Sandy Henderson on wed 26 may 04
Dear clayarters,
I "inherited" 25 lbs or so of dry material labeled "black firing clay." It makes a nice
black slip or dark brown slip glaze. It occurred to me that this clay may contain
manganese. Is there any way to tell? Or should I just assume manganese and take
appropriate precautions? Thanks for your help.
Sandy Henderson
in Northwest Indiana
Ron Roy on thu 27 may 04
Hi Sandy,
Yes - assume it has manganese in it - avoid the dust and fumes.
RR
>Dear clayarters,
>
>I "inherited" 25 lbs or so of dry material labeled "black firing clay."
>It makes a nice
>black slip or dark brown slip glaze. It occurred to me that this clay may
>contain
>manganese. Is there any way to tell? Or should I just assume manganese
>and take
>appropriate precautions? Thanks for your help.
>
>Sandy Henderson
>in Northwest Indiana
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on fri 28 may 04
Dear Sandy Henderson,
One way to find out what the colouring compounds are in a clay is do a
"Borax Bead Test" This requires having a quantity of Sodium Tetra
Borate, aka Borax and a Platinum wire. But at $US 900 per Troy oz a
couple of inches will cost you a few dollars. Fresh bright Nichrome
wire can be substituted.
Instructions can be found in some elementary College Chemistry Books.
The colours to look for from Manganese are Red Violet in a reducing
flame and colourless in an oxidising flame.
But Beware, if there are other elements such as Iron, Chromium,
Nickel, Copper or Cobalt in the clay it would be necessary to do a
chemical separation.
If you know the wavelengths, and there are tables of these to be had,
then a spectrometer is the way to go. OK of colleges and universities
but out of range of we common potters.
Best regards,
Ivor Lewis. Redhill, South Australia
Potters Council Member
.
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