Agreed. I've only tried hot and cold peroxide soaking, so far.
Suggestions?
NOTE: There will be those that disagree with some of these suggestions. But I agree with cudamark - what do you have to lose?
I wouldn't use these techniques on a coin that had a chance of identification without their use.
If someone handed me a coin like that here's what I'd try:
1. Andre's pencils. Less than $20 on Amazon, they're my go-to tool for cleaning corroded coppers in 2021. On that coin I'd use the pencil tool then the steel wool tool. Hint: if you have toothpicks and steel wool you can basically do the same thing as Andre's pencils. Use the toothpick to see if you can remove corrosion with it. The toothpick will probably be softer than the corrosion, so the toothpick will wear away. Use a dry toothbrush to clear the shavings. Then take 000 gauge steel wool and twist it into the shape of a pencil. If you can get the twist of steel wool into something like a straw then you can hold it like the pencil. (this last part is a theory; I haven't done it).
2. vinegar for a short period of time. It's more aggressive than peroxide. I'd be looking to see if it breaks down any of the corrosion (but from your pictures I bet it won't). Or try #3.
3. ketchup. It's milder vinegar, but the reason to use it is that it can be applied to one side without getting the other side "wet" (Not an option with normal vinegar). Sometimes I put it on the side that I don't care as much about (your second picture) as a test to see what it will do. It has to sit longer (an hour?) than vinegar (20 min?).
4. Electrolysis. When all else fails I put a copper coin through electrolysis. I don't have an Ugly Box but they're apparently great. I just use an old plug-in charger (an AC-to-DC charger, like ones for a portable radio or other small electronic device. The ones with the round silver&black plug that goes into the device. I cut off the plug thingy and put two alligator clips on the wires. If you're comfortable with this idea so far, then there are YouTube videos on how to make it work).
Be Careful though because electrolysis will damage the coin, and there's no going back. 20 minute doses is how I do it. The coin will look like crap afterward (very coppery colored) but you may be able to ID it. Example (we ID'd this as a Draped Bust LC):
Before / After Electrolysis
Let us know if you can coax an ID from it.
