Michael Banks on thu 4 may 00
Ann,
Yellow chrome oxide is not common in nature, in fact the only yellow chrome
mineral I know of is the rare mineral tarapacaite (K2 CrO4) which occurs in
evaporite salt deposits in Chile. Crocoite (lead chromate) fuses easily in
glaze to a strong green, but is usually bright red or orange in colour.
Chromite (iron chromium oxide) is black and highly refractory.
Your pebble is much more likely to be a vanadium, uranium, lead or
molybdenum complex oxide. Some candidates could include autinite (calcium
uranate phosphate), carnotite (potassium uranate vanadate), or wulfenite
(lead molybdate). These minerals all have bright yellow earthy forms and
are capable of greens in glazes.
Michael
in New Zealand
Ann Brink wrote:
> I've never heard of this before but your question may tie in with
something
> I've been meaning to ask the group about. A few years ago, I picked up a
> few pebbles in western New Mexico because the color was similar to yellow
> ochre. When I got home I pulverized one of the pebbles- it was fairly
soft-
> and mixed a little of the powder into some clear glaze and tried it on
test
> tiles. I was amazed to see grass green spots the next day! Not a copper
> green at all, but clear green, with a hint of yellow. This was cone 7
> oxidation by the way (snip)
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