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Green amethyst loses color


#1

Hello,

Today I worked on sizing down a sterling ring with a 10mm square
green amethyst. Before I soldered the seem shut with medium solder, I
made sure I had a lot of heat shield gel all around the stone.
Everything was going like a dream until I noticed the stone went from
a light green to almost clear!!!

Man, I just love to learn the hard way…

I’m thinking I heated up a stone that never should have been heated
up?

Can someone explain what is going on here?

Thanks for your help.

-Chris


#2

Prasiolite is the correct name for the gemstone called with the
misnomer “green amethyst.” This gem can occur naturally, but is quite
often made by heating purple amethyst. If the coloring agent in the
amethyst is Fe++ then a green color will result. Experimentation has
shown that heating the Prasiolite will cause a permanent loss of
color – "K. Nassau, 1977, studied green quartz crystals collected by
E. S. Dana in Brazil in the year 1884. He found that upon irradiation
the crystals assumed a violet color in addition to the green color
already present. Upon heating to 350 C the violet color was lost,
while the green color was preserved. The green color was lost by
heating to 500 C and could not be restored by subsequent irradiation,
instead the crystals turned violet. Nassau considers the green and
violet colors to be based on structurally independent causes and the
crystals to be different

from “greened amethyst” as described in Lehmann and Bambauer, 1973.

Taken from http://www.ganoksin.com/gnkurl/ep80dg

John


#3

Sounds like me and my first dealings with Mystic Topaz, they went
clear, causing me much grief replacing them. I was reading that
Amethyst neveroccurs naturally as green so the ones we see are
either treated or coated like Mystic Topaz. By the way I protected
them and kept them cool, it wasmy acid pickle which took that coating
off. The minefield of modern stones, have fun. Hamish


#4

Properly the stone should be called prasiolite or green quartz. The
name amethyst should be used to refer only to purple quartzes.

Heating prasiolite will make it lose color. Here is some technical
on green quartz.

http://www.ganoksin.com/gnkurl/ep80dg

Elliot Nesterman


#5

Just as you say, heating the stone has changed its colour. Amethyst
can be heated to make citrine or sometimes it goes green. Generally
the heating/cooling cycle will determine colour or colour loss on
pale stones and it looks like you have been unfortunate to lose all
colour. Nick royall


#6

quartz does not support fire.


#7

Hi Chris!

I have done repairs on silver with stones for years so thought I’d
share. Always remove stones, and if they can’t be removed or there is
an inlay you must laser repair them (doesn’t heat the metal). Silver
is different than gold as you cannot heat sink stones and spot
solder. You must heat the entire piece before your silver will flow
in the intended spot. Be sure to keep it clean with the boric acid
denatured alcohol mix and flux. And I always use hard solder on
sizing seams. Good luck! Fondly, Steph Swanson


#8

First, I’m suspecting you used/fell prey to “kool Jool”- it’s junk
firstly. Second, those stones are heat treated quartzes. amethyst is
purple- its a gimmick stone and one that “is not recommended” for
steam cleaning or ultrasonics. Like many, many stones on the market
that are heat treated, vapour deposition coated (mystic anythings. i.
e.-.mystic topaz’s are coated with a thin film of metal to give them
an iridescent appearance), and even assembled (they take a sliver -
if you’re lucky) of a real gem, say emerald, and use a green epoxy
and quartz as the base and cap then cut and facet the material. It
isn’t even steamable! I bought some parcel of stones for a super
great price from a vendor a few years ago who told me the gorgeous
colour would change when I heated it into a much deeper shade! Well,
i was curious, and sure enough, just the heat from casting it made
the material (which I’m still uncertain what it actually was, but was
sold as ’ natural spinels’) change hues. The catch was unless you
wrote down the exact time at x temperature you got that first result
(that you liked) it was difficult to match. particularly since the
supplier told me a lot of people that “do” metal clay like these. So
there you have it. some stones out there just aren’t what they are
sold as due to the gimmick stones and trickery, frankly, salespeople
use at Tuscon and other big gem shows to move material that wouldn’t
otherwise sell as irradiated quartz !


