Removing corrosion from ancient/medieval silver coins - Initial findings

Sullykerry52

I recently made a stab at medieval coins purchasing a group of silver coins that showed significant corrosion. I researched on line to find a way to clear the corrosion to better identify the coins.
I ran two test groups:

One group I placed in olive oil, as the oil is acidic. The coins have sat in olive oil for four days. I removed them this morning. After drying the coins with Q-Tips, the corrosion was only partially removed.

The Second group I placed in a jar for three days containing 50% distilled water, 25% dishwasher soap, 15% white vinegar and 10% ammonia. This formulation is also known as sudsy (soapy) ammonia. I had much better results, removing the corrosion without damaging the patina.

I can actually read some of the inscriptions and better identify the coins.

If anyone else has recommendations, please post or PM me. John

Broadstruck

<< <i>One group I placed in olive oil, as the oil is acidic. The coins have sat in olive oil for four days. I removed them this morning. After drying the coins with Q-Tips, the corrosion was only partially removed. >>



You should dry off the oil on the coin by gently placing it in a cotton cloth and pinching the coin until all the oil is gone.

Running Q-Tips across to dry is more like cleaning or polishing then removing the oil.

Sullykerry52

I will give that a try. Thank you. I am open to any further suggestions.

7Jaguars

Electrolytic reduction can also be done. Weimar White Coin Chemistry book details a bit of this....

Sullykerry52

Thanks but the coins may be a bit fragile for the process. I am still soaking them in the ammonia concoction. Now I am trying to find the appropriate references for these mid-1600s coins from Prussia, Sweden and Lithuania.

lordmarcovan

I remember discussing that lot of coins with you. Glad to hear you had some success with the sudsy ammonia treatment. That's something I haven't tried.

One thing I've done with detector finds is to heat hydrogen peroxide in the microwave (just short of boiling) and drop crusty coins into that. Plop, plop, fizz, fizz- just like the old Alka-Seltzer commercials. It's pretty effective at removing loose grime on dug material (and as I mentioned before, I'm nearly certain your bulk lot is from an excavated hoard).

Good luck on researching and conserving them. It looked like a really fun lot.

yosclimber

I remember being interested in that lot, too, and not being sure on how to deal with the corrosion.
Thanks for sharing your experiences testing the cleaning methods.