Rust/black spots on carbon steel knives.

J

johnlock

Joined
Jun 9, 2010
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Will Carbon steel turn black and rust a bit even if it is oiled?I have a couple of carbon steel knives that now have some brown and/or black spots on the blade, even though I oiled them after use. They are used only once or twice. It is only on the surface.
The knives are:
-Kabar USMC (the classic one)
-Ontario SP6
-Cold Steel Bushman
-A Norwegian sami knife
 
Yes it will if there is some water particle (or moisturizer) trapped between the blade surface and the oil. In my experience, oiling the blade is not really necessary as long as you keep the blade dry after each use.
 
Will surface rust like this be dangerous to the blade, will it spread? I have now washed the knives, dried them with paper towels, and let them sit for 1/2 hour, and then oiled them and put them away.
 
It will not harm the blade in anyway except may be aesthetically. It doesn't spread either.

Removing it is very easy. Put some metal polish (I use Flitz, others use Simichrome, and so on) on a clean rug, start rubbing the area where the rust is, and it should be good as new.

To prevent rust, you can put some patina on the blade surface. This patina will act as a protection against moisturize which usually causes rust. Easiest way is to rub the blade with lemon / cut garlic / mustard. This patination only works with carbon steel blades.
 
In my understanding WD-40 is a good lubricant, nothing else. I am not sure what you can gain by using WD-40. Perhaps other forumites will contribute to this WD-40 ?
 
Flitz will not scratch the blade. However, you must be careful with the rug that you use. If there is some sand or hard material trapped in the rug, rubbing the blade with the rug will scratch it.
 
Alberta ED suggested a Breakfree CLP, I thought maybe WD40 could be used instead since it is a water Displacer.

Thank you very much beluga. I will think about getting some Flitz, but since it doesn't damage the blade, it doesn't matter if it's there. Maybe it will wear of too.
 
I will get some Flitz and try it. Doesn't seem like it sold in Norway, but I'll order it from the US.
 
Pleasure is all mine Sir. You don't have to get Flitz. There are a bunch of other brands that serve the same purpose. Flitz and Simicrome are examples what people in this forum usually use.
 
I suport everything beluga has said.

The dangerous rust is red. Not brown, red!

The black spots are corrossion too, but they do no harm to the blade. A patina is formed by using the knife from any material, vegetables, onions, fruits. A patina is helpful, more helpful than a shining blade. ANy carbon blade, used for food preparation reacts with the juices. That smells and tastes. A patina stops that.

My edc blade is blue, brown and grey with some black spots.

It has to be so.

I wouldn´t spend the money on Flitz and won´t oil the blades so much. Keep them dry after using.
 
Blop said:
I suport everything beluga has said.

The dangerous rust is red. Not brown, red!

The black spots are corrossion too, but they do no harm to the blade. A patina is formed by using the knife from any material, vegetables, onions, fruits. A patina is helpful, more helpful than a shining blade. ANy carbon blade, used for food preparation reacts with the juices. That smells and tastes. A patina stops that.

My edc blade is blue, brown and grey with some black spots.

It has to be so.

I wouldn´t spend the money on Flitz and won´t oil the blades so much. Keep them dry after using.
Click to expand...

Good to hear! Thank you!
But I can't do any harm with oiling them?
 
beluga said:
In my understanding WD-40 is a good lubricant, nothing else. I am not sure what you can gain by using WD-40. Perhaps other forumites will contribute to this WD-40 ?
Click to expand...
WD-40 was originally developed as a water displacement and cleaner for aircraft. It also has light lubricating properties and does prevent rust. You will be fine using it. I use it, my father used it and several notable knifemakers use it for everything from drilling, cleaning to lubrication.
 
The blade is oiled. I mean, if the knife is used and you like to eat an oiled apple. :D

Oil is not bad, never. But in edc use my blade does not need it. It gets its share every day by buttering sandwiches after i had cut sour things. Cut first the sour and after the fat things, that´s all for protection.

In fact, i have cleaned my stainless blades after using more, than the rusting blades. Don´t know why. Never had a problem.
 
beluga said:
In my understanding WD-40 is a good lubricant, nothing else. I am not sure what you can gain by using WD-40. Perhaps other forumites will contribute to this WD-40 ?
Click to expand...

WD-40 is a mix of solvent and lubricant.

The solvent is what serves as the 'water displacement' mechanism. Other solvents, like isopropyl alcohol (rubbing alcohol), will do the same thing.

As for WD-40, after the solvent displaces the moisture from the surface and pores of the metal, it will evaporate. A little bit of lubricant is left behind as a rust preventive. It's a pretty light coat, however. If you are going to rely solely on WD-40, it's a good idea to use it pretty regularly.
 
johnlock said:
Will Carbon steel turn black and rust a bit even if it is oiled?I have a couple of carbon steel knives that now have some brown and/or black spots on the blade, even though I oiled them after use. They are used only once or twice. It is only on the surface.
The knives are:
-Kabar USMC (the classic one)
-Ontario SP6
-Cold Steel Bushman
-A Norwegian sami knife
Click to expand...

Do you live close to the ocean or a salt waterway? If so the salty air could be a factor. High Carbon blades will patina over time-that is, form a hard protective layer of flat gray, brownish oxidation on the surface. It's healthy, protects the steel underneath unlike rust which flakes and exposes more steel below the surface to rust again. Sometimes I FORCE a patina because it helps protect the blade so.
 
I usually use my knives to make sandwiches, so I really don't think Wd-40 will do me any good. I don't think I'm going to like my food with a tad of WD-40 taste :D

I will use it for my folders though. Good to hear that it can displace water. That's exactly what the pivots need. :thumbup:
 
beluga said:
I usually use my knives to make sandwiches, so I really don't think Wd-40 will do me any good. I don't think I'm going to like my food with a tad of WD-40 taste :D

I will use it for my folders though. Good to hear that it can displace water. That's exactly what the pivots need. :thumbup:
Click to expand...

It's especially useful if you ever wash your folders in soap & water. Dry 'em off as much as you can, and then flush out residual moisture with the WD-40. Works great.

As for your 'food knives', mineral oil (food grade) does a pretty good job of protecting the blades without the added 'flavor' of WD-40. ;)
 
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