John Weber on thu 10 jul 97
Help! Does anyone know of a base glaze for Cone 6 Oxidation, that will meet
the requirments of Degusse Red Stain. The manufacturer states the base glaze
must be one which cannot contain any Feldspars, Lithium, Sodium, Potassium,
or Magnesium and if it has Zinc it needs to be less than 5% and Calcium
cannot exceed 20%. I want a glaze that is satin or semi matt. These
criteria just about exhaust my glaze list. If anyone knows of a glaze that
meets this criteria I would sincerely appriciate it. Thanks.
Karl P. Platt on fri 11 jul 97
> The manufacturer states the base glaze
> must be one which cannot contain any Feldspars, Lithium, Sodium, Potassium,
> or Magnesium and if it has Zinc it needs to be less than 5% and Calcium
> cannot exceed 20%.
I'm looking at US Patent 5.389.402: "Method for producing decorations
which are color stable in a porcelain firing and a pigment composition
suitable therefor."
What is this? It's THE patent for Degussa/Cerdec encapsulated stains.
I don't know what you're reading there, but it conflicts with the patent
literature -- and my experience.
ZnO in the glaze would serve to stabilize the pigment. Likewise, a
little cerium oxide would be of benefit. Zn has an affinity for S and
Se. This serves to prevent them from evaporating out of the glaze. The
cerium acts to ensure oxidizing conditions inside the glaze melt.
They also lay claim to 50 wt% ZnO host glasses (frits) for these
pigments. This is probably, more or less, a ZnSiO3 melt (with suitable
minor additions).
You shouldn't have any real problem with any decent cone 6 transparent
glaze. If you use frit, avoid a runny frit - it'll be more prone to
attack (corrode) the pigment. Do add in a few % ZnO for reasons stated
above. The use of cerium may be useful and if you have some around, why
not give it a go. These pigments are not stable in reduction.
I personally feel that they're real mushy colors -- they do not have the
sharply defined colors of CdSSe in a pure form as they are encapsulated
in a "trans[arent" shell of ZrO2. As such any light incident on the
pigment traverses the "capsule" first, where it suffers scattering and
reflection, then it hits the interface of the capsule and pigment, where
it is scattered again and so on as it leaves the pigment to get to your
eye.
There's a way to use these colors to Cone 6 quite apart from the Degussa
system. However, these methods are not something I'm willing to toss out
into the public domain. These involve specially formulated frits, too,
but the pigment is not encapsulated.
--
Heisenberg may have been here.......
Barbara Lewis on fri 11 jul 97
John - I have used the following glaze with the Degussa stains and have
achieved good results. The glaze appeared in an article written by Gerald
Rowan in the December, 1981 issue of CM. It would be worth getting a copy
of the article because there are many color variations suggested, many of
which we've tested and had beautiful results. If you have trouble finding a
copy, e-mail me directly with your address and I'll mail you one. With 5%
tin it is a beautiful, fat white semi-mat glaze. The clay body you use
makes a huge difference. When I have used the glaze over the GWU clay body
(which fires from cones 6-10), the glaze is yucky and transparent. When
used over a cone 6 temp clay made with Redart, it is beautiful.
Base Glaze:
20% Frit 3124
20% Dolomite
20% Spodumene
20% Ball Clay (used OM4)
20% Silica
Note: the original article calls for Frit 3134. After having experimented
with both 3124 and 3134, we found we liked 3124 better. Good luck. Barbara
At 09:27 AM 7/10/97 EDT, you wrote:
>----------------------------Original message----------------------------
>Help! Does anyone know of a base glaze for Cone 6 Oxidation, that will meet
>the requirments of Degusse Red Stain. The manufacturer states the base glaze
>must be one which cannot contain any Feldspars, Lithium, Sodium, Potassium,
>or Magnesium and if it has Zinc it needs to be less than 5% and Calcium
>cannot exceed 20%. I want a glaze that is satin or semi matt. These
>criteria just about exhaust my glaze list. If anyone knows of a glaze that
>meets this criteria I would sincerely appriciate it. Thanks.
>
Karen Gringhuis on sun 13 jul 97
John - Something is wrong with this picture. What you say the
mfgr. says makes NO SENSE. I have used or tested Degussa incl.
pigments in many different bases with no such restrictions.
The only material on your forbidden list I probably missed is
Zinc.
My advice is ignore these restrictions (unless someone else here
has reasons otherwise) & just test the red in some bases you like.
As always - the definition of what WORKS is highly personal,
idiosyncratic & fun. So go have some. Karen Gringhuis
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