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GeneralCleaning Cinnabar With Iron-Out

23rd Aug 2019 08:25 BSTBart Cannon Expert

Don't do it.   I have a wonderful 4"x 6" botyroidal cinnabar from John Day, Oregon.  I cleaned it decades ago in warm oxalic.   I decided to remove the residual iron hyrdroxides with Iron Out.

Within 10 minutes the cinnabar transformed from bright red to black.  Now it looks like metacinnabar.

This is a big issue in the world of art restoration since cinnabar was a common pigment, and it converts to meta-cinnabar after prolonged exposure to the atmosphere.

I want to get my red cinnabar back.   Soaking in magnesium sulfate solution has brought a little color back after three weeks of soaking.

Any ideas of a solution or the mechanism of this color change ?

Iron out contains sodium hydrosulfate and sodium meta bisulfate.

I've used Iron Out to sussessfully clean iron hyrdoxides from siderite.  Oxalic acid corrodes the siderite.

23rd Aug 2019 13:33 BSTThomas Lühr Expert

I have no experiance with Iron Out, because it is not available here in Germany, but with sodium dithionite in buffered solution, which is more or less the same as Iron Out.
Dithionite (hydrosulfit) is a strong redictive agent that is added to reduce the Fe3+ (in the rust) to Fe2+. Only the latter can be good solved (by chelate forming).
So you have to be careful with minerals that contain elements with higher valences that can easy be reduced. 
In your case it may have been reduced to a thin layer of metallic mercury (which is black in fine disperse state). It will be hard to remove it without demage the specimen too much. You could try to dip it into nitric acid (>30%) for a few (!) seconds (!) and then rinse it.  Note the usual cautions while handling dangerous chemicals!

I am really not at all a friend of oxalic acid. It has many disadvantages, but in this case and for copper and silver minerals as well, it would been appropiate - in case of the absence of carbonates and calcium minerals (fluorite, apatite).


24th Aug 2019 05:26 BSTBart Cannon Expert

Thank you for the comment.  I'm pretty certain the black coating is not native mercury.

I lightly torched a fragment long enough to get it hot, but not melt.  No change.

24th Aug 2019 13:05 BSTSteve Hardinger Expert

Prompted by this thread yesterday I exposed a bright red Chinese cinnabar on a quartz/dolomite matrix to Iron Out powder dissolved in distilled water for about five hours. The cinnabar color and luster remained; there was no observable change. Longer exposure was not explored as sodium dithionite is generally considered to be fully decomposed by this time. So maybe the cinnabr source matters, or something else was going on.

7th Sep 2019 11:56 BSTBart Cannon Expert

My cinnabar consists of 3 to 8 mm botyroids with a fine druzy / granular surface.  There are no lustrous crystal faces.

25th Aug 2019 02:25 BSTGareth Evans

I think an article is needed which describes with pictures and potions the best method for cleaning minerals. I think a hands-on article rather than a theoretical one. I will get one going – soon I hope.I do not use any concoction from the hardware store or supermarket. You really have no idea what is in the mixture as most are proprietary products with misleading MSDS.It is best to get the chemicals and mix your own – shake and bake!!

25th Aug 2019 02:50 BSTDoug Daniels

I would think that MSDS's are not misleading as to constituents.  Federal law - the components have to be listed.  Now, I seem to recall reading a few that don't give the constituents, but they are flirting with problems, as long as it's a "simple" mixture.  Something like gasoline, too complicated to list everything, let alone the proportions.  And as far as mix your own - you'd better first know what you're doing, and then, good luck getting the needed chemicals as a private individual.

29th Aug 2019 03:08 BSTGareth Evans

Well most of the MSDS I have are not too specific about absolute contents. They usually say ‘X chemical’ 20 to 40%. As a chemist I find this information next to useless!I can see no problem in purchasing chemicals. I would avoid the big companies for two reasons, first they will probably not sell them to you, second they charge like wounded bulls. One well-known chemical supply company wanted $7000USD for 1 kilogram of 99.99%TREM Cerium. You can get it direct from China for about $165USD shipping included. Many chemicals can be purchased without problems from companies in the electroplating or chemical cleaning industries.Apart from a few organic chemicals and some chemicals used in the manufacture of illicit drugs there is absolutely no law prohibiting one from possessing and/or purchasing the chemicals.Another source is the hardware store, especially in the garden section. Many chemicals are often re-branded, and the new name says nothing about the content or the purity. For example sulphur (99.9%) appears as agriculture sulphur, and marketed as a product to lower the pH of alkaline soil. You can buy it in either 500 gram or 1.5 kilogram containers. You can it buy direct from the manufacturer but only if you are willing to buy a minimum amount of 25 kilograms. Another chemical, copper sulphate (99.9%) is sold as Bluestone, and marketed as a product for correcting copper deficiency. The garden section contains loads of other organic and inorganic compounds with purities ranging from of 99 to 99.9%.Another source is EBay. The best source is China direct, but if you live in the US you may encounter problems – there is a lot of bad odour between the two countries, and a trade war on the horizon.For those who say the access to chemicals is because of the dangers I suggest a casual walk through the garden, home cleaning and painting sections of your local box store. In these isles you will find highly toxic, highly corrosive, potentially carcinogenic and definitely poisonous chemicals available to anyone who is sixteen years of age or older.

25th Aug 2019 12:55 BSTBart Cannon Expert

One thing I didn't try is to wash and soak with clean water.  One peculiar reaction was that after rinsing the piece, the epsomite solution became lightly rust colored.  Maybe residual Iron Out.

The cardinal rule has remained the same for seventy years.  Always experiment with a minor specimen rather than something you really value.  I broke the rule.

Here's a cleaning tip that I don't think is widely known.  To clean native copper I've found that grocery store ammonia is better than acid treatments.    You can pull the piece before it gets too bright.  You can clean "to taste".

28th Aug 2019 21:52 BSTJobe Giles

Bart, I am very curious about your predicament, I use a ton of iron out, I often get black or black/green residue on my pegmatite Minerals. I found that a short soak in Whink’s Rust Stain Remover (brown bottle) works very well to remove this black stain. You might try it, but again, follow the rule, use a lesser piece. Also, when I say “short soak” I mean less than 15 min. 

7th Sep 2019 16:54 BSTSteve Hardinger Expert

Jobe, your green residue is mostly likely Fe2+ salts that didn't dissolve. Two solutions for this: (1) When the green occurs allow the specimen to air dry for a few hours to maybe a day. Often the green fades as Fe2+ is oxidized by atmospheric oxygen back to Fe3+. (2) Add some EDTA sodium salt to your iron out solution. This helps dissolve and retain in solution any iron present.

12th Sep 2019 20:07 BSTJobe Giles

That’s very likely. I will try that trickz

13th Sep 2019 13:29 BSTBart Cannon Expert

This is the only I've any trouble with Iron Out.

Mn oxide stains generally are removed in any kind of acid.

There at least three good books on the subject of mineral cleaning.
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