Using electrolysis to remove rust from blued item?

I have been using the electrolysis method on a variety of rusted "vintage" metals with several finishes, always with a satisfactory to a great result. However, after my latest electrolysis project on a blued item I have become much more cautious.
I had this original (genuinly blued) Haenel magazine that came with my MP44 (also Haenel) that showed some moderate pitting filled with rust. Just the kind that stood out a bit too much so I decided to give it a "bath". I always use the slow method applying a low current. After a couple of hours a good amount of rusty sludge had attached itself to piece of sacrificial metal, so I decided to take out and clean the mag. After cleaning, I applied a good amount of gun cleaning oil to the magazine. The rust in the pitted areas had gone alright but to my surprise, the cloth I used to apply the oil with became more black with each stroke. I came to a point where I clearly noticed that the blued surface (the parts that showed no pitting) started to turn more blank. Inthe end, I was looking at a very "clear" magazine with most of its blueing removed. I now just keep it soaked in gun oil now but every time I touch it it leaves some black sludge on my hands....