TANZANITE... or is it?
I would love to know why my tanzanite has changed colour!?
It started off really blue, but now 6 months later its more purple! ..any ideas as to why?
....oh, and its not just the flash or the angle, its clearly purple to the naked eye...
Tanzanite is trichroic (three-coloured), meaning each crystal has three colours, blue, purplish-red and greenish-yellow brown (bronze), whose intensity changes when it is viewed from different angles. Depending on the prominence of trichroism in each finished gem, Tanzanite's final colour is typically a combination of its trichroic hues. Tanzanite's rarest and most valuable colour is a strong daylight 'sapphire-esque' blue. The purity of Tanzanite's blue colour is accentuated by faceting a crystal along its width, not length and because weight and size are sacrificed for colour, this is inherently more expensive. Due to colour shift (a colour change in different light sources where the two colours are near each other on the colour wheel), even Tanzanite's finest pure blues will display some violets and purples in incandescent light.
A lot of people have had the same thing happen... they talk about it alot here: http://gemologyonline.com/Forum/phpB...?t=897&start=0
Thanks for the info LittleGem,
..The problem is it does not change colour like this in daylight or fake light, although it does display a slight colour change.
It has changed colour permanently! i never see that lovely blue colour any more.
I suppose i'm asking - is it possibly some kind of fake?
PS. could this happen if muck got round the back of the stone i wonder? seems unlikely to me.
Tanzanite can fade with prolonged exposure to sunlight.
ah, its only been a couple of months though, surely the colour should stay longer than that otherwise no one would bother with tanzanite!?
... i just bought 4 more tanzanites, the 3 on the display box top left (the yellow one is a yellow zoisite usually described as yellow tanzanite) and the big oval one bottom left that came with a certificate (well a report anyway - that i have verified) its 2.61cts ...
One of the reasons I love gemmology is each case is a dective story. It is not posible to do diagnosis from a photograph, but i will put my initial thoughts down;
Ihave done a little bit of checking, todate as far as I can find the is no synthetic / lab made. However heat treatment is "normal" to achieve the blue. Generally that is the limit of treatment, under normal conditions this shoul be table, bu expose to large amounts of UV it will fade ( E.g. a shop window all summer). That said in 2008 the AGL found coblt based coating designed to improve the blue. This coating proved unstable wearing off the facet edges an clearly viable under magnification. There are imitations, but these will be a different crystal material.
I doubt that it is normal color change effect. Thaznite will show color change, but that requires a change in the light source, and/or a change in the view point relitive to the cristal axis. in the photos the crystal is in the same orientation and the light source in both case is flash. It could be the camera white balance but you say this is consistent with you eye.
more information about the stone, it's source and history may provide some clues. Perhapse more interesting is what happened to the stone after it was set? Was it worn regularly? What's it exposed to washing up liquid, this stuff has a reputation for removing poor quality coatings. Has it ever been cleaned with a polish that our be slightly abrasive , or in ultrasound ? The latter can damage tanzanite coated or not.
Have a look at the back of the stone with a loupe. Does the blue still exist there? It's less exposed and may still in patches.
The is a battery of tests we could do but it needs equipment and cant be done from a photo. Never the less it's an interesting case.