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How to prevent chalcanthite from fading

Posted by Ashley Wise  
Ashley Wise July 17, 2017 04:17AM
I've had a couple of man-made chalcanthite samples, and recently acquired a "real" nature-made one.

My oldest man-made chalcanthite is now completely matt light blue instead of translucent deep blue. I got that one probably 12 years ago

My newer man-made is starting to lighten around the edges. I got that one around 4 years ago.

My newest "real" one is about a year old and hasn't faded yet.

I've read that chalcanthite is readily soluble in water and humid environments cause it to degrade.

What, if anything, can I do to preserve it? To prevent it from fading over time?

Can I restore the older specimins that have already faded?
Doug Daniels July 17, 2017 04:41AM
Actually, dry environments cause the degradation - it dehydrates (loses its loosly bound water). As far as the easy answer - you can't restore those that have degraded. Nope, no way, no how. As to how to keep them from degrading - that gets into some things that "purists" will fight you over. I have a few natural ones, and I have sprayed them with acrylic. And I know I'm going to be vilified for is what it is. The same would work with man-made samples. I have one that I grew, kept it in a zip-loc bag, it's about 15 yrs old (maybe more), and it is showing signs of dehydration (I did not spray it with the acrylic).

As to your "real" one.....what do you mean? Is there a location associated with it? (It does help) Can you attach a photo of it, so we can make an assessment? Until we can figure it out, at least keep it in a zip-loc.
Joel Dyer July 17, 2017 07:28AM
I grew "chalcanthite" in around 1980 - that's 37 years ago - and still have 2 nice crystals left, see below for a quick photo of one. This crystal is a bit damaged, due to rough accidental treatment. It's now in my open mineral shelf in a mostly heated office.

Many years ago, I decided to protect the crystals by spraying from afar a very thin, misty layer of lacquer onto the crystals. A layer which, BTW, doesn't affect the Raman spectrum due to it's thinness, my default used objective and the focusing method.

The crystals had before their protection been stored in alternating dryish and dampish conditions varying from -30 to perhaps +35 degrees, before they were "re-discovered" with a "mess" of other mineral samples in a cupboard in my parents garage. I guess the survival of the crystals were made possible due to them being left in peace in the darkness of the drawer, which was not fully air tight, though.



Edited 2 time(s). Last edit at 07/17/2017 08:21AM by Joel Dyer.
Alfredo Petrov July 17, 2017 07:38AM
Doug is right, Ashley. Your chalcanthites need humid air (but of course no direct contact with water).
Thomas Lühr July 17, 2017 01:03PM
If your specimen is only coated with a thin dehydrated layer it is possible to restore it (partly). Perhaps you will have to live with a bit loss of quality, such as rounded edges, though.
Hold it for a few seconds in the steam over boiling water, to generate a thin(!) film of water on the surface. Then store it in a sealed jar for some time. When the blue colour is back (it takes a while), then remove the lid and cover the jar with a sheet of paper, to let dry the rest of the water SLOWLY.
This procedure has worked fine for me with a natural specimen.
I'm storing it in a box together with a smaller box filled with wet cotton, that is also used (upside down) as a stand for the specimen.
Ashley Wise July 20, 2017 01:55AM
I attached pictures of the three chalcanthite sample

Doug Daniels July 20, 2017 03:46AM
The first one may be beyond help, although you might try Thomas' suggestion - it may work. The other two don't look so bad. It's up to you whether to spray them with an acrylic, or just try keeping them in a more humid environment. The strange thing with natural specimens is that some seem to dehydrate quickly, some only slowly, and some don't seem to give a hoot and stay the way they were found (unless put into 100+ degrees with no humidity). So, for the second and third, I'd say keep an eye on them (every few months), and if it looks like they are changing, maybe consider the acrylic (or other method, if anyone knows of one).
Alfredo Petrov July 20, 2017 05:31AM
Chalcanthite is a quite stable mineral unless its environment is much too dry. Natural samples that appear to be altering rapidly may turn out to be Pisanite (Cu-rich Melanterite) rather than true Chalcanthite.
Donald B Peck July 20, 2017 03:59PM
I have had artificial crystals turn from very blue (much like the 2nd photo) to the whitish - greenish - blue (as in the first photo) when kept in a somewhat damp basement environment.
Lawrie Berthelsen (2) July 21, 2017 06:08AM
I live in the tropics where humidity is often over 80%, and we have monsoonal wet seasons. Artificially grown crystals that I have had have gone white within 10 years, however I have had a specimen of supposedly natural Chalcanthite crystals in my collection for over 45 years which has shown absolutely no deterioration in all that time. It consists of centimetre sized crystals that have grown on a piece of mine timber, and it shows no signs of having been sprayed or coated with lacquer.

I have often wondered whether the commercial copper sulphate might have impurities that accelerate the decomposition, or whether the natural crystals might have impurities that have arrested the deterioration. I have noticed when growing crystals many years ago that a saturated solution of copper sulphate often has a greenish sludge in the bottom of the jar.
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