John Rodgers on sat 18 sep 10
I have some glazes that are supposed to be green, but are brown. They
call for Chrome Oxide - which is very green in appearance as a prepared
oxide - and Cobalt Oxid - near black in appearance. but when together in
a fired glaze make for brown. Would not Copper oxide or Copper Carbonate
with the Cobalt make a green? I could test - but hope someone has been
through this already.
Thanks
--
John Rodgers
Clayartist and Moldmaker
88'GL VW Bus Driver
Chelsea, AL
Http://www.moldhaus.com
Robert Harris on sun 19 sep 10
Hi John,
I've used cobalt and chrome together to make nice greeny blues (and
bluey greens). I would suggest that it goes brown for a different
reason. The first one that pops to mind is that Zinc turns Chrome a
nasty brown. From what I remember of your posts you fire in reduction,
so I assume you don't have zinc in your recipes anyway...
I fire cone 10 electric so maybe it is a reduction thing also (theory
tells me this is unlikely)?
Anyway, I'm pretty sure it's not the Chrome and Cobalt together that
is a problem per se, but something about your base. Without seeing the
recipe I can't offer any other suggestions.
Hope this helps in some way.
Robert
On Sat, Sep 18, 2010 at 11:06 PM, John Rodgers wrote:
> =3DA0I have some glazes that are supposed to be green, but are brown. The=
y
> call for Chrome Oxide - which is very green in appearance as a prepared
> oxide - and Cobalt Oxid - near black in appearance. but when together in
> a fired glaze make for brown. Would not Copper oxide or Copper Carbonate
> with the Cobalt make a green? I could test - but hope someone has been
> through this already.
>
> Thanks
>
> --
> John Rodgers
> Clayartist and Moldmaker
> 88'GL VW Bus Driver
> Chelsea, AL
> Http://www.moldhaus.com
>
--=3D20
----------------------------------------------------------
Eric Hansen on sun 19 sep 10
Iron, chrome, & copper all produce greens. Typical example of iron
green is green cealdon. chrome, like iron produces many colors,
depending on formulation as well as firing techniques. Copper gets,
well all the colors you see on oxidized pennies, such as white,
greens, reds, blacks, browns, as well as metallic copper.
- h a n s e n
On Sat, Sep 18, 2010 at 11:06 PM, John Rodgers wrote:
> =3DA0I have some glazes that are supposed to be green, but are brown. The=
y
> call for Chrome Oxide - which is very green in appearance as a prepared
> oxide - and Cobalt Oxid - near black in appearance. but when together in
> a fired glaze make for brown. Would not Copper oxide or Copper Carbonate
> with the Cobalt make a green? I could test - but hope someone has been
> through this already.
>
> Thanks
>
> --
> John Rodgers
> Clayartist and Moldmaker
> 88'GL VW Bus Driver
> Chelsea, AL
> Http://www.moldhaus.com
>
--=3D20
Eric Alan Hansen
Stonehouse Studio Pottery
Alexandria, Virginia
americanpotter.blogspot.com
thesuddenschool.blogspot.com
hansencookbook.blogspot.com
"To me, human life in all its forms, individual and aggregate, is a
perpetual wonder: the flora of the earth and sea is full of beauty and
of mystery which seeks science to understand; the fauna of land and
ocean is not less wonderful; the world which holds them both, and the
great universe that folds it in on everyside, are still more
wonderful, complex, and attractive to the contemplating mind." -
Theodore Parker, minister, transcendentalist, abolitionist (1810-1860)
KATHI LESUEUR on sun 19 sep 10
On Sep 18, 2010, at 11:06 PM, John Rodgers wrote:
> I have some glazes that are supposed to be green, but are brown. They
> call for Chrome Oxide - which is very green in appearance as a =3D
prepared
> oxide - and Cobalt Oxid - near black in appearance. but when together =3D
in
> a fired glaze make for brown. Would not Copper oxide or Copper =3D
Carbonate
> with the Cobalt make a green? I could test - but hope someone has been
> through this already.
>=3D20
> Thanks
>=3D20
> --
> John Rodgers
> Clayartist and Moldmaker
> 88'GL VW Bus Driver
> Chelsea, AL
> Http://www.moldhaus.com
The green on the pots on my website uses 1 percent chrome oxide. I have =3D
a variation of it that uses 1% chrome and .25% cobalt carbonate. The =3D
cobalt gives it a slightly bluish tint. If you use too much chrome or =3D
don't apply the glaze thickly enough you will get a brown. My =3D
understanding is that chrome is unaffected by reduction.