#9

Thanks for the feedback from everyone. this is one of those mistakes
you make and never do again. hopefully.


#10

“Prasiolite” or green quartz, may be irradiated and the color will
fade in light. Heating will also change the color. This color does
not normally occur in nature. It’s another gimmick.

Jackie


#11

I have found the last three smoky quartz rings over a 10 year span
all went colorless after I sized the sterling rings. As a result, if
I have to size a ring with smoky quartz, I make a new ring. Still
waiting for new trillion settings from Stuller so I can finish yet
another smoky quartz ring for a client.

I now have a brilliant green quartz (from JTV - I did not buy this
stone), that is in a ring, that needs to be re sized, and I’ve been
putting it off, for I don’t want to waste yet another trillion
setting, but I have to bite the bullet and just take stone out, size
ring, replace the setting and put stone back in. Or make new ring -
whatever is easier.

I hate quartz now for it causes more problems than it is worth, but
still have to work with it for clients prefer it.

I use Heat Shield (from Gesswein) for every other ring I size.
Airgas has a product called Heat Fence that is virtually identical
to Heat Shield, so my guess both are the same product, but
repackaged. As a last retort, submerge stone in a container of
water, supported by two third hands, and an oxy/acetylene torch to
heat the shank fast and get the solder to melt. I did that for a
lapis ring when I was away on a workshop and the lapis survived.

Word of warning - anything with a quartz, don’t allow any heat on
it. Pure and simple. Otherwise, you are going to replacing quartz
more than you want to. I waste enough time trying to find identical
stones for replacement.

Joy


#12

Hi

that is why I buy from O’Neils Affilated all stones are coded

N natural
E enhanced heating, oiling waxing
T treated, impregnation, dying, irradiation
S synthetic

Now days the GIA in Oz calls it value enhancing. In the old days we
called it faking it.

Times have changed.

Had a tiger eye change to red in a shank repair, luckily the
customer liked it better and did not want

it replaced even though I had one and offered to do it for free.
Who’d a thunk that?

Richard


#13

Chris- Just thank your lucky stars it was only a piece of quartz.

Inexpensive to replace.

I watched a boss of mine in a busy trade shop once turn a custom cut
13 ct Golden Sapphire the color of water after soldering on it. I
warned him not to do it. “You’d better pull that stone before you
solder on the bezel.” He blew me off and soldered on it anyway. He
had to buy a 14 ct golden sapphire and have it custom cut to match
the one he destroyed. We didn’t get an Xmas bonus that year.

Have fun and make lots of jewelry.

Jo Haemer
timothywgreen.com


#14
Had a tiger eye change to red in a shank repair, luckily the
customer liked it better and did not want it replaced even though I
had one and offered to do it for free. Who'd a thunk that? 

I believe I have read that the red and blue versions of tiger eye
and pietersite are heated (either by man or mother nature) to get
those colors from what starts out the usual yellow. So I suppose it’s
to be expected.

Tiger eye is cheap enough-- when I get a chance, I think I’ll heat
some and see what happens.

Noel


#15

I would never put heat on a big valuable sapphire again. Many years
ago I was tipping a fine blue sapphire, it was protected with a
Boracic coating, I let it cool and then cleaned it in the acid
pickle as usual. on examination I found a piece had flaked off the
front of the stone. In blind panic I went to a professional stone
cutter and gemology teacher I knew, now deceased, it was many years
ago. I had examined and cleaned the stone before working on it, he
said that it might have had a liquid filled inclusion which blew up
when I heated. I was lucky he was able to re-cut the stone, very
cleverly, it looked perfect and fitted the original setting really
well. Thanks Dennis wherever you are, I have never heated a valuable
stone ever again. Hamish


#16

Hamish- I was taught to never put boric on corundum when heating. It
will fuse to the stone and come off in the pickle leaving an orange
peel finish on the corundum. I saw it happen in a busy trade shop in
the past where there was a newbie who didn’t know about corundum and
boric acid and the rest of us were too busy to catch him before he
did it.

