Ross Bayonet blade discoloured?

[Rucker]

Would anyone have an opinion on my second from the top bayonet? Specifically the colour/shade of the bayonet? Comparing the blades of my others, it has an obvious difference. Was it cleaned/polished or is that a natural patina of the metal?
Thanks.

Information

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[Aragorn243]

Kind of hard to make that determination from a photo. Could just be it was better protected than the others.

[browningautorifle]

I agree, it could be any number of things...one that comes along is dried motor oil. The old guys didn't care, oil is oil...so a liberal coating and then it dries like varnish leaving a coating much like the one we see here. Try a mineral spirit and see if it cleans up.

Another thing it could be is a rust removal liquid, like Naval Jelly or others. There's rust present elsewhere and some pitting so perhaps a bit of judicious cleaning was done. It will leave a color like that too...

[Flying10uk]

Could it be some sort of leather "treatment" that a well intentioned enthusiast has applied to the scabbard but didn't think to remove the bayonet first? The leather "treatment" soaking through the leather then reacting with the steel blade.

[old-smithy]

could be that it is sandblasted and not polished, ?

[Flying10uk]

Could be sandblasted, but it's a job to tell from the photograph.