The Halakhot of Everyday Objects

This week's Parshah, מטות-מסעי, contains the source for the halakhot of kosher dishes.

31:21 Eleazar the priest said to the soldiers returning from the campaign: This is the rule that God commanded Moses:
31:22 As far as the gold, silver, copper, iron, tin and lead are concerned,
31:23 whatever was used over fire must be brought over fire and purged, and [then] purified with the sprinkling water. However, that which was not used over fire need only be immersed in a mikvah.

The pesukim describe that all of the metal that was captured from the Midianites must be kashered before it can be used by B'nei Israel. How is the metal kashered? The famous halakhik dictum states: כבלעו, כך פלטו. Loosely translated as, "What goes in, has gotta come out." If the non-kosher taste was absorbed via heat, then it will come out of the metal via heat.
One of the lesser known elements of these halakhot is that they only apply to an object which has been halakhically designated as a kli.

I hear a timid voice calling to me from the hinterlands of the Internet, "Oh great Kabbalah u'Maddah person, what exactly is a kli?" Wow, I am so glad that you asked that question. Quite simply, a kli is a physical object (usually a finished product) that is used by a person. The key litmus test to know whether or not any given object is a kli is: can the object become טמא? If it can become טמא then it is a kli. For example, based on the pesukim from Chapter 31 in this weeks Parshah (from Sefer BaMidbar