KATHI LESUEUR
http://www.lesueurclaywork.com
>=3D20
William & Susan Schran User on sun 19 sep 10
On 9/19/10 2:16 PM, "Robert Harris" wrote:
> I've used cobalt and chrome together to make nice greeny blues (and
> bluey greens). I would suggest that it goes brown for a different
> reason. The first one that pops to mind is that Zinc turns Chrome a
> nasty brown. From what I remember of your posts you fire in reduction,
> so I assume you don't have zinc in your recipes anyway...
To John and all,
My other post I had written that chrome & tin make brown - MISTAKE!!
As Robert points out, it is zinc and chrome that form brown, even if you
just have a little zinc in the glaze.
My apologies. I had just written an answer to one of my students about
materials and colors in glazes and simply had a brain fart - the silent
deadly kind...
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
William & Susan Schran User on sun 19 sep 10
On 9/18/10 11:06 PM, "John Rodgers" wrote:
> I have some glazes that are supposed to be green, but are brown. They
> call for Chrome Oxide - which is very green in appearance as a prepared
> oxide - and Cobalt Oxid - near black in appearance. but when together in
> a fired glaze make for brown. Would not Copper oxide or Copper Carbonate
> with the Cobalt make a green? I could test - but hope someone has been
> through this already.
Hey John,
Does the glaze have tin in it?
Chrome & tin can make red color in some instances, but can also make brown.
If it has tin oxide, remove it and substitute zircopax, superpax or
zirconium silicate, but may need to double amount of opacifier.
Bill
--
William "Bill" Schran
wschran@cox.net
wschran@nvcc.edu
http://www.creativecreekartisans.com
Michael McDowell on mon 20 sep 10
John Rodgers mentions that he is trying to get a green color from additions
of chrome and cobalt, and is instead getting brown.
John, there are a few different scenarios that would contribute to this
problem. If you are doing a "body reduction" early in the fire and getting
good results from celedon and copper red recipes, then I would suggest that
the early reduction is in fact driving off the chrome as a vapor. That stil=
l
does not account for brown, rather than cobalt blue as an outcome. This
leads to the suspicion that the chrome may be a green powder other than pur=
e
chrome oxide. Then whatever was left in that green powder could nudge the
blue to a brown. Chrome oxide itself is a strong green colorant, though it
can be "harsh" which is why it is often muted with some other oxides. My
suggestion here would be to test your glaze in a few different firing
regimes such as straight oxidation, or starting reduction only after bisque
temp.
Exploring further the possibilities of chemical mislabeling. What about thi=
s
black powder that you are using as cobalt? Will it produce a strong blue by
itself? There are lots of black powders your ceramic supplier could mislabe=
l
or you.
Copper oxide or carbonate can produce a good deep green with additions of 4=
%
or more. But I don't see why the cobalt would be necessary. I'm not sure
they play together well. Copper has a number of it's own problems. It will
be sensitive to atmosphere so that differences in timing and degree of
reduction will alter the shade of green. I've found that the chemistry of
the glaze will also affect the shade of green. High calcium glazes seem to
display green from copper nicely, attempting to substitute magnesium for
some of the calcium to reduce COE (and crazing) does not help the green.
There is also some concern that copper seems to "soften" glazes so that the=
y
leach into food acids more readily.
Michael McDowell
Whatcom County, WA, USA
michael@mcdowellpottery.com
http://www.McDowellPottery.com
Bonnie Staffel on mon 20 sep 10
< I have some glazes that are supposed to be green, but are brown. They
call for Chrome Oxide - which is very green in appearance as a prepared
oxide - and Cobalt Oxide - near black in appearance. but when together =3D
in
a fired glaze make for brown. Would not Copper oxide or Copper Carbonate
with the Cobalt make a green? I could test - but hope someone has been
through this already.>
I make a beautiful green glaze using cobalt in Albany Slip. The iron =3D
alters
the blue of the cobalt to make green. I have been using this combination =
=3D
for
years on top of a white glaze.
Bonnie Staffel
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD=3DA0 Throwing with Coils and Slabs
DVD=3DA0 Introduction to Wheel Work
Charter Member Potters Council
Paul Haigh on tue 21 sep 10
I have mixed cobalt with a rutile/iron glaze and came up with green. It was=
, on occasion spectacular and sometimes... ehhh. This is in part because I =
didn't really control the concentrations and because I'm firing in wood so =
there were lots of variables that I didn't explore.
Paul Haigh
Wiley Hill Mudworks
Web: http://wileyhill.com
Facebook: http://tinyurl.com/28ggv3w
etsy: http://www.etsy.com/shop/WileyHillMudworks
Neon-Cat on tue 21 sep 10
If you just had to have that special army-green color at low temp.
(cone 04 or so) you could use corrosive, orangish-red potassium
dichromate (K2Cr2O7) in a base glaze (1 tsp/1 cup glaze). Be careful,
though -- it can be absorbed through the skin.
Marian
neoncat
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