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al mar
Joined: 17 Feb 2009
Posts: 19
Location: Biscay, Spain
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 Posted: Aug 26, 2018 08:25 Post subject: How to "Defrost" crystals in quartz |
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Hello, I have seen some crystals "defrost" from the quartz matrix covering, and the appearance is in most cases very good. I would like to know about experiences and methods used successfully by the users of the forum.
I put a photo of a Zambian emerald as an example.
| Mineral: | Emerald |
| Description: |
| Photo by Joan Martinez Bruguera of Nat. Hist museum of London specimen. |
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Fiebre Verde
Joined: 11 Sep 2013
Posts: 942
Location: Paris Area
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| Posted: Aug 26, 2018 09:19 Post subject: Re: How to "Defrost" crystals in quartz |
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| al mar wrote: | Hello, I have seen some crystals "defrost" from the quartz matrix covering, and the apearence is in most cases very good. I would like to know about experiences and methods used succesfully by the users of the forum.
I put a photo of a Zambian emerald as an example. |
Al Mar
The example you gave is pretty well known..
As you mentioned, this specimen is part of the collection of the Natural History Museum of London - it has been nicknamed the 'Medusa Emerald' by the museum (Not sure why, the similarity with a Gorgon is questionable but that's a different story).
Here is the (short) story of the Medusa Emerald as it is related in the NHM site:
"The Medusa emerald was hidden for thousands of years inside a huge boulder of quartz rock.
Miners usually break down large boulders with a pneumatic hammer. However, Gemfields realised they would need a different approach to reveal the potentially world-class gem inside.
They sent the boulder to mineral dealers Collector’s Edge in the United States. In the world’s most advanced mineral cleaning laboratory, a team of experts used state-of-the-art techniques to uncover the treasures within.
Several months of delicate and laborious work, painstakingly removing the quartz millimeter by millimeter, finally revealed the beautiful emerald crystals"
I realize this doesn't answer your question as to the cleaning technique they have used to remove the quartz "millimeter by millimeter".
Hydrofluoric Acid (HF) is what comes to my mind but they might have used a different way to remove the quartz - mechanical cleaning does not apply in this case.
Maybe a Collector's Edge forum member could tell us the full story?
Gérard
| Mineral: | Beryl (variety emerald), Quartz |
| Locality: | | Kagem Mine, Kafubu, Ndola, Ndola District, Copperbelt Province, Zambia |  |
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al mar
Joined: 17 Feb 2009
Posts: 19
Location: Biscay, Spain
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| Posted: Aug 26, 2018 09:45 Post subject: Re: How to "Defrost" crystals in quartz |
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I have seem other samples in mineralogical shows (but it is difficult to find photos available to post) I know that some world top laboratories are working on that, but I find difficult to know their techniques by obious reasons. However, when I have tried to remove the quartz the appearance is unnatural and the other minerals are usually damaged.
HF is an option only when the "frozen" mineral is not attacked by the acid (and it is very dangerous).
Maybe someone has tried with better results.
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Bob Harman
Joined: 06 Nov 2015
Posts: 765
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| Posted: Aug 26, 2018 10:16 Post subject: Re: How to "Defrost" crystals in quartz |
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| I would not at all be surprised if the emerald portions had one or more expert reattachments after the quartz was expertly removed. If for sale, the complete label would have to state any repairs or reattachments. However, if in a museum display, repairs of any type need not be mentioned. BOB
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GneissWare
Joined: 07 Mar 2008
Posts: 1287
Location: California
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| Posted: Aug 26, 2018 10:28 Post subject: Re: How to "Defrost" crystals in quartz |
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| Quote: |
Several months of delicate and laborious work, painstakingly removing the quartz millimeter by millimeter, finally revealed the beautiful emerald crystals"
Hydrofluoric Acid (HF) is what comes to my mind but they might have used a different way to remove the quartz - mechanical cleaning does not apply in this case.
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This answer is pretty close to correct, although a few other chemicals may be involved. There was likely large amounts of air abrasion and air scribing to get material removed.
None of the labs will tell you the pressures or media they use for abrasion, or the chemicals, as those are all hard won secrets, and give them a competitive advantage. If you have something good, send it to a lab with experience. It really doesn't cost that much.
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