White carbon, blue carbon and super blue carbon steel bring awesomeness to knife making that is unbeatable. Having a hardness that borders on the extreme they are capable of being sharpened to razor-like keenness, and hold an edge for a very long time.
The trade off for this wicked sharpness is oxidation. That means they could rust. Looked after properly, however, they will develop a patina long before any rust can take root.
You will find, as I have, that these blades will change colour becoming grey or even black as they are used. This is just the patina developing. Consider how a copper roof becomes green over time, or a leather jacket becomes more beautiful as it ages. This is an oxidation process that occurs with carbon steel knives, once the patina has developed the surface will no longer be susceptible to further corrosion (rust).
Should rusting occur simply use a kitchen scrubby (not copper or steel wool as this will scratch the surface) and warm, soapy water to remove anything that looks like rust.
It’s impossible to avoid some discoloration with carbon steel knives. I love to watch this develop over time and am rewarded with the keenness of the edge and the longer edge retention that you get with this quality of white or blue carbon steel.
As you use them on foods like onions, tomatoes or other acidic food you will notice that a greyish hue will develop. This is to be expected, just wash with warm water and keep dry. My carbon knives have a strong patina that I acknowledge as a reward for using exceptional knives, each blade being unique.