Tanzanite cant take heat or sudden temperature change so no
ultrasonic, strong sunlight, etc. Oh, and no hydrochloric or
hydrofluoric acid.. whatever that is. So dont leave it on an
expired car battery after..
It’s not even that tanzanite can’t take heat. After all, it owes
it’s purple color to having been heat treated. As you say, what it
cannot tolerate is sudden temperature change. Ultrasonics are a no-no
because tanzanite sometimes is under considerable internal strain due
perhaps to the heat treatment it got. Some of them will shatter in an
ultrasonic. Now, I’ve cleaned a lot of smaller less expensive ones
with both ultrasonics and steam cleaners, but I’ve also broken one or
two over the years (also cheap ones) with the ultrasonic, so don’t
use that on anything you’d mind replacing or a larger higher quality
stone.
Car batteries use sulphuric acid, similar to what used to be used in
pickle pots (and sometimes still is) before most people switched to
sulphuric acid salts. The salts (sodium bisulphate, such as Sparex or
similar) are just as corrosive to those things they affect, including
some stones, but are safer in terms of fumes and ability to burn
skin. I’ve not seen tanzanites be damaged by normal immersion in
pickle, which can be considered dilute sulphuric acid, but I wouldn’t
leave it in there long periods. Hydrochloric, you’re not likely to
be using. And Hydrofluoric you most certainly should NOT be using
unless you’re well equipped to handle this very dangerous acid.
By the way. For those who wonder whether tanzanite is indeed
sensative to sunlight, despite what most here on the list have said,
consider what the damage ultraviolet light (sunlight’s most damaging
part) does. It conveys enough energy to a stone’s atomic structure as
to allow some change, such as knocking an electron out of one orbit
to another different energy one, or otherwise doing something that
affects light absorbtion. It can be compared to annealing in a sense.
Those stones that are sensative to ultraviolet light are generally
also sensative to heat, which is also energy. The amounts of heat
(infrared) needed to make a change might differ from the amounts of
ultraviolet, but you can be fairly certain that a stone like
tanzanite that owes it’s current color to a prior significant heat
treatment, won’t then care about a bit of ultraviolet, since it’s
unlikely that the energy input to the stone from sunlight could
exceed what went into it from heat treating. If it was heated and
then irradiated, well, then this no longer applies.
In general, stones sensative to fading in sunlight are stones that
have NOT been heat treated as the most recent treatment. They often
are either stones that have never been treated at all, and normally
are not exposed to sunlight or high energy during formation, or are
stones which owe some portion of their current color to either
natural or artificial radiation. Treating stones with irradiation
generally affects the color often by doing the exact opposite of
what lower energy ultraviolet can do, that is it induces some damage
to the atomic structure, or knocks some electron to a higher energy
orbit where it remains trapped until something coaxes it back down.
Some early forms of irradiated blue topaz would fade in sunlight
over time because of this, untill the treaters learned how to
irradiate the stones in ways which didn’t leave them susceptible to
this. And I remember when a couple years out of college, too many
decades ago, buying a lovely and inexpensive parcel of luscious rich
brownish orange topaz from mexico. Not even in direct sunlight, but
just in a gem tray in normal room light, within a month or two,
they’d faded to a pale light boring tan. Clearly irradiated stones,
though I’d been told they were natural. It was an experience that was
influential in prodding me to start gemological training with GIA…
Hope that helps.
Peter Rowe (G.G., '79)
Seattle