High polish on just top of 1896 receiver?

[CJN]

I have an 1896 rifle which is in very good shape a correctly dated 1896 stock. and what looks like original finish. EXCEPT, although the receiver looks like original finish all around inside the tang, the area around the magazine box and plates.
the top of reciever

(with serial and factory stamping)looks like the pic attached. polished and the opposite side next to cocking sleeve. highly polished very new looking. it's not possible to re-blue part of a receiver? this may have been polished, or otherwise coated? any ideas, as to why it looks like this? the rest of receiver matches all the Krag rifles and carbines I've seen with original blue. not super shiny, but military blue.

Information

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[browningautorifle]

It looks to me like it's been 555 polished and dropped into the blue tank as is. The rest I can see has a mottled blue which is characteristic of a hot salt blue done over an unprepared surface. If the salts are strong and fresh you can usually blue right over top of existing blue.

[CJN]

So you can add over existing, without finishing the surface all over. that's probably what someone did. I looks great but makes it look much newer and not match the rest of the rifle.
which has original blue with the two bands turning slightly plumb colored. It probably would have been better to leave the top of recover as it was even if a lot of finish missing.

Thank you,

[ssgross]

slow rust bluing works great over existing bluing to even out and darken. With a nice soft carding wheel, you can easily get the results like what you see on the main receiver around the serial. Any evidence of light surface rust is eliminated when slow rust bluing, as long as the etching from prior rust is no deeper than, say, 400 grit sanding or so. Having refinished an 1898 krag receiver to build mine from scratch, I can tell you that the case-hardened parts can be a pain, even if completely prepping the surface. This is why your refinished side plate looks different then your refinished receiver, with what looks like a little "mottling" underneath. When slow bluing my side plate, I tried multiple times to get it to match my newly finished receiver. Finally, I figured out the trick - sanding to 400 grit (like the rest of the metal), but then wiping down evenly with 10% muriatic acid for ~10 minutes.

FWIW, I think that cleaning up the finish over top of existing finish works much better with slow rust bluing then hot bluing. The layer of magnetite is typically much thicker with slow rust bluing, and so carding with a nice soft steel wheel can blend over most blemishes.

[browningautorifle]

slightly plumb colored

That's another tell when the salts dont get the parts dark...factory didn't have that problem.

slow rust bluing works great over existing bluing to even out and darken.

That's another real possibility, a clean top with rust blue. The polishing makes the difference. Just that part was cleaned off.