How To Get Dates Off Of Dateless Coins?

Very interesting info. Thank you.

Anyway, how does this process pull dates off? I would assume that the date digit area is less dense, being less compressed during striking, and corrodes in the acid more easily. Is this correct?

OK, I found the cord, so here are the before pics. I just put the coins in. By the way, I meant to say that one had a D MM, not S (the one on the right).

Post the pics here and the members more familiar with worn buff dates can tell. But make sure that you take the pic at the right angle so we can see the date lol

Yeah, telling the difference between a 13 and a 15 on an acid dated buff can be tricky at times. Definitely post a pic though and we should be able to help you out.

More acid?

It's a little more complicated than that. We're talking here about the chemistry of acid-metal reactions combining with the physics of the microstructure of a piece of metallic alloy that has been struck between dies. Here's my take on what happens.

When a coin is struck, the metal "flows" in a generally outwards direction, following the shape of the die as it presses down. This aligns and stretches the crystals within the metal in that direction of flow. If the flow encounters an obstacle (such as a valley in the die the metal has to flow down into) the crystals follow the contours of the valley. A "valley" in a die, of course, creates a raised feature (such as the date numerals) on the coin itself.

This means that, on a worn coin, in the areas where the transition between the field and the numeral used to be, the crystals are not aligned in the same direction as they are elsewhere on the coin. It is this different crystal alignment that reacts slightly faster to the acid. Thus, after acid-treatment, the transition zone becomes an etched pit between the two flat areas - which remain at the same height as each other. It is only the corrosion pit in between the two zones that causes the date to stand out.

Perhaps this picture helps explains it.



I have seen this exact same effect happen on silver coins. I was recently attempting to re-tone a silver coin where one side had been ground completely flat. I assumed all trace of the old coin would have been erased, but I found that on exposure to hydrogen sulfide gas, the now-vanished design of the coin re-appeared in outline as a toning pattern, like the ghost of the old coin coming back to haunt me.

One could, in theory, use this same technique to reveal a date on a worn silver coin, except you'd need to strip away the "natural" toning first, and then you'd have to protect the re-toned surface from further toning.