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glossy black/cone 6 ox/safety or not?

updated wed 24 feb 99


Maridel Crawford-Brown on tue 23 feb 99

Hello again list;
I have been using the following glossy black cone 6 ox which has a
consistently high gloss and even finish, and if definitely black, but have
become concerned as to whether or not it is food safe, and also concerned
about the method of mixing it. Is this dry sieving needed? It can raise
quite a bit of dust depending.... I would prefer to find a glossy black
without nickel oxide and, maybe also without manganese.

Glossy Black, Cone 6 ox
mix the following as a stain, sieving through a coarse screen while dry:
cobalt carb 31
green chrome oxide 7
black iron oxide 37
manganese dioxide 12
nickel oxide 13

Add 70 g of the above to 1000g of the following clear gloss:
Frit 3134 500
Kaolin 300
silica 200

The reason I am concerned about food safety with the above glaze is a black
glossy was in use, which was later said not to be food safe, and which was
as follows:
custer feldspar 4 parts
whiting 4 parts
flint 3parts
kaolin 3 parts
GB 2parts
(measured dry as say, I cup, 3/4 cup, 1/2 cup)
cobalt oxide 2% of dry weight
chrome oxide 2% of dry weight
black iron oxide 2% dry weight
Copper oxide 2% dry weight

Comments on this one appreciated, as I struggle to understand glazes,etc.