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A general guide for using the Forum with some rules and tips
Sodium Dithonite, Waller solution, Oxalic acid or HCl
  
  Index -> Conserving, Preparing and Cleaning Minerals
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al mar




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PostPosted: Jul 21, 2020 04:35    Post subject: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

Hello,

I have some samples of quartz and feldspar with a coating of iron oxides.

Being quite resistant minerals, I am only used to clean them with HCl (muriatic acid), but I have read that it is the worst method since it can leave a yellow tint in the samples.

I have looked in the bibliography and those chemicals have seen as an alternative. Have you tried any of these methods? What of them has had better results for you?
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Riccardo Modanesi




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PostPosted: Jul 21, 2020 09:02    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

Hi to everybody!
I would always be cautious by using chemical substances, some of them are dangerous both for the mineral specimen and for ourselves!
Greetings from Italy by Riccardo.

_________________
Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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kushmeja




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PostPosted: Jul 21, 2020 09:10    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

If you are just looking to remove iron residue, I would use Super Iron Out - it's cheap & it's not nearly as toxic as most of the other options. It shouldn't harm quartz or feldspar whatsoever, but should dissolve most of the iron after an hour or two of soaking.
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vic rzonca




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PostPosted: Jul 21, 2020 09:54    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

It speeds the process if you warm the Super Iron Out. Contains Sodium Hydrosulfite and Sodium Metabisulfite. Always use any chemical with care. The two quartz samples are from the same pocket, one uncleaned, the other cleaned in warm Iron Out. Leaving the solution in the sun adds heat and no messing about with hot plates and such. Mineral prep is an art.


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Jesse Fisher




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PostPosted: Jul 21, 2020 10:42    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

I generally try and avoid using HCl or oxalic acid to remove iron stain, as both will leave yellow stain on drying unless you repeatedly wash the specimen in distilled water afterwards. Specimens such as feldspars and micas that have deep cleaveage fractures are almost impossible to completely wash clean. Both chemicals are also fairly toxic and should not be used without proper protection.

Sodium dithionite (aka sodium hydrosulphite) is the active ingredient in Iron Out, and will work quite well for anything other than heavy incrustations. It also washes out of the specimens much easier and does not tend to leave yellow stains. As Vic mentions, warming (but not boiling) the solution will speed the reaction, though some find the smell unpleasant. Usually a day in Iron Out followed by a day in fresh water with a small amount of citric acid will do the job. If the iron staining is heavy or deeply infiltrated into cracks in the specimen, you may want to use phosphoric acid. It reacts slowly, so the soaking time may be a few weeks, but it works well, and will not leave yellow stains, either.

Waller solution is essentially buffered sodium dithionite, and should be used on specimens such as carbonates that are sensitive to acids.
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Bob Harman




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PostPosted: Jul 21, 2020 11:43    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

Rinsing a $1000- example in distilled water seems appropriate, but for a $50- example, the distilled water is as unnecessary as mounting the same $50- example on a $100 acrylic stand!

More to the point. After the iron out soaking and thorough rinse, soak the example in baking soda (sodium bicarbonate) solution for up to several hours, follow this by a final thorough rinsing. There will be no residual yellowing.

I have even done the baking soda rinse on old examples that had yellowed after iron oxide removal years ago. The baking soda soak and rinse removed most of that old yellowing.

It should also be noted that there are many examples of iron stained quartz specimens that are aesthetic and should not be subjected to iron out.
For 3 such examples, please review the following from my collection.
In the Indiana pages of "mineral trip thru the states of the USA", the June 5 2016 posting at the bottom of page 2, the August 31 posting, just above the middle of page 4, and the March 5 2020 posting at the very bottom of page 6.
None of these examples had their iron minerals removed.

And, for completeness, it should be noted that some iron oxide coatings can be lessened or removed after water or vinegar soakings, using a high pressure cleaning gun. Bob
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al mar




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PostPosted: Jul 21, 2020 16:43    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

Hi,

Thanks to all. First yes, managing chemical products even these that are commonly used has to be done with the proper security measures that are available on the internet and on the safety forms of each products.

Knowing this, where I live Super Iron Out it is not available for sale, and the alternatives are Sodium dithionite and the waller solution, buffered sodium dithionita. I´m curious to try between both of them.

In this mindat messageboard, topic https://www.mindat.org/mesg-190434.html Rock Currier says that he had switched from oxalic to Super Iron Out.

