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Techniques for CollectorsFluorite Cleaning Process.

23rd Jul 2018 09:58 UTCSaim Khan

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Hello All,

I am new here. Can anyone guide me in cleaning process for this fluorite?I want to remove the coating on it.Thank you

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23rd Jul 2018 10:47 UTCThomas Lühr Expert

First you would have to know what the coating consists from ;)

Hydrochloric acid will do no harm to fluorite and can be used to remove carbonates and iron stainings as well.

Stay way from oxalic acid it - you would get dull faces!

The Waller Solution works well, though, and should be applicated after a HCl treatement.

23rd Jul 2018 12:15 UTCSusan Robinson

If, by "the coating", you mean the white layer on the crystals, it is impossible, since that is another layer of fluorite. The "Waller solution" is about the same as the product Iron Out, if you can buy that in your area.

23rd Jul 2018 13:38 UTCWayne Corwin

Siam

Do you know where your fluorite is from?

24th Jul 2018 01:59 UTCDoug Daniels

Agree with Susan. That white layer is fluorite, and you aren't going to remove it without totally messing up the specimen. Leave it as is.

27th Jul 2018 20:49 UTCHolger Klapproth

Super Iron Out (SIO) is the preferred method if the stains are iron oxides/hydroxides. If that is not available you can use diluted phosphoric acid to remove iron stains. Or if you have a bit of chemical knowledge you can also use a mixture of sodium citrate and sodium dithionite. Do not use hydrochloric acid as this will etch your specimen. Oxalic acid will dull it so much that you can throw it away. If the layer is fluorite with "dirt" inclusions nothing is ging to help.


Have fun



Holger

27th Jul 2018 21:40 UTCWayne Corwin

Holger


FYI

Super Iron Out (SIO) is now just called > Iron Out (IO)...

So don't look for the "Super", unless they have old stock.

But the company assures us the formula is still the same as SIO, no change there.

27th Jul 2018 22:15 UTCThomas Lühr Expert

Another addendum

The solubility of fluorite in HCl is about 20 times higher than in water. But still, this is yet practically insoluble and will not 'etch' the fluorite or generate HF in a dangerous concentration.

Although, it is very questionable that any treatment will solve the layer. It is well possible that Doug and Susan are right, but you can give a try with HCl and no risk.

28th Jul 2018 17:21 UTCSteve Hardinger 🌟 Expert

Solubility alone is not a good indicator of what might happen. The rate of dissolution must also be considered. For example sodium chloride (NaCl; halite) has fairly high solubility as measured in grams of NaCl per liter of water, but one could (in principle) quickly rinse a large crystal in cold water without seeing much change, whereas the same treatment to powered NaCl might result in significant changes. This is because the larger specimen has smaller surface area than the powder, which results in less exposure to water.

29th Jul 2018 16:17 UTCDonald B Peck Expert

Steve, I agree with what you say, but the luster of a crystal is only "skin" deep. I would prefer not to use a known solvent (like water on halite)on a good specimen, however briefly, where the solvent might change the luster. As to HCl on fluorite, I have no idea what the solubility product might be, but I am believe it is very low; and a quick wash of fluorite with HCl is probably pretty safe.


(I am a long time away from the theory of solubility!)

Don

20th Aug 2018 12:45 UTCPeter Ward

Hydrochloric acid DOES etch fluorite very badly. The stronger the solution, the worse the problem. None of the Weardale fluorite specimens are safe in hydrochloric - they etch. The only safe acid to use on fluorite is phosphoric.

20th Aug 2018 16:47 UTCDonald B Peck Expert

Peter, Would acetic acid do as well? White vinegar is a lot less expensive, I think.
 
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