EDTA Experiment - Cleaning Corroded Penny

MrSpud

Background: After reading about cleaning coins with EDTA in the book Coin Chemistry I decided to try a little experiment to see if EDTA could clean a corroded copper coin without ruining it like traditional dips are said to do (see thread titled EDTA for cleaning coins, linked below, for more info). It just so happens that I came across a bottle of powdered Disodium EDTA (Note - The book Coin Chemistry used Tetrasodium EDTA, The disodium is a bit acidic with a pH of 5.3 in water whereas the Tetrasodium is more neutral) and I just happened to have a 1948 British Penny that I won throwing knives at a Renaissance festival a few years back. The Penny was brown with green corrosion. The worst area of corrosion was a big breen spot on the reverse.

Method: I dissoved approx. 200mg of Na2EDTA in approx. 25ml of Deionized water which had been warmed for 20 seconds in the microwave. The coin was immersed in the EDTA solution for approx. 30 minutes, then rinsed with tap water followed by 91% Isopropyl rubbing alcohol.

Results: The EDTA solution with the Penny in it turned a light blue color. While rinsing the coin in tap water a black residue came off of the coin. The attached pictures show what the coin looked like before and after the EDTA treatment.

Discussion: You be the judge. I have never dipped a coin in Jewelluster type cleaners. Did the EDTA do a more acceptable job than a Jewelluster type cleaner in terms of appearance of the coin as well as corrosion removal?

Any feedback will be appreciated.

Thanks for looking,
MrSpud EDTA for cleaning coins thread

sliderider

I hate to say it, but it looks like you took away some of the redness from the surface of the coin and left it brown. Cent collectors know red is good and brown is bad. I would try to find something else that leaves the original color intact. Just my 2c.

coinbuf

Looks like it took off some of the green(PVC?) from around the lettering and date. It gives the coin a cleaned or changed look but not the dramatic pink color from dipping. Not too bad.

Chris

MrSpud

I'm thinking the green was copper chloride and the black stuff that came off was copper oxide. Copper chloride is green or blue in color and copper oxide is black in color. I see lots of dirty corroded cents in change much worse than this Penny was that look black with green crud all over them which is probably from copper chloride and copper oxide. According to the book Coin Chemistry, EDTA can make the copper oxide and copper chloride come off of the coin but it doesn't remove copper sulphide like Jewelluster type dips do.

Edited to add - The green stuff, besides maybe being copper chloride, also might be copper carbonate or copper acetate. I'm still leaning towards chloride though since sweat contains salt (sodium chloride) and Pennies so often end up in peoples sweaty hands.

Edited again to talk about the red that Sliderider mentioned - I do see something that looked reddish brown in the before pics that isn't there in the after pics. Still, it doesn't look as bad as some I've seen that I suspect have been dipped in Jewelluster type cleaners. Not really sure though.

Theop

I like the results, but I know nothing about copper.

JrGMan2004

The only problem with removing corrosion... is the surface has still been damaged... it'll remove the unsightly green, and I would think would also keep it from corroding more... but there is still surface damage to the coin...

coinbuf

<<The only problem with removing corrosion... is the surface has still been damaged... it'll remove the unsightly green, and I would think would also keep it from corroding more... but there is still surface damage to the coin... >>

You are correct but at least the corrosion process has been stoped. Consider if this was a 1877IHC; would'nt you want to save what's left of the coin?

Chris

sliderider

I admit, the stuff he used did great job at removing all the ugly green, but it also took away most of the original color and luster. Copper coins should be red and bright, not brown and dull.

Conder101

On my screen the after shots look horrible. They are dead and grayish looking. The corrosion seems to be unaffected. If I hadn't read the thread and was just shown the after pictures my reaction would have been "Ugh! What the heck has been done to those things!" If that is what EDTA does to copper, stick to acetone. I wouldn't want to touch those after picture coins with a ten foot pole unless they were rare dates and very cheap. (I'm not sure I think DIPPED copper might look better.)

ColonialCoinUnion

Interesting experiment and informative post.

I also thought the 'after' photos were not pleasing.

For want of a more scientific explanation, the coin now looks cleaned to me, and I'm confident I'd have reached the same conclusion had I not read your whole post. Inf act, I did, as I opened the 'after' photos first thinking they were the 'befores'.