Flitz Metal Polish is a non-abrasive suitable for all metals. Being non-abrasive, it's my preferred polish. It can remove tarnish, rust, water stains, oxidation, and hardened fingerprints with remarkably little effort. While Flitz is safe on metals, it can damage some insert materials, so use it carefully.
Keep in mind that not all knives should be polished. Polishing can actually destroy the collectible value of an older knife. Many older carbon-steel blades have a wonderful blue/gray
patina. That oxide layer not only speaks of age, but it is the metal's natural protection from rust. Old brass gets a wonderful deep gold color. A bit of Flitz can make these surfaces shine like new... but that would NOT be a good thing to do. Many older blades, those found on Filipino Handmade balisongs, for example, were not originally polished since the makers didn't have the equipment and supplies to polish them. With
Flitz, you can polish them brightly. But, again, that would NOT be a good thing to do.
It is very difficult to get Flitz out of the grain of wood or out of leather, so don't get it on wood or leather in the first place. It's also hard to get Flitz out of cracks other tight places on a knife including inside the joints of a balisong. So be very careful not to get it in there in the first place.
I apply Flitz with a heavy-duty paper towel (get these at automotive supply stores). I sometimes use a Q-Tip to apply Flitz in tight places.
To remove hardened fingerprints, minor rust, etc., apply a generous layer of Flitz and just let it sit for a minute or two to penetrate.
So, while Flitz is gentle and non-abrasive, it's still something you have to use with great forethought and great care.
This is another product that's kind of expensive. But, it's another product where a little bit will go a long way. The 50 gram tube for $8.99 + s&h will easily polish a hundred balisongs. But, this is also another product that, once you've got it around the house, you will find a hundred other uses for.