Bacia Edelman on mon 14 sep 98
Carol Young: Here is one to try, and it comes from Lana Wilson's book
"Ceramics: Shape and Surface"
cone 6 oxidation
Heino-Render Satin Matt ( a food safe functional glaze at cone 6)
Potash Feldspar 30.
Neph. Syenite 20.
Whiting 17.
Gerstley borate 4.
Zinc Oxide 9.
Kaolin 14.
Silica 5.
Bentonite 2.
Add 4 % Rutile.
..
To get the flecks in it that you desire, you might try a black slip or an
iron oxide slip underneath
This glaze can produce pinholes if bisque is too low-fired or application is
thick. Smooth out any visible pinholes after glazing.
Lana also suggests adding mason stains to a slip for 1st coat, or painting
designs on top of glaze with iron oxide and cobalt carbonate.
Other colors are suggested by Render who adapted this glaze (in Lana's
class) from Heinos. A mottled gray tan, e.g. has 1 % nickel ox.
Worth testing and let us know if you do, what luck you have.
Bacia Edelman Madison, WI
John Post on tue 15 sep 98
>----------------------------Original message----------------------------
> Carol Young: Here is one to try, and it comes from Lana Wilson's book
>"Ceramics: Shape and Surface"
>cone 6 oxidation
>
>Heino-Render Satin Matt ( a food safe functional glaze at cone 6)
>
>Potash Feldspar 30.
>Neph. Syenite 20.
>Whiting 17.
>Gerstley borate 4.
>Zinc Oxide 9.
>Kaolin 14.
>Silica 5.
>Bentonite 2.
>Add 4 % Rutile.
>.
I haven't followed all of this thread, but if the goal here is to get a
good food safe functional glaze then this one won't work. The Lana Wilson
approach to glaze making is on the material level. In her book she
describes how to create new glazes by combining different materials
together. She doesn't look at the glaze from a molecular viewpoint. Her
methods do work if your goal is to create visually interesting non-foodsafe
glazes.
BUT if you are trying to create a durable glaze this method is not enough.
*A foodsafe glaze at cone 6 should have between 2.5 and 3.5 moles of
silica. This glaze falls short of that range since its SiO2 amount is 1.92.
===========================
Chemical Analysis
===========================
Na2O 0.13 Al2O3 0.39 SiO2 1.92
K2O 0.11 B2O3 0.04 TiO2 0.11
MgO 0.01 Fe2O3 0.01
CaO 0.47
ZnO 0.28
Alumina:Silica ratio is 1.00 : 4.95
Neutral:Acid ratio is 1.00 : 4.75
Alkali:Neutral:Acid ratio is 1.00 : 0.43 : 2.04
Is this is a good glaze? Certainly, it looks great. I use it on my pots,
but I don't use it on surfaces that come into contact with food.
On the plus side for this glaze is that it looks nice and the recipe was
posted here to clayart with the cone, atmosphere and an information about
its origin.
As for an easy way to get speckles...
I recently moved a couple of metal file cabinets in the studio. The
bottoms were quite rusty. I scooped up all of the rust that fell off the
bottom of the cabinets, ran it through a 60 mesh sieve and added it to a
fat white glaze. I fired the glaze to cone 6 in my electric kiln and the
result was a nice white glaze with brown iron flecks similar to the iron
spots that might occur during a reduction firing. You might try this with
a glaze that already works well for you.
Cheers,
John Post
rp1mrvl@moa.net
Sterling Heights, MI USA
Ron Roy on fri 18 sep 98
I am interested to know why this is thought to be food safe? I have
compared it to two sets of limit formulas and it shows up short of silica
in both cases.
I realize there are no serious toxins present - but it appears to be less
than durable.
I would think it would leach and/or change colour under certain conditions.
>----------------------------Original message----------------------------
Here is one to try, and it comes from Lana Wilson's book
>"Ceramics: Shape and Surface"
>cone 6 oxidation
>
>Heino-Render Satin Matt ( a food safe functional glaze at cone 6)
>
>Potash Feldspar 30.
>Neph. Syenite 20.
>Whiting 17.
>Gerstley borate 4.
>Zinc Oxide 9.
>Kaolin 14.
>Silica 5.
>Bentonite 2.
>Add 4 % Rutile.
>.
>To get the flecks in it that you desire, you might try a black slip or an
>iron oxide slip underneath
>
>This glaze can produce pinholes if bisque is too low-fired or application is
>thick. Smooth out any visible pinholes after glazing.
>Lana also suggests adding mason stains to a slip for 1st coat, or painting
>designs on top of glaze with iron oxide and cobalt carbonate.
>Other colors are suggested by Render who adapted this glaze (in Lana's
>class) from Heinos. A mottled gray tan, e.g. has 1 % nickel ox.
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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