High carbon steel kitchen knives have a performance advantage over stainless, they do require some care to prevent rust but it does not have to be as complex as some would have you believe. In reality, we should be caring for all of our knives in a similar manner.
Side Note (All Kitchen Knives):
The key points with any Japanese kitchen knife are to avoid the dishwasher (as to not affect temper or the edge), wipe dry with a paper towel (to avoid rust) and be mindful of what, how and where you are cutting (to avoid chipping).
Before Use (High Carbon Knives):
High carbon steel kitchen knives will change colour and form a "patina" after use. This is an oxidization that occurs in the steel after a lengthy exposure to air, or short exposure to an acidic environment. This oxidization is completely normal, something that actually helps your knife resist rust. It is evident in colour, changing your knife from silver, to a grey, blue/grey or dark grey in appearance.
There are methods to speed up this process, known as forcing patina. It is widely recommended to do so before first use. The 2 methods which many recommend...
Heat (white) vinegar in the microwave and rub the (entire) blade with a lightly soaked paper towel. Leave this on your steel for 3-5 minutes, then rinse off and dry. You may need to repeat this process 2 or 3 times.
An alternative to vinegar is potatoes. Cut a raw potato in half and rub over your (entire) blade. Again, let sit for 3-5 minutes, rinse and repeat.
Many recommend that you wipe your blade clean with a damp cloth, then dry with paper towel after each and every ingredient is cut. We find this is not necessarily required (and is somewhat over-kill), recommending to just be mindful of acidic ingredients, wiping clean after use.
Clean your knife in warm soapy water and dry with a paper towel. The use of a tea-towel can leave a small amount of moisture on the blade and is not recommended.
Store your knives in a knife block, the original box, or better yet a timber saya. All of these methods will help keep moisture away from the steel and protect your knife from chips. Be mindful that your knife block does not actually contain water, some do put wet knives into blocks, which is obviously counter intuitive to our discussion here.
If you are storing your knife for more than a few days without use, we recommend coating them in an oil. Tsubaki (or camellia oil) is widely considered to be the best product for this task. Other oils can turn rancid and become a health hazard. It is recommended that tsubaki be rinsed off before use however.
In general, don't sweat the small stuff, these knives are performance machines that are made to be enjoyed. If rust occurs it is not the end of your knife, catching it early will make it's repair easier however. We recommend a rust eraser for this task, they work just like a pencil eraser, literally rubbing the rust right off.
As always, please contact us if you have any questions.