This area of discoloration is on a 1976 Browning A5 light 20.
It is a plumb color and is difficult to see unless the light and angle is just right. I didn't see it until a few days after I bought the gun. The gun is otherwise almost perfect. Any idea what caused this? One opinion is that it got out of the factory like that. Thanks, Ken

I've seen plumb coloring on several factory guns. It is usually caused by contaminated or worn out salts salts or improper temperatures. Since bluing is a micro rusting process, it often takes years to change color.

Is it just an area or the whole thing?

Normal aging on a bluing job over the years

Don't know about the instant case I've seen something like this from handling - surface rusting from hand perspiration. Oxpho Blue helped.

Kinda doubt Browning would let a bad bluing job get out. Unless of course it was blued by someone else.

Older Ruger 77 actions regularly turn plum color as they age. I have been told that they do so because the receivers are cast and the metallurgy is different than a forged action.

Could be when it was reblued the solution got too hot.

My Rem700 Classic .35Whelen has turned plumb color over the years. Other guns from the same era stored in the same safe have not so I assumed that the process was faulty, allowing further oxidation to Fe2O3, a plumb colored oxide.....At the end of the day, I decided that it was simplest to like it and move on.

I get that same plum purple color on Remington 700 bolts and receivers from using Brownells Oxy 7 hot blue solution. Leaving it in the bath longer makes it darker and less noticeable but it is still purple. Mel

Metal or case hardened. Every metal alloy is different. I got guns blued at Cleveland Black Metal years ago. Every gun on earth had a book volume for the steel and salts needed with temps. Books were 4" thick so if you think you can do it with one, good luck. Purple means chrome in the steel or it was case hardened.

Yep. Most often different alloys. What's wrong with plum/ purple? You prejudiced or something?

The Final Inspector in the Browning shop was a stickler about the quality of blue jobs, Browning also employed the services of an outside vendor not sure his work received the same scrutiny. I worked in the Browning gunsmithing shop for several years and had to redo a few blue jobs that did not pass muster.