Does anyone know what causes the blue color in blue Chalcedony? I’m
especially interested in colorant of the darker blue material from
Namibia.
Derek Levin
www.gemmaker.com
Does anyone know what causes the blue color in blue Chalcedony? I'm especially interested in colorant of the darker blue material from Namibia.
Natural blue color in Chalcedony is due to Tindal effect, which is
the same phenomena which makes our sky blue. Ray of light scatter on
their way through a medium and that gives off blue coloration.
However, if you observing darker shades of blue then the cause
probably is artificial treatment. Standard practice for coloring
Chalcedony blue is impregnation with potassium ferrocyanide
(prussian yellow) and with subsequent boiling in solution of
sulfate pentahydrate (blue vitriol of copper).
Leonid Surpin
I have cut numerous pieces of the Namibian blue chalcedony, and had
the same question. One clue is that its color by transmitted light
tends toward a pale brownish orange, indicating that scattering of
blue wavelengths is occurring. This is the same phenomenon that
causes a blue sky, or the bluish tinge of water with a little milk
in it. Whether the scattering is caused by minute particles or voids
or some other type of inclusion is to be determined (or perhaps
already has been) by a well-equipped investigator. Some pieces a
lighter, some tend toward more purplish shades, so the size of the
particles causing the scattering must vary slightly, or perhaps there
is a mix of particle sizes.
Perhaps someone out there has more to offer on this subject.
Dick D.