Is it possible to “conserve” a copper coin the color of dark chocolate (or darker) to make it a milk chocolate color?
Not without damaging the surfaces. The intentional lightening or darkening of copper coins usually ends badly.
Copper, just like silver and gold, can be dipped. So the answer to your question is yes. There are a great many copper coins in slabs with the designation Red. But yet when viewed today the coin would obviously no longer qualify for that designation. Instead, if graded today the coin would grade Red Brown or Brown. In other words, the coin's color has changed in the slab - the coin has toned while it was in the slab. Now many of these coins are 50 to 100 years old or older. But yet they were given the Red designation when they were graded. So how is it that the coin managed to stay Red for 50-80 years, or longer, but then turned Red Brown or Brown in just a few short years while in the slab ? The answer is they didn't stay Red all those years. The coins were dipped before graded thus allowing them to get the Red designation. But the coin re-toned while in the slab. This is why NGC, for many years, would extend no guarantee whatsoever on the color designation of copper coins. And then when they decided to change their policy, would only offer a guarantee on the color for 10 years. It is also why PCGS no longer offers a color guarantee on copper color at all.
Thanks all, that’s been my experience too, but thought there may be some new techniques used today by conservationists.
Like Badthad says, many times it end badly either immediately or in a few years. If you dislike the toning, sell it and buy one you like. I for one actually like dark toning, and have many darkly toned large cents. I know you need a stronger light to see them, but to me adds more character. Plus, with a toning most people don't like, you are probably getting a more original surface coin. This is the same reason I collected toned coins way back, for the more original surfaces and higher luster.
I don't know of any dip or brightener that doesn't have an unworldly effect on red copper. It is usually easy to spot and the TPG's are ruthless about BB'ing them. While I am certain that there are many coins in TPG holders with a red designation that are no longer red, and also understand why NGC and PCGS will no longer guarantee copper color forever (copper is pretty unstable), there is no question that there are numerous original red coins that are many, many decades old. Shoot, an OBW roll from the 1960's or earlier is commonly filled with bright red cents looking as fresh as the day they were minted. It all comes down to how coins are stored. As for the OP's question about turning a dark brown coin milk chocolate color, certainly it can be done. Many large cents has been recolored, not necessarily to make them mint red but for other eye-appealing reasons. I wouldn't recommend it. Lance.
