I'm not sure what you mean by thick, as bluing isn't like an actual coating of anything. The only thing I can think of is maybe the gun finish is wore and when you take the grips off, the protected area that the grips covered looks in newer condition.
I'm sure others can give you a better explanation, but you will first get told that this thread is useless without Pictures!
I'm sure others can give you a better explanation, but you will first get told that this thread is useless without Pictures!