Jeff Gieringer on sun 20 jan 08
Hello to all and I hope 2008 is off to a good start. I have 2 - 3 ^6 Black
glaze reipes that I have used for some time. I just found out this week
that none of them will stay black when used with white. They all turn
some shade of blue. It would be GREATLY appreciated if anyone has a true
black glaze recipe that will stay black when used over white. Thank you
for any help.
Jeff
Ron Roy on mon 21 jan 08
Hi Jeff,
It's the cobalt oxide that is the problem.
You can use iron and manganese but be aware that Manganese is toxic and
avoid the dust and fumes.
RR
>Hello to all and I hope 2008 is off to a good start. I have 2 - 3 ^6 Black
>glaze reipes that I have used for some time. I just found out this week
>that none of them will stay black when used with white. They all turn
>some shade of blue. It would be GREATLY appreciated if anyone has a true
>black glaze recipe that will stay black when used over white. Thank you
>for any help.
>
>Jeff
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ivor and Olive Lewis on tue 22 jan 08
I have posted information in the past about the creation of Black Glazes =
but it may be to scientific.
Technically, Black is due to the absence of light reflected from the =
surface of the glaze. This can be achieved by using mixtures of oxides =
so that the whole of the visible spectrum is adsorbed.
Cobalt oxide in a silicate solution adsorbs all light wavelengths except =
some in the blue end of the spectrum.
Iron oxide that is fired in oxidation is a red orange hue. This adsorbs =
light from the violet blue green side of the colour wheel but reflects =
orange red.
Blue and orange are complementary colours. This can be tested by making =
a dense mixture of Ultramarine and Burnt Sienna artists paints. The =
trick it to get the balance right.
I think a good stain for a black glaze would contain oxides of Cobalt, =
Iron, Manganese, If the glaze is to be fired in a reducing atmosphere =
Copper, Nickel and Chromium would useful.
If people are getting segregation at some time or other with Cobalt =
oxide then they might consider processing their colouring agents. =
Chappell gives instructions. He comments about the fineness of milling a =
calcined batch to get optimum fineness.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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