glazes shiny craze free hard glazes I don't think I
would sell any at all. I personally have a satin surfaced iron orange
glazed bowl which I have used for 8 years. A silica starved glaze
surviving that long immpossible...............Yours Will
>----------------------------Original message----------------------------
>Hi Marshall,
>
>If a glaze is short of silica there is the possibility that it will be
>degraded by acidic foods. The more the silica is under the lower limits the
>less durable it will be. So far the examples of glazes discolouring in use
>posted to this list have been short of silica.
>
>I agree that unbalanced glazes often are more interesting - not always -
>for instance the floating blue looks like a durable glaze - my Tenmoku is
>durable.
>
>The amount of Barium or Calcium in a glaze - if within the limits - is not
>the primary consideration for a durable glaze - it's the alumina and silica
>which are the main consideration.
>
>The statement that less than 10% barium is safe is simply not true - what
>determines what leaches out of a glaze depends on the quality of the glass
>- what determines the quality of the glass - more than anything else - is
>the silica content.
>
>Use what ever glazes you prefer - but keep this in mind - if you are making
>functional ware and putting unbalanced glazes where they can come in
>contact with foods - sooner or later you are going to have some explaining
>to do - thats if the customer decides to come back at all. I leave it to
>your imagination - what goes through a persons mind when a glaze loses some
>of its colour after being in contact with some fruit over night?
>
>RR
>
>
>
>
>Ron Roy
>93 Pegasus Trail
>Scarborough, Ontario
>Canada M1G 3N8
>Tel: 416-439-2621
>Fax: 416-438-7849
>
>Web page: http://digitalfire.com/education/people/ronroy.htm
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