It’s highly recommended to clean your knife immediately after use, before any remains of the food have dried. Additional to the fact that (depending on the steel of your knife and what you have been cutting) your knife may stain or rust, it is also a safety issue. Once food remains on the blade have dried, removing may require some force, which applied on a sharp blade can be dangerous. For cleaning, rinsing your blade under hot water and wiping with a wet cloth (and if necessary a small amount of detergents) will usually do.
It’s never recommendable to clean knives in a dishwasher: Many knives are not suitable for dishwasher cleaning due to the materials used on the blade or handle. Any knife with a handle material other than plastic or metal has no place in the dishwasher anyway, since the handle will not be fully water resistant. A blade made of high carbon steel (any steel with a carbon content of >0.6%, regardless of the amount of Chromium or if it’s called stainless) will stain, and a carbon steel knife even rust completely in a dishwasher.
However, there is a large number of knives out there that could be put in a dishwasher or look like a dishwasher would do no harm to them. Many German knives, with softer steel and plastic handles, are actually tested to survive dishwasher cleaning without damage and may be advertised as dishwasher safe. Also knives with stainless steel handles appear to be dishwasher safe. However, many of those have a weak zone in the welding seam area and may start to corrode there if cleaned in a dishwasher, eventually leading to breakage.
Still regardless of whether a knife would survive dishwasher cleaning, one should keep in mind that the detergents in the dishwasher are very abrasive, and will, along with the pressure of the cleaning nozzles and the high temperature in the machine, degrade your edge. Also, the banging around that happens during a wash cycle may damage the edge, or reversely the knife scratch cups, plates or even the machine. Also, there is always the risk to cut yourself during unloading.
As convenient as a dishwasher may be, KNIVES HAVE NO PLACE IN THEM!
This is for handles made of wood, natural, stabilized or Pakka. Wood can dry out, especially in dry climate. Oiling it will mitigate the effects of dryness and give the wood a saturated look.
Prior to oiling, the handle should be cleaned with a moist cloth and wiped dry. Then apply oil, either with a drained paper towel, or by hand, and rub it in. The oiling can stop once the wood no longer absorbs the oil and the handle looks wet.
The following oils are suitable for oiling of wooden handles: Danish oil, raw Linseed oil, food grade Mineral oil and Walnut oil. Alternatively, there are different conditioners, waxes and polishes for wood that can be used, like Carnauba or Bees wax. Not suitable are olive, sesame seed, peanut or coconut oil, since after a while they will oxidize and go rancid.
Carbon steel knives
Due to the corrosiveness of the blade, Carbon steel knives do need some extra steps to maintain. The steel is very reactive and prone to staining/corroding, so that the blade needs to be rinsed and wiped dry after use. The material will react very quickly especially to anything acidic, which makes is imperative to clean the blade immediately.
After washing and wiping the blade dry, oiling it with a food safe oil (any cooking oil will do) is recommended to protect the blade.
Carbon steel knives will develop a patina over time, which is a layer of oxidization. This is a good thing, as it offers some protection of the blade from corrosion. It is sometimes even recommended to “force” a patina, thus accelerating the natural processes and built the protective layer more quickly and evenly. There are different methods, like boiling the blade in vinegar (like apple cider vinegar) for a couple of hours, or even covering it in yellow mustard for a few hours.