Lesley Alexander on mon 18 feb 02
Does anyone know why zinc turns chrome brown? Lesley
ADAM JARZEMBOWSKI on mon 18 feb 02
>From: Lesley Alexander
>Reply-To: Ceramic Arts Discussion List
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Zinc and chrome
>Date: Mon, 18 Feb 2002 02:00:52 -0800
>
>Does anyone know why zinc turns chrome brown? Lesley
>
It is very common for zinc to cause discolouration in glazes. With soda,
potash, and calcia, the zinc oxide gives clean colours with cobalt and and
copper oxides. With other colouring oxides gives mottled effects which are
dull with muddy opacity. Even a small amount of zinc oxide in a glaze will
upset many colors used as stains or underglazes.
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Fara Shimbo on tue 19 feb 02
Hi, Leslie,
I *think* zinc turns chrome brown due to the formation
of zinc chromates or zinc-chrome spinels. But then again,
it doesn't always turn zinc brown. In most of my
crystalline glaze formulae, chrome gives an apple green
ground with golden crystals, when used in amounts up
to 1%. Any higher and I get this grass-green, blistering
awfulness; but I almost never get a brown ground.
Fa
--
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Fara Shimbo, Certified Public Nuisance, Master Crystallier
Route 66 Ceramics, Hygiene, Colorado, USA
crystalline-ceramics.info ++ crystalglazes.info
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
"It's great to be known. It's even better to be known
as 'strange.'" -- Kaga Takeshi
iandol on wed 20 feb 02
Dear Lesley Alexander=20
You ask <>
Quite simple. There is a chemical reaction between zinc oxide and chrome =
oxide which results in a new chemical, brown in colour, called Zinc =
Chromite. There are extensive records detailing the investigation of =
this phenomena going back to about 1910. Note that the varied chemistry =
of chrome brings a lot of coloured chemicals into existence. Some of =
these are yellow, others orange beside the green we are familiar with =
which is stable in reduction. Oxidising conditions seem to favour their =
formation. Reduction as we have read in Clayart tends to remove Zinc =
from the glaze.
Best regards,
Ivor.
Best regards,
Ivor Lewis
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