Ivor and Olive Lewis on wed 8 feb 06
For some time I have been searching for a stable compound of Copper that =
seemed to have potential as a glaze pigment. Most of the natural Copper =
Silicate materials are hydrates and decompose to Black Copper Oxide when =
heated. Copper oxides is soluble in acids, forming Copper Acetate with =
Vinegar. The following information seems to show promise and deserves =
Egyptian blue ("frit," "Pompeiian blue"):
Origin and History: Very stable synthetical pigment of varying blue =
colour. It is one of the oldest man-made colors commonly found on wall =
paintings in Egypt, Mesopotamia and Rome. Many specimens, well over 3000 =
years old, appear to be little changed by the time.=20
Making the Pigment: Heating a mixture of a calcium compound (carbonate, =
sulfate or hydroxide), copper compound (oxide or malachite) and quartz =
or silica gel in proportions that correspond to a ratio of 4 SiO2 : 1 =
CaO : 1 CuO to a temperature of 900=B0C using a flux of sodium =
carbonate, potassium carbonate or borax. The mixture is then maintained =
at a temperature of 800=B0C for a period ranging from 10 to 100 hours.
Chemical Properties: Calcium copper silicate, CaCuSi4O10. It is =
insoluble in acids even in warm temperatures.
Artistic Notes: It has a discreet covering power. It can be used in =
fresco. Not advised in tempera, oil and encaustic.
Note the comment on stability. Insoluble in Acids ! !
Someone with a glaze calculator might like to put forward a series of =
recipes to match the Seger Formula: 4 SiO2 : 1 CaO : 1 CuO. =
Wollastonite might be considered as a potential ingredient
I would like to know if this would remain stable up to cone 10 and would =
like to test any recipes which I can accomplish with ingredients to =
Hope someone will join me in this one.
John Hesselberth on wed 8 feb 06
On Feb 7, 2006, at 7:21 PM, Ivor and Olive Lewis wrote:
> Someone with a glaze calculator might like to put forward a series =20
> of recipes to match the Seger Formula: 4 SiO2 : 1 CaO : 1 CuO. =20
> Wollastonite might be considered as a potential ingredient
Using wollastonite and silica the appropriate wt%s to give a 4/1 mole =20=
ratio of SiO2 to CaO are shown below. There would be very little of =20
anything else in that mix so you could source your fluxes, as you =20
suggest, from sodium/ potassium carbonates and borax to your hearts =20
content. I would start with an amount that might approximate an =20
earthenware glaze composition and increase as needed to get a decent =20
melt. The second recipe below shows a possible starting point using =20
borax and soda ash.
How much copper to add depends on the specific form you choose to =20
use. I'm sure you are aware that what we potters call copper =20
carbonate is usually relatively pure CuC03.Cu(OH)2 -- often called =20
basic copper carbonate. But you could also choose to use one of the =20
copper oxides. I'll let you do that math depending on what you have =20
available and its purity.
Recipe Name: Copper Stain Experiment 1
Recipe Name: Copper Stain Experiment 2
8.2 Soda Ash
Calculations by GlazeMaster=99
Ivor and Olive Lewis on thu 9 feb 06
Dear John Hesselberth,
How much Copper is there in each of your recipes?
Using Copper Oxide (black). Wollastonite and Silica and a bit of mental =
arithmetic I came up with the following to which I would add 10% =
Anhydrous Sodium Carbonate=20
Copper Oxide (CuO) 21.28%
Sodium Carbonate 10.00%
These seem to be good "Ball Park" values to me
Thanks for coming to the party.
John Hesselberth on thu 9 feb 06
On Feb 9, 2006, at 2:04 AM, Ivor and Olive Lewis wrote:
> How much Copper is there in each of your recipes?
I always test with 5% copper carbonate and 6% rutile. No good reason
for the rutile except that is does aid stability and that is what I
built up a large amount of my own data on. So I always test in that
standardized way. Ron and I have recommended using a maximum of 5%
copper carb--and preferably a max of 4%--for several years now. Even
in the best of glazes copper leaching really goes through the roof
when you get up to 6 and 7%.