I posted this over on CCF, but thought I'd post it here as well.
Earlier this month a hoard of coins was donated to the charity I volunteer for as "the coin guy". In amongst the mostly world coins were a few Australian predecimals, metal detector or other ground finds by the looks of them as they all have environmental damage. The worst-looking piece, oddly enough, was not a "green meanie" penny or halfpenny, but this silver florin:
[attachment=3146]
I thought to myself, "nobody is going to pay bullion price for this thing; they'd never believe it's silver". So I thought I'd try cleaning it up a little. I've had some success in the past at using a 5% disodium EDTA solution at removing verdigris from copper coins, but never tried it on a 50% silver coin before. After a couple of days and three changes of solution, the results surprised me:
[attachment=3147]
The obverse had some hard brown crunchy stuff still stuck to it, but the reverse was nearly pristine, with just a small tarnish spot on the roo's back and a small brown lump on the emu's back. The brown stuff wasn't going anywhere without mechanical assistance, so I scrubbed at it with a soft plastic brush and, for the really tough bits, with my fingernails. After five more scrub-and-soaks, getting better each time, the final results are good enough that I'm considering buying the coin now myself:
[attachment=3148]
It's still a "cleaned coin", and still shows scars of it's past - I think the dull grey patches are horn silver (silver chloride), which is notoriously difficult to remove. There's also pitting where the corrosion was at its worst. Yet, quite a respectable transformation in the end.
Wow Sap, that is absolutely amazing (especially the reverse).
What do you need to make up that solution? (I'm no chemist by a long shot).
A remarkable recovery on a coin that appears to have been in salt/clear water for some time.
A job well done as I had many pre decimal silver coins found like that whilst I was a mad detectorist. Unfortunately I melted all sorts of coins down and now have three rough silver bars that weigh a total of 386 grams.
Stupid me, did not separate the pre from the post so not sure of purity of each bar.
Anyway, I look forward to your "chemical mixture" as requested by previous submitter.
Excellent transformation Sap, an amazing result.
As I said, it's 5% disodium EDTA. Pretty simple to make:
per 100 mL:
- 5 grams disodium EDTA (a fairly cheap and common bulk chemical; it costs somewhere around $25/kilogram).
- 100 mL deionized water.
Ethylenediaminetetraacetic acid (EDTA) is one of a class of chemicals called a "chelating agent". Chelating agents have molecules that are shaped like nanoscopic grabbers. The "arms" of the molecule grab onto oxidized metal compounds and pull the metal right out of them, so if you've got insoluble metal compounds (such as verdigris), they're just what you need to get the metal into a soluble form. EDTA is often in the medication given to people who accidentally swallow mercury, lead, arsenic or other heavy metals, as the EDTA grabs hold of any metal dissolved in the gut and keeps it in a form that the body can't absorb, preventing heavy metal poisoning.
As you can tell from the "acid" in the name, straight EDTA is acidic; it's also not very water-soluble. Disodium EDTA is partially neutralized (though still weakly acidic) and dissolves in water with minimal difficulty. Importantly for coin cleaning, disodium EDTA won't readily attack raw metal and will also leave alone metal oxides and sulfides, so any desirable toning/tarnish on the coin suffers minimal damage. It will, however, weaken any toning layer, so this solution should only be used to remove corrosion from coins where corrosion has become the coin's major issue.
Good explanation ! Thank you Sapyx
Thanks Sap!
The 11 herbs and spice recipe is safe with me!
Again, thanks for the recipe.
Quote from: 'Sapyx' pid='66888' dateline='1423745475'- 5 grams disodium EDTA (a fairly cheap and common bulk chemical; it costs
If it comes by the kilo, perhaps you could consider splitting it up into smaller batches for members? That 200 'doses' right there.. bit of an overkill... :angel:
It usually comes in 500g bottles, in my experience. But sorry, I don't have any at home; the lab at work has a couple of unwanted bottles of it left over from an old experiment. I make what I need there. And I doubt Australia Post would look kindly on either the solid or solution being shipped in the mail.
I found three threepences in the lot mentioned in the link below -one can be seen in my photo.
The Australian ones had a severe black encrustation that did not respond to acetone and the obverse of the '61 a dark brown stain covering most of the right hand side. I had trouble to even make out the date on those two.
So, nothing to lose with such poor coins, but I don't have any disodium EDTA. So I gave them a soak in ethanolamine 12.2% applied as a foam. [This is readily available in almost any supermarket].
Came up looking much better but probably well short of Sap's effort. Still, I am happy with the result. The orange/brown on the '51 is much less noticeable to the eye.
(http://www.australian-coins.net/gallery/albums/userpics/10055/3d.jpg)
Found in a drawer (http://www.australian-coins.net/showthread.php?tid=3457)
Very impressive results