Is This An Error? If So What Kind Is It?

Improperly annealed planchet?

From the fine streaks on the obverse, I suspect this is some sort of mint discoloration. The streaks are probably roller marks/stains, but the brown color is a mystery. See this article for more discussion:

http://www.coinworld.com/insights/d...erstood.html

Thanks for the link, MikeDiamond.

Good article. I always learn something from you!

This is a common occurrence to nickels that get left in an acid based coin dip too long. These cleaners don't always do this so it must have a lot to do with the strength and how much copper has been leached out of coins that were dipped earlier.

Though it would seem like the entire coin would get the same look, what I've found when stripping toning or any oxidation at all off of reproduction cents that I "brown-tone" for customers (with Deller's Darkener) who want this service, is that the side facing up always gets stripped far faster than the side facing down. This dictates that for uniformity, I set a timer for 15 minutes for each side.

I've done a few of the reproduction nickels for customers who want them darkened (I have a special formula for that) and when left too long, I can get this copper streaked look that is virtually impossible to remove.