Replating silver?

satootoko

More years ago than I like to remember, I learned in high school chemistry that when baking soda is dissolved in hot water in an aluminum pot, or a pot containing a piece of aluminum foil, tarnish can be quickly and easily removed from silver by immersing it in the water and touching the aluminum. As I recall, the chem prof said it was a form of replating. The method does work - my beautiful bride of 47+ years periodically uses it on her silverware and stuff.

My question to the troops is - would a silver coin given that treatment be considered as "dipped" or otherwise doctored;

nwcs

Yep, it would be considered an alteration. Plating would be characterized under "altered surfaces" and get bagged. Thing is, in your description it doesn't sound like replating but rather an aluminum plating being applied.

In any case, welcome to the board!

Neil

Conder101

Yes it would be considered dipping, no it is not a form or "replating" or plating or anything like that. The reaction that causes the tarnish to form is what is called an oxidation reaction. In the case of the standard acidic dipping you are shifting the reaction back in the direction of the reduced oxidation state through the use of a more active oxidzer. You baking soda and aluminum pot are doing the same thing but in a basic or high pH solution rather than an acidic or low pH solution. Both acid and base solutions can be corrosive and eventually will do damage to the surfaces of the oin.

Libertad

Works better with washing soda than baking soda (sodium carbonate rather than bicarbonate).

I've tried it on dark Buffalo's and it does improve the brown ones, no effect on the black ones.

Here a Link with before and after pics from a coin digger-upper.

satootoko

<< <i>do damage to the surfaces of the oin >>



What's an oin ?

Seriously, thanks for the response. Guess I won't try it!

dorkkarl

replating of coins was a problem in the late 70's. i have seen a few, actually kind of a kool look.

K s

Conder101

<< <i>What's an oin ? >>



A coin with the "c"orrosion/toning removed by dipping.

Steve27

Once again Conder hits the nail on the head, this technique is NOT replating.

edsondl

The process is electrolytic in nature and not pH based. Based on electrochemical potentials and the difference in potential between silver sulfide and aluminum sulfide, an electron from the neutral aluminum metal travels through the sodium carbonate solution to the silver sulfide which reduces the silver atom and frees the sulfur ion to react with the aluminum ion forming aluminum sulfide. Now, the problem is that silver-copper coin metal does not behave the same as pure silver, so this reaction works very well for SAEs but not Mercury dimes (I know, I have tried both), but it is designed for silver sulfide and not necessarily other silver compounds (oxide, hydride, etc.-please consult your chemistry books or CRC for electrochemical potentials). Similar reactions can be done using applied voltages to overcome the passive differences in electrochemical potentials.

keets

Geez!!!! all this heady talk makes me realize why doctors are so active in the hobby. to think of actually doing this kind of stuff......................

al h.

Jdurg

Hehe. As someone who is very well versed in chemistry, these types of threads are quite interesting to me. In order for something to be 'plated', the metal being plated has to be in solution in the form of ions and then come out of solution either due to chemical means or electrical. If you have a solution of silver nitrate and put a copper penny in there, the silver will plate onto the penny by replacing the copper. If the metal in solution is 'more reactive' than the metal not in solution, then electricity will need to be used to "reverse the flow". (The electricity makes it favorable for the ions in solution to form the pure metal again instead of staying in solution).

With the aluminum/baking soda thing, you're not plating anything. Intead you're breaking down the silver-sulfide ionic complex and reforming the silver metal. The silver metal will then show through again like it did originally. However it won't be bonded to the bulk metal in the same manner so the same luster and shine won't be there.