A friend of mine has warned me she intends to bring me a knife for some attention. It needs sharpening, but also has some marks. Too much touching the blade and not enough (if any!) oiling.
Gentle Rust Removal
If you paid attention in Science class you will know that you can remove rust with acids such as vinegar. Often this leaves a discolouration, however.
An interesting technique I have used is to remove rust with pineapple juice. Pineapple juice is a very mild acid. If you soak a blade for a few days it gently removes rust patches, leaving much less discolouration. Something like a vase is ideal. Just submerge the blade in juice to the depth required. If you lack a vase then the juice carton itself may be a suitable shape. You may have to brace it so the weight of the knife does not cause it to topple over.
I have only ever used pineapple juice for this, but other fruit juices should work. I suspect grapefruit juice may be too strong, but that is just a guess and I may be wrong.
Fruit and Bread Knives
I was watching a movie recently and a character makes a comment about the wisdom of cutting tomatoes with a bread knife. I guessed this may have been due to most people not having genuinely sharp kitchen knives, but I ran the idea past a chef friend.
My chef friend agreed one should cut tomatoes with a bread knife, and that it should also be used for other acidic fruits such as lemons and limes.
His explanation was that the acid of the fruits prematurely blunted other types of kitchen knife. The serrated edge of a bread knife was less affected by this. He did note that many chefs he had worked with were unaware of this.
So, if you are cutting acidic fruits in your kitchen, reach for a bread knife or serrated blade, preferably one of stainless steel.