Thanks to all!
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alfredo
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PostPosted: Jul 22, 2020 07:07    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

The common problem of hydrochloric acid creating yellow stains on minerals can be easily avoided, not by neutralizing the acid with baking soda after the rinse, but rather soaking the specimen in phosphoric acid or citric acid after the hydrochloric acid bath. Citric acid is sold in dry crystalline form for making candy, but even a strong lemon juice will work if one can't get pure citric acid.

So, in summary, first the bath in hydrochloric acid to dissolve iron oxides, then a bath in phosphoric or citric acid to complex the iron and prevent it from forming yellow stains, then a rinse in plain water.
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basti




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PostPosted: Jul 23, 2020 09:15    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

Well, there is a lot of hype about super iron out and lot of unnecessary hysteria about hydrochloric or oxalic acid. So to clarify some "ugly" details:

1) PRICE: SIO/sodium dithionite is about 10x more expensive then hydrochloric or oxalic acid, also citric acid is about 3-4x more expensive and phosphoric acid can damage some specimens and its not cheap or easily available either.

2) AVAILABILITY: Getting citric acid is very easy, hydrochloric usually too (any hardware store). Getting SIO in most of the Europe is pretty difficult and you can usually buy sodium dithionite from special lab shops. Not that easy because of regulations.

3) SPEED: Hydrochloric removes stains within hours, oxalic within few days. SIO often takes months to properly clean specimens. Thin coatings on hard minerals like quartz can be pretty fast too.

4) DANGER:
- Hydrochloric (35%) produces corrosive fumes. Yes, it is very stupid to pour that into your eyes or drink it. Nobody sane does that. Breathing fumes is quite unpleasant up to quite painful experience, but not really a huge problem, you will not inhale that second time. Even if you put naked hand into concentrated hydrochloric, it will be a little unpleasant or itchy if you have some skin injury, otherwise no instant damage. If you spill that on yourself, calm down, wash properly, no problem. Don't put your face in the fumes, use it in properly ventilated lab (not bathroom!) or outside, no problems.
- Oxalic is toxic, but it produces no fumes, no smell, you can use it even inside. Unless you eat few spoonfuls or drink a liter of oxalic solution (very untasty), you are fine. Its very weak acid so no big issue with etching the skin, but because of its toxicity it's better to avoid skin contact.
- SIO/sodium dithionite is not directly toxic but its strong reducing agent. It produces stinky odor which is also pretty unhealthy, not good to have that inside. The fumes produced include highly toxic H2S and corrosive SO2.

5) ADVANTAGE/DISADVANTAGE:
- Hydrochloric is very cheap and fast for clean quartz specimens (no other minerals). It can remove both calcite/carbonates and rust. Iron(III) chloride is that yellow stain produced, some cheap hydrochloric is even slightly yellow (traces of chloride). As Alfredo pointed out, you can remove the yellow stains by extensive water soak or by citric acid. Hydrochloric is pretty strong and damages other minerals like micas, feldspars etc. = big nono.
- Oxalic is also pretty cheap and you can avoid fumes of hydrochloric. It also produces yellow salts, also can be removed by soak in citric acid (this time only water does not help, oxalates are insoluble in water). It is less aggressive then hydrochloric but also could damage luster of micas or feldspars - especially when used in hot solution.
- SIO/sodium dithionite is damn expensive (in EU) and slow. It is very gentle and can be used to remove iron stains even from calcite without etching it too. The disadvantage is formation of various insoluble green/black coatings, very hard to remove (more and loooong soaks in SIO or citric acid). The real nightmare is formation of secondary sulfides or silicates, as these can be removed only by blasting. SIO is great on iron oxides and can remove even some hard manganese oxides. On the other hand, it does not work that great on iron-rich clays - often forming ugly dark coatings almost impossible to remove.

The conclusions above come from real world experience - I use all mentioned chemicals regularly. The selection depends on the mineral(s). No mercy with pure quartz, hydrochloric (or oxalic indoors) + short bath in citric after. More sensitive minerals go into sodium dithionite.
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al mar




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PostPosted: Jul 26, 2020 12:34    Post subject: Re: Sodium Dithonite, Waller solution, Oxalic acid or HCl  

Hello, to all,


Thanks for the guidelines! I started with the cleaning and preparation, we will see the results.

A last question. What andvantages/disadvantages has the Waller solution (Sodium Dithionite+Citric acid/Sodium Citrate + Sodium Bicarbonate) versus only Soudium bicarbonate?

Kind regards
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