To avoid damage, always use knives for their intended purpose. We like to say, If you wouldn't bite it with your teeth, don't cut it with a knife. Coconuts, squash stems, crusty breads & bones will win a fight with your Japanese knife: don’t do it. Japanese knives will chip with mis-use, as they are harder and thinner than their European counterparts. Always slice in a straight line and avoid twisting the knife or use it a chopping motion.
Carbon steels are a variety of steel with a chromium content less than 13%. The reactivity or rate at which carbon steels will oxidize will vary greatly but care must be taken to avoid rust. Water is the primary agent of rust, but foods that have a very acidic or basic chemistry OR are high in salt will have an extra reactivity during cutting. Wipe the blade dry during heavy use and after washing (soap is OK, avoid using the abrasive side of sponge if possible.) Always avoid soaking and keep out of dishwashers.
Carbon steel will form a patina with careful use. This is a light layer of oxidation which forms before rusting - some prefer to remove it often while others like to cultivate it. We think patina looks cool and offers a first layer of protection against rust. If active,orange rust forms, remove it with the finest non-corrosive abrasive possible (coarse abrasives will invite further rust by providing places for water to sit). We like to use the mud that forms from fine Japanese finishing stones on a rag to polish off light rust; silver polishing pastes with silica will function in the same way. For deeper heavier rust, use stronger abrasives: a fine sandpaper or non-corrosive scouring powder can be helpful.
Stainless steels are a variety of alloys with over 13% chromium content. Stainless steels vary greatly in their stain resistance, but all can rust under the right conditions. Generally, higher quality cutlery stainless steels have a higher carbon and lower chromium content. This makes them less stainless than alloys developed for heavy rust resistance (such as marine environments) and can corrode if soaked or put in a dishwasher. There is no such thing as a ‘dishwasher safe’ knife there are only knives that get destroyed slower in the harsh conditions inside a dishwasher.
Cutting Boards: For stainless and carbon steel knives, we recommend using either end grain hardwood or length grain soft wood cutting boards. For extremely hard steels, dense softwood can be a better choice than hardwood as it is easier on the edges. Length grain bamboo is especially harsh on edges as are many plastic boards. Similarly, there is no such thing as a glass cutting board - we think of them as square plates that hate your knives).