Heloisa Nunes on thu 10 nov 05
Hello,
Please, glaze gurus everywhere, have you tested this recipe (I got from a
friend and saw that the archives has many recipes with this name), and
is it food safe at cone 6-7 oxidation? Would it still be food safe if I
increase the Iron Oxide to 5 % and Cobalt to 1 % to get a mat coffee brown?
Tea Dust
Potash feldspar 50
Kaolin 15
Silica 5
Whiting 15
Red iron oxide 0.5
Manganese dioxide 0.5
Cobalt carbonate 0.5
Na2O 0.07 Al2O3 0.42 SiO2 2.33
K2O 0.17 P2O5 0.00
MgO 0.00 TiO2 0.00
CaO 0.46 Fe2O3 0.10
MnO 0.17
CoO 0.13
Alumina:Silica ratio is 1.00:5.50
Neutral:Acid ratio is 1.00:5.73
Alk:Neut:Acid ratio is 1.00:0.42:2.43
Expansion: 85.3 x 10e-7 per degree C
Thank you so much for any input!!!
Heloisa Nunes
Sao Paulo, SP
Brazil
Bruce Girrell on thu 10 nov 05
I don't see how this is a teadust recipe. There is no magnesium to help form
pyroxene and there is way too little iron oxide. Are you sure it's not RIO
5.0 instead of 0.5? Are you sure there's no talc or dolomite in there?
Bruce "but then what do I know?" Girrell
Please, glaze gurus everywhere, have you tested this recipe (I got from a
friend and saw that the archives has many recipes with this name), and
is it food safe at cone 6-7 oxidation? Would it still be food safe if I
increase the Iron Oxide to 5 % and Cobalt to 1 % to get a mat coffee brown?
Tea Dust
Potash feldspar 50
Kaolin 15
Silica 5
Whiting 15
Red iron oxide 0.5
Manganese dioxide 0.5
Cobalt carbonate 0.5
Na2O 0.07 Al2O3 0.42 SiO2 2.33
K2O 0.17 P2O5 0.00
MgO 0.00 TiO2 0.00
CaO 0.46 Fe2O3 0.10
MnO 0.17
CoO 0.13
Alumina:Silica ratio is 1.00:5.50
Neutral:Acid ratio is 1.00:5.73
Alk:Neut:Acid ratio is 1.00:0.42:2.43
Expansion: 85.3 x 10e-7 per degree C
Thank you so much for any input!!!
Heloisa Nunes
Sao Paulo, SP
Brazil
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John Hesselberth on thu 10 nov 05
On Nov 10, 2005, at 8:58 AM, Heloisa Nunes wrote:
> Hello,
>
> Please, glaze gurus everywhere, have you tested this recipe (I got =20
> from a
> friend and saw that the archives has many recipes with this name), and
> is it food safe at cone 6-7 oxidation? Would it still be food safe =20
> if I
> increase the Iron Oxide to 5 % and Cobalt to 1 % to get a mat =20
> coffee brown?
>
Hello Heloisa,
I recalculated your recipe taking the cobalt and manganese out of =20
unity--my usual method. Doing this causes the numbers to shift quite =20
a bit. I also notice that it only adds to 85 without the colorants--=20
have you left something out? As it is, this looks more like a cone =20
10 recipe because it has fairly high levels of silica and alumina and =20=
no boron or zinc--I have pasted my calculations below. I would have =20
to predict that this is an unmelted matte or semimatte and they are =20
not very durable in my experience. The recipe contains low levels of =20
colorants so you may have adequate durability at cone 6-7, but it is =20
not a glaze I would use on functional work. As you increase the =20
colorant levels my concern would increase, although at least iron, =20
cobalt and manganese are relatively easy to keep in a glaze.
Regards,
John
------
Recipe Name: Tea Dust
Cone: 6-7 Color:
Firing: Oxidation Surface:
Amount Ingredient
50 Feldspar--Potash
15 Whiting
15 Kaolin--EPK
5 Silica
85 Total
Additives
.5 Iron Oxide--Red
.5 Cobalt Carbonate
.5 Manganese Dioxide
Unity Oxide
.106 Na2O
.235 K2O
.006 MgO
.653 CaO
1.000 Total
.604 Al2O3
.005 Fe2O3
3.356 SiO2
.002 TiO2
.001 P2O5
5.6 Ratio
79.9 Exp
Comments:
-----------------------------------
Calculations by GlazeMaster=99
www.masteringglazes.com
------------------------------------
Alisa Liskin Clausen on thu 10 nov 05
>
>Please, glaze gurus everywhere, have you tested this recipe (I got from a
>friend and saw that the archives has many recipes with this name), and
>is it food safe at cone 6-7 oxidation? Would it still be food safe if I
>increase the Iron Oxide to 5 % and Cobalt to 1 % to get a mat coffee
brown?
Dear Heloise,
Skipping over the glaze gurus everywhere, I would like to reply!
You have seen many recipes with this name, because it refers to a surface
quality, rather than a recipe with that particular name. When we speak of
tea dust, we speak of iron crystals that look like golden flecks, usually
in an iron rich ground color.
If you alter the recipe to get a mat brown, than that is not a tea dust.
Only a lab test can tell you for sure if the glaze in question is safe for
food.
Let us look at Ian Currie's Teadust Set,
recipe 18
30.62 K Feldspar
12.25 Whiting
12.25 Dolomite
6.12 Spodumene
16.25 Kaloin
22.5 Silica
ADD
10 RIO
If you look at his website, download this as a home recipe, and make the
grid, you find many teadusts and some lovely tenmokus, at a range of
temperatures between Cone 5-9.
If you want a mat brown, you can test a lot of glazes, and about 35% will
be mat brown!
Good luck, hope you are finding your legs again, back in Brazil.
Greetingsto Cibele.
Alisa in Denmark
Ron Roy on mon 14 nov 05
Hi Heloisa,
I will not melt at cone 6 or 7 - it would need some boron or zinc - and the
alumina is way high - one of the criteria for stability depends on a
certain amount of melting.
I will also craze on most clay bodies.
Adding more iron and cobalt will not help the melt in oxidation anyway.
On the other hand - nothing particularly toxic in it but it will change
colour when used under acidic foods.
RR
>Please, glaze gurus everywhere, have you tested this recipe (I got from a
>friend and saw that the archives has many recipes with this name), and
>is it food safe at cone 6-7 oxidation? Would it still be food safe if I
>increase the Iron Oxide to 5 % and Cobalt to 1 % to get a mat coffee brown?
>
>Tea Dust
>Potash feldspar 50
>Kaolin 15
>Silica 5
>Whiting 15
>Red iron oxide 0.5
>Manganese dioxide 0.5
>Cobalt carbonate 0.5
>
>Na2O 0.07 Al2O3 0.42 SiO2 2.33
> K2O 0.17 P2O5 0.00
> MgO 0.00 TiO2 0.00
> CaO 0.46 Fe2O3 0.10
> MnO 0.17
> CoO 0.13
>
>Alumina:Silica ratio is 1.00:5.50
>Neutral:Acid ratio is 1.00:5.73
>Alk:Neut:Acid ratio is 1.00:0.42:2.43
>
>Expansion: 85.3 x 10e-7 per degree C
>
>Thank you so much for any input!!!
>Heloisa Nunes
>Sao Paulo, SP
>Brazil
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
mtigges@NOSPAM.SHAW.CA on mon 14 nov 05
On Mon, Nov 14, 2005 at 01:45:24PM -0500, Ron Roy wrote:
> I will not melt at cone 6 or 7
I already knew that you were special Ron, but that's AMAZING!
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