Ogiginal vs re-blue
 

In the Luger world, I'm still green, but learning.

Is there any help you can offer as to points to look at
to distinguish a salt blued Mauser as original from a re-blue?

Hi lrb,
Well, you won't find halos on a salt blued Luger but there are two indicators you could look for, but you need to field strip the gun. They are:
1/ The L shaped link inside the side-plate should be "in the white" (unblued). This is a very difficult part to remove and even harder to replace, most refinishers don't bother.
2/ The same applies to the S shaped rear connector link that dangles below the rear toggle.
Regards, Norm

Good points Norm, I'd say that I hadn't thought of that. I do look for other signs of a reblue.
To reblue a gun you have to do what?
Smooth is over, ensure all the previous bluing is gone (means either manually strip or chemically, usually manual is also done). Once the gun is stripped, then it has to be smoothed, but not too much, too much sand paper and too fine will make it shine like Rudolph's nose.
Then you blue it - to get it to be right, you have to 'scrape' off the scales (rust), not once but numerous times. Everytime you scrape off, you are losing metal off of the markings, edges, etc.

I look for weak markings - be advised that sometimes markings are not stamped as hard as others, or the metal is a bit too hard.
In the left side 'ear' of the rear toggle, it should still show swirls of working / making it. When its too smooth, its a sign.
The edges of different parts will still be 'sharp'.
The numbers on the barrel and markings is not stamped as hard - look at that.
The bluing should be reasonably the same color, different parts blue different - so if darker and lighter, keep that in mind, although there are some times a different color, from the factory - plum on the receiver happens in later lugers.

ETC....