I bought a Silverton "copper" a while back, and neither I nor the seller could visually verify if it was indeed "real". I took a chance and bought it anyway.

I decided to "coin dip" it figuring I had nothing to lose, and lo and behold, nothing changed. It was later that I found looking on the outside edge, one could tell.

To the point...it looks like the mentioned cleaning remedies won't hurt the coppers. After all, the "brass" ones are basically a copper/zinc mixture and the "copper" ones were created only because reportedly, the mint got the percentages off a little. What I still don't understand is if that is true, why does the copper look layered. Maybe the pressure of the die hitting?