The initial correspondent re ‘blue chalcedony’ if I remember
correctly said that the blue stones had come from Germany a long
time ago.
When in the jewellery trade many years ago I remember chalcedony
(agate) from Germany cut and polished into heart shapes for
pendants. These items came in green, blue and carnelian colours.
These were not natural colours and had been introduced into the
stone. I did have the formula for creating these colours at one
time but cannot now remember all the details.
This material was I believe produced in Idar Oberstein in Germany
where all forms of gem cutting were a major business.
It would seem likely that the colour being artificially introduced
to the stones, there is a possibility of varying degrees of fade or
deterioration over long periods of time and given differing
environmental conditions.
Regards, Keith Torckler, Cornwallis, New Zealand