Thank goodness it was a small and inexpensive saph.

Have fun and make lots of jewelry.

Jo Haemer
timothywgreen.com


#17
Hamish- I was taught to never put boric on corundum when heating.
It will fuse to the stone and come off in the pickle leaving an
orange peel finish on the corundum. I saw it happen in a busy trade
shop in the past where there was a newbie who didn't know about
corundum and boric acid and the rest of us were too busy to catch
him before he did it. 

Think about it this way: Flux, including boric acid and borax, work
to prevent metal from oxidizing, and to dissolve metal oxides that
do form. Corundum is aluminum oxide. The flux wants to dissolve that
metal oxide, so it is able to etch into the corundum when hot.
Corundum, already being an oxide, is happiest in an oxidizing
atmosphere. A reducing flame, without flux coating, can reduce the
metal (aluminum) oxide, leaving an irridescent looking surface film,
while the flux coatings that protect metals and diamonds from
oxidation, can damage the corundum.

Considerations in dealing with this are:

At lower temps, just barely enough to melt the boric acid fire coat,
If time at temp is kept to a minimum, the potential for damage is
also minimal. But still, don’t do this to valuable stones. Slight
etching may not be visible as such, but might still affect the look
of the stone. Boric acid firecoat is not as active in damaging the
corundum as are soldering fluxes themselves (batterns, or white paste
fluxes) You can often work fairly safely with just the fire coat,
but actual soldering flux is much riskier. In general, this would be
in doing repair work on commercial quality (inexpensive) stones.
Often, these stones may already have some slight damage from paper
wear or normal wear and tear, so a little slight etching of surfaces
might be completely invisible. But recognize that in the end, you’re
damaging, or risking damaging, a customers stones.

If you can work with a neutral to slightly oxidizing flame and
without fire coat or flux on the stone, then that will avoid etching
or damaging the corundum. But then you have to more carefully address
oxidiation of the metal, solder flow, etc, which will require careful
placement of fire coat (boric acid, etc.) and soldering flux on only
the metal where needed. Note, I don’t know whether Firescoff will
also etch corundum. It might be that their formula doesn’t cause this
risk, but I don’t know. That factor might easily make that pricey
product worth keeping around…

And none of the above addresses the other risks to corundum when
heating: Heat treated stones in particular, but others too, can
change color from heating.

Inclusions in the stones can cause damage. Liquid filled inclusions
in particular are disasters waiting to happen, and are not always so
easy to see.

These can cause catastrophic breakage of a stone at temperatures far
lower than any etching from flux. The single costliest stone I ever
broke was such a sapphire. Nice large (around 8 carats) heart shaped
Ceylon sapphire. I didn’t specifically heat the stone, just tried to
flow a little solder on part of the undergallery where a drill had
nicked a wire. Tiny flame, not pointed anywhere near the sapphire.
The boric acid protecting the diamonds around the sapphire never even
melted. But the sapphire got warm enough that the large, but hard to
see liquid filled inclusion caused the stone to split in half. My
boss was not happy. I’ve not taken that sort of risk again since.

Peter


#18

Dear Jo

Hamish- I was taught to never put boric on corundum when heating.
It will fuse to the stone and come off in the pickle leaving an
orange peel finish on the corundum. I saw it happen in a busy trade
shop in the past where there was a newbie who didn't know about
corundum and boric acid and the rest of us were too busy to catch
him before he did it. 

Now you tell me, I’ve been doing this for 50 years and never had
such a problem. I think we have to be very careful about heat on
stones. Perhaps I just got away with it. I try shielding stones from
the heat. Thanks for the info. Hamish