I was trying to use $\ce{HCl}$ (muriatic acid) to remove chrome plating from plastic chrome plated shower parts (shower head holder) in order to make chromium chloride. I understand that in chrome plating, the order of plating is generally, copper, then nickel, then chrome. I also know that chrome and nickel dissolve in $\ce{HCl}$, copper doesn't. Or isn't supposed to very quickly at least. I let the parts set for several days to a week. and the parts were white, so everything was removed.

The chrome came off, but much off it came off in little flakes. Apparently the nickel is removed also. But also the copper. I filtered the solution to remove the black residue and save the chrome flakes and put them in a beaker of fresh $\ce{HCl}$.

Doesn't seem to do much. Why?