[Scorch]

The blued finish on your rifle has degraded to the point of being "patina", i.e. a polished oxidized surface. The original factory finish was hot tank caustic bluing, and as such involves the use of high temperature highly caustic concentrated metal salts baths to convert the surface iron molecules to a stable form. This colors the metal a dark grey or black and slows any rusting. This is a hazardous process done by trained people with proper equipment, and not a home hobby project.

Home bluing is typically a cold bluing process, involving solution or gels containing acids that react to form a coating on the metal surface. If done well they can look anywhere from lousy to OK, but cold bluing solutions were originally intended as touch-up solutions for hiding scratches.

Occasionally, people who intend to blue metal at home go to the trouble of learning how to rust blue, and this involves a certain level of skill and care, but is only minimally hazardous.