Artillery sight slide...
 

...should it be rust blued or fire blued? How about the fine tune screws?

Rust blued, slide and screw.

Silly question from a neophyte: what's the difference between rust blued and fire blued? Is it a reference to the bluing process or the color of the final finish?

My grandfather's Arty is not in that great of shape, so I don't have a good idea of what the original bluing should look like (other than what I've seen in photos on the blog)

I've only been on this blog for a few months, but it seems apparent that this is where the brain trust of Luger collectors resides online.

-Aaron

Hi Aaron, Do these pictures help? Regards, Norm

Rust blue is a dull, even dark color and fire blue is generally a vivid, shini blue color

Rust blue is a chemical process. Fire blue is a heat treatment.

Now SALT bluing is the process that replaced rust bluing in 1937. It is a simpler emersion process much less involved than rust bluing.
Fire bluing is, like Ron said, a heat treatment process. I only recall seeing it on small springy parts.
Did we answer your questions?
dju

Some front sights and grip screws have been seen to be fire blued.

Thanks guys. Those answers help a bunch. I posted some hi-res pics over in the new collectors forum (post dated 12-18-2011 titled "1917 DWM Artillery Luger"). The overall bluing on mine is pretty rough. Either the gun saw a lot of use or just didn't age well.