Years ago I misplaced a nice knife from a set of knives. It turned up last week in my office. A colleague, who does not keep kosher, apparently "adopted" the knife when he found it in the kitchen a few years ago, and he didn't know to whom it belonged. He would sometimes bring lunch from home and would use the knife to cut his food. I cannot make any assumptions about his food as to dairy, meat, kosher, hot, cold, etc. He did not cook food in the office, but I recall that he sometimes would warm it up in the microwave. The knife has a wavy serration (not the fine tiny-tooth type serration). Each "wave" is 5-6mm, so one can clearly see if it is clean or not. Food cannot be "trapped" in the serrations. The handle is made of a solid piece of molded black plastic. there are no screws or rivets holding it to the blade. There are no gaps visible to the naked eye between the blade and the handle where food may be trapped. My question: is it possible to kasher the knife and return it to my kitchen? If so, what is the method of kashering required (e.g. neitza, hagala, libun)? Note that libun would probably ruin the knife due to the plastic handle, which seems heat-resistant, but probably would not stand up to libun temperatures. Thank you.
ב"ה Shalom Giving all the details, made answering a lot easier. After the knife is thoroughly clean, you may Kasher the knife by Haga'la, by placing it in in a pot with boiling bubbling water and then place it in cold water. (ספר הגעלת כלים פרק יא, ח, פרק יג שא, ספר כי בא מועד פסח ח"א, עמ' קיא, קיג) All the best