Please, please, please, anyone coming across this comment, if you have an old knife ping me and wait before you do anything other than lightly oil and wipe it down
There's a lot of work that goes into preserving knives. This does not preclude using them! But there's an assumption that making old knives shiny and new-ish looking is a benefit to the knife. It isn't. If that's something anyone wants to do, I have zero issues with that because it isn't my knife.
I would hope that before anyone jumps at it, they'd check and see if they've got something rare or unusual just because some things have value beyond what they can do, or even how much they'd sell for. But that's not going to happen often, luckily.
So, OP, you have jumped in, so let's deal with what up do next.
What you have now is exposed metal. It's still got some of the patina to it, so it shouldn't be too difficult to get to a reasonable degree of stability.
See, steel oxidizes. Well, you can get steel that won't without major chemical fuckery, but even those super rust resistant steels can oxidize in the right circumstances.
When you look at a knife (or and steel or iron item tbh), not all oxides are equal. Generally, you'll have two types: stable and unstable. Unstable oxides tend to be reddish, orange, or yellow, depending on the exact composition of the metal and what environment it's exposed to. Those oxides are going to keep "eating" the steel, and they'll do it fairly rapidly if no steps are taken.
However, when you see black, gray, bluish, or even some greenish coloring with or without added texture, the oxidation is going to be slow, or in the right circumstances even non progressive. That's the kind of oxides called patina. I suck at remembering the chemistry involved, but it comes down to how the atoms interact. Point being that a patina is one kind of reaction, and having it present prevents other kinds.
So knife geeks always get upset when someone gets rid of a patina rather than treating it to improve the function of the knife. But if you aren't already a knife geek, you wouldn't know anything about it.
Here's the key to making a "high carbon" steel last. You want a clean and smooth surface first. Then you want to control how oxides form. It really isn't difficult with a new knife. You just keep it clean and oiled, don't store it in leather or fabric sheathes/cases, and use it or store it in a fairly low humidity environment with a decent coating of oil. There's fancy shit you can use for long term storage, and other fancy stuff for display, but that's tangential.
Now, you've pulled off a decent amount of patina, but you got lucky; you used mostly brass and seem to have been really light handed with the sandpaper. There's not a lot of surface scratching, and that's good because scratches are where moisture loves to gather and make rust happen.
What you want to do next is get a magnifying glass and check to see how severe any scratches that can't be seen in the picture are. If they're even and not super deep, you're good to go. If they're uneven or very deep, you'll need to even them out with some very fine steel wool or something like a 1k grit automotive sandpaper.
I'm not seeing anything in the picture that's a major issue, but it is an image that's been sent over the internet, so it might not show the scratch pattern on this end, no matter how much effort you put into a pic.
But, once you have a smooth and even surface, if you're going to use it, all you need is some mineral oil, or maybe some 3-in-1, or your favorite gun oil (I'm a ballistol or rem-oil preferrer, but almost anything will do). Just a little dab on a rag and rub it on until there's a slight shine from the oil. Not enough to run, too much is as bad as not enough in its own way
Then you sharpen and use for decades. The patina will come back over time, and you'll never need to do anything other than oil it and keep the joint free of debris.
If you're going to throw it in a drawer, holla back at me, and I'll run though my preferred options if you want.
Seriously, there's nothing damaged in that picture. There's signs of wear, use, and time, but that isn't damage, that's just a used item. Most of that, like the steel itself, you'd do harm trying to make it all shiny and new looking. Even the bolsters wouldn't really benefit from polishing tbh, and wouldn't look right if you did.
That dimpling, btw, has a big benefit. Makes the sides of the knife have little pockets when it's cutting through something wet. It won't stick as much as perfectly flat sides.
For the future, when removing rust, start with solvents and cloth, maybe an old toothbrush. Elbow grease ain't gonna damage metal at all. Brass brushes are for when that fails. But, if it isn't yellow, orange, or red, and it doesn't come off with a nylon brush and some wd40, it probably shouldn't come off at all unless you plan to force a patina (which is doable, but has issues and problems that come with it too).
Legit man, I've been a knife geek since I was a kid, and I fucked up a few knives before I found out what does and doesn't benefit a knife long term. There are times when stripping down to raw metal is called for, but you have to be willing to do what it takes to keep it in good shape after that
Edit: side note: that's an old imperial. Decent knives, not likely high dollar collectibles, but they're a fairly popular brand among collectors
