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Sugar/acid treatment


It was alluded that a like process is used for coloring onyx.
If memory serves, I’ve heard of some complicated sugar process
being used for carnelian, as well. It must be different, yes?
You wouldn’t want to drive carbon into carnelian, so what’s
making it more orange? (This has been a fascinating exchange, by
the way. Thanks for having it.) -Dana Carlson

You wouldn't want to drive carbon into carnelian, so what's >  
  making it more orange?  (This has been a fascinating
exchange, by the way.  Thanks for having it.) - 

Let’s start at the beginning. Agate is a semi-amorphous deposit
of silicon hydroxide, closely similar to silica gel. So agate is
really without much in the way of colour, except that the silica
solutions under high pressure and temperature deep underground
are very likely to dissolve up almost any other minerals going
spare. Thus, the bright apple green variety called chrysoprase
has been coloured with the salts of nickel; blue lace agate is
coloured with cobalt, opaque reds and yellows the result of
mercury oxide and sulphide contamination. And what material is
very common in the ground? Iron, of course. The silicon hydroxide
picks up iron, manganese, all sorts. It doesn’t need much to
colour agate, so a very dilute solution of an iron salt would
rapidly oxidise to the ferric state; ferric oxide or ferric
hydroxide. Thus, prettily laid down bands of browns, oranges,
almost yellows. So there is no shortage of carnelian agate;
every rock shop has plenty for sale cheaply. So why would anyone
want to bother forcing iron compounds into the cryptocrystalline
agates just to simulate carnelian? I have turned agates blue and
blue-green, using ferrous sulphate followed by potassium
ferrocyanide (you get Prussian blue) just as an experiment and I
see plenty of agates in the shops garish shades of violet, green,
scarlet… These are unusual so people take the trouble to dye
the suitable agates. But not carnelian, and you wouldn’t do it
with sugar/acid treatment either, though people do simulate onyx
that way. I’m not sure, but I believe true onyx could be
coloured with manganese black (MnO2) Sorry - I come all over
academic on occasion. It’s a disease I caught in a university.
And Dana - you did say you were interested! But cheers. PS: there
has always been talk about a universal solvent that would
dissolve anything - and they query, 'what would you keep it in?'
Water IS the universal solvent - apply enough pressure and get
it far above it’s atmospheric boiling point - yes LIQUID water at
350C! And that dissolves everything - including gold. Cheers
again. – /\ / / John Burgess, / / / //\ @John_Burgess2 / /
\ / (___) \ (_________)