1960-D Over D Lincoln Cent?

You cannot raise the grade of a coin by cleaning it. Nothing you do will be 'undetectable', and anything you do that is detected would lower the grade of the coin - not raise it.

If there is an undetectable solution for this it would go under the category heading of 'deception' - the coin is what it is - enjoy it for that.

There is actually a way to remove carbon from red copper...but it takes a lot of time, a very steady hand, and the right tools along with a LOT of experience. I don't do it, but know someone who does...and no...this coin wouldn't come close to being worth the fee.