EDTA for cleaning coins?

MrSpud

I read the book Coin Chemistry the other day. It was pretty interesting. Lots of stuff about preventing tarnish and interesting experiments such as testing how well coins in different holders and slabs hold up in experimentally induced high sulphur atmospheres. Another topic it covered was the different methods of cleaning coins and what effects the different methods have on the surface of the coins. One method involved using EDTA to chelate some types of corrosion off of the surface while leaving the uncorroded surface as well as any sulphur toning intact. Has anyone ever tried this on a toned coin with corrosion spots? Does this work?

Shamika

That's a new one.

coinbuf

What is EDTA?

Chris

Senlathiel

Wow, who would think I'd come to a coin forum and hear about EDTA. We use EDTA in our lab, it is typically added to solutions when you want to inhibit enzymes that might digest DNA or RNAs. Most enzymes require free ions in the solution, EDTA works by chelating (sequestering) them out of the solution, preventing enzymes from using them. What effect this might have on coin corrosion, I don't know. I guess if the corrosion was composed of oxidized or charged particles, it might help them dissolve off the coin more. Buy some from Sigma or another company that supplies chemicals to labs and give it a try--I recommend that if you want to experiment with this, but not buy a lot at first, to try buying a concentrated form of TE (20x or so). TE stands for Tris-Cl and EDTA. The Tris is only there to be a buffer, keeping the solution near a neutral pH (EDTA is basic in solution--if you go with making your own EDTA solution, make it 0.5 M and then pH it down to 8.0 with HCl). The EDTA will be around 120 mM concentration in the 1x TE. If you want to explore higher concentrations of TE, just don't dilute down to 1x, maybe 5x or 10x.

bearcave

<< <i>Wow, who would think I'd come to a coin forum and hear about EDTA. We use EDTA in our lab, it is typically added to solutions when you want to inhibit enzymes that might digest DNA or RNAs. Most enzymes require free ions in the solution, EDTA works by chelating (sequestering) them out of the solution, preventing enzymes from using them. What effect this might have on coin corrosion, I don't know. I guess if the corrosion was composed of oxidized or charged particles, it might help them dissolve off the coin more. Buy some from Sigma or another company that supplies chemicals to labs and give it a try--I recommend that if you want to experiment with this, but not buy a lot at first, to try buying a concentrated form of TE (20x or so). TE stands for Tris-Cl and EDTA. The Tris is only there to be a buffer, keeping the solution near a neutral pH (EDTA is basic in solution--if you go with making your own EDTA solution, make it 0.5 M and then pH it down to 8.0 with HCl). The EDTA will be around 120 mM concentration in the 1x TE. If you want to explore higher concentrations of TE, just don't dilute down to 1x, maybe 5x or 10x. >>




HUH???

MrSpud

Here is what the book (Coin Chemistry by Weimar W. White) says about the EDTA:

it describes using EDTA as "Type B: Cleaning solutions thatpartially react chemically with a coin's oxidized matrix atoms. Examples of what is cleaned: copper oxide, copper chloride, nickel oxide, nickel chloride, but not copper sulphide or silver sulphide."

it then goes on to give an example of cleaning a cent as follows:

"Pictured is a 1980 Lincoln cent that is multi-toned from copper sulfide and nonsulfide components. The sequestering agent in the aqueous commercial dip (the tetra sodium salt of ethylenediamine tetraacetic acid, called EDTA) complexes the heavy nonsulfide metals to remove them from the surface of the coin. what is left behind is the thin layer of copper sulfide toning. An example of this complexation chemistry is expressed in the following equation: CuO + Na4EDTA --> Na2CuEDTA + Na2O"

"After cleaning: Pictured is the cleaned 1980 Lincoln cent that was subjected to the type B cleaning. Notice that the reddish-purple coloration has been removed and the color of the original copper alloy is evidenced. However, traces of toning from the non-reacted copper sulfide on parts of the cent are still evident. The picture shows that the Type B cleaning procedure is selective in terms of the kinds of surface metal components it removes. Again, the coin was rinsed with sufficient quantities of distilled or demineralized water to remove all traces of the residual dip. The cleaned coin was carefully dried."

It has a before and after picture of the cent. The before picture shows a brown cent with a heavy greenish blue patina covering most of the coin. The`after picture resembles a red-brown cent with some blue-green toning mainly in the periphery of the fields.

I thought this was interesting because I have seen posts where people ask if anything can be done to a coin that has unattractive dark toning or corrosion on it and all the replies usually said that the only thing that could be done was to dip the coin into a jeweluster like cleaner which would strip away all of the toning and leave a pitted ruined coin. also, I never heard of anyone being able to clean copper coins without ruining them.

Iwog

Big Mac® Sauce:
Soybean oil, pickles, distilled vinegar, water, egg yolks, high fructose corn syrup, sugar, onion powder, corn syrup, spice and spice extractives, salt, xanthan gum, mustard flour, propylene glycol alginate, sodium benzoate and potassium sorbate as preservatives, mustard bran, garlic powder, hydrolyzed (corn gluten, wheat, and soy) proteins, caramel color, extractives of paprika, turmeric, calcium disodium EDTA to protect flavor.

BAJJERFAN

EDTA stands for EthyleneDiamineTetraacetic Acid

Monstavet

EDTA has many uses in the medical field. It is commonly used as an anticoagulant for blood samples when running Complete Blood Counts. It is also used as part of the therapy for lead intoxication...IT chelates the lead right out of your blood vessels and vital organs...expensive stuff.

BAJJERFAN

Also used to treat mercury and other heavy metal poisonings. Actually its dirt cheap and made by the millions of pounds tho the pharmaceutical grades cost a bit more.