Ideally you should use a sharpening stone, but you can also use a whetstone or any other technique with which you are familiar. To help you, we recorded a short demonstration video on sharpening.
THE BLADE OF MY KNIFE IS BECOMING OXIDIZED. IS THIS NORMAL?
In all likelihood this is a Morta knife as forged. As stated above in our care instructions, the blade is not in stainless steel. It is actually a carbon steel forged by traditional methods, so the blade will acquire a patina over time. If it is not cleaned after use on food for instance, it will rust on the surface.
To remove the excess oxidization, you can clean the marks with a bit of 000 steel wool and some toothpaste. Your blade will quickly look as new again, with fresh breath too! 😉
However, after further use, the blade will once again take on a brown colour to nicest effect that will develop as you continue using your Morta.