Sedit
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Cleaning Marble
Hello everyone, long time no see, hope everyone has been ok.
Anyone, I have a question, I have a piece of polished marble that is rather old and has become stained with a large yellow stain that I assume to
likely be Iron from local water, I need to remove the stain, hopefully without destroying the finish but I assume I could likely repolish it if
possible.
I have tried Oxalic acid in the form of Bar keepers friend however that did not really work. Is there by any chance a way that I could mobilize the
stain, or even better, just convert it into a clear substance to make it vanish even though the substance is still there. Something along those lines
would likely be one of the best ways as it would not destroy the finish, I would just have to soak the stone for a while.
It's rather important and any help would be appreciated.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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unionised
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Quote: Originally posted by Frostboi  | | Did you think of putting it in some dilute phosphoric acid solution? I’m quite sure it wouldn’t damage the rock a lot. |
Phosphoric acid is sold for the express purpose of damaging calcium carbonate.
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Sedit
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Not sure thats what I am curious about. I mean, one of the test for marble out in the wild is to place Acetic acid on it and look for bubbles if I am
not mistake, that means an acid even as weak as vinegar will cause corrosion so I would think Phosphoric would as well if not faster. What I was
thinking was something I might be able to soak it in that overtime will convert the presumably Iron Oxides embedded in it into something colorless.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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unionised
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| Quote: Originally posted by Frostboi | | [ Anyways, maybe phenol could work? It won’t certainly rip off CO2 from a carbonate but will make a salt with iron. If it doesn’t work quickly you
might need to add some hydrogen peroxide in order to oxide any leftover iron that isn’t in the form of Fe2O3. |
OK, so that's two ways to make things worse.
You can make the iron/ phenol complex or Fe2O3 .
Those are both very dark colours...
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woelen
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Ferric fluoride complexes are colorless. If your marble is exposed to HF, then you may have reaction with CaCO3 as well (albeit slowly, HF is only a
weak acid, comparable to acetic acid). The reaction with CaCO3, however, forms CaF2, which is totally insoluble in water and also in acids. So,
corrosion of CaCO3 does not proceed.
With H3PO4 there is no such protection. FePO4 is colorless, but the CaCO3 dissolves. You get Ca(H2PO4)2, which is soluble in water.
I would try with 3% HF on your marble. Be careful with that. Although it is a weak acid, it is VERY dangerous for your skin, even at such low
concentrations. In some countries you can buy a cleaning product, which contains severals percents of HF. If you can't get HF, you can get NH4HF2 on
eBay.
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Sedit
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Hmm, Ty Woelen, That sounds very close to what I am looking for. At the very least gives me a jump off point.
The idea that it forms CaF2 that is insoluble seems like a great thing to be honest because as long as it strips the color I do not care if it is in
there. If the formed salt is mobile in water there runs the risk of over time it converting back to iron oxide and being back to square one. I like
the idea of it being insoluble to be honest.
Whats CaF2 stability in higher temperatures, nothing extreme, just a slow 100degree bake in the oven to remove water before sealing it.
Knowledge is useless to useless people...
"I see a lot of patterns in our behavior as a nation that parallel a lot of other historical processes. The fall of Rome, the fall of Germany — the
fall of the ruling country, the people who think they can do whatever they want without anybody else's consent. I've seen this story
before."~Maynard James Keenan
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Metacelsus
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What about EDTA? It might remove the iron
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CobaltChloride
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You can use sodium thioglycolate. It dissolves iron deposits at neutral pH and it is sold as rust stain remover (especially for clothes). Once it
dissolves the iron, it forms an intensely colored violet complex.
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phlogiston
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We have a rust-removal product here that I found quite effective and is safe to use on marble.
https://nl.hg.eu/producten/klus/hg-roestvlekken-verwijderaar
I don't know if something similar, perhaps even the same brand is available where you live, but I recomend it if you can get it.
I have repeatedly used it on a marble shelve in our shower, which becomes stained with iron from the water over time.
It contains (2-hydroxyethyl) ammonium thioacetate, which chelates iron, forming a soluble, purple iron complex which you can then rinse off. Sometimes
I have to repeat it a few times to completely remove the discoloration.
[Edited on 13-5-2019 by phlogiston]
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"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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Keras
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Doesn’t oxalic acid also form iron complexes which are water soluble? Article here
Edit: Oops didn't see you'd tried that. How come it didn't work?
[Edited on 13-5-2019 by Keras]
[Edited on 13-5-2019 by Keras]
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