Yes, enough copper in the tank will start to tint the Parkerizing a reddish orange but I know it takes a long time with many many parts gone thru it. Brass contamination happens much faster.
The point that I was making regarding not plugging barrel tubes while Parkerizing, is that it doesn't seem to make any difference. If there is ANY inside the bore, it wipes right out during cleaning like un-aged Park solution. Besides, the distributor of the solution that I use (Brownell's) specifically states: "Do not plug the barrels. When the air trapped in the barrel gets hot enough and expands enough, it can blow the plugs out which can cause a violent eruption of the solution". (Acid) Keep yer powder dry, Mac.
Tuff-Gun Finishes. The Name Says It All.
Mac's Shootin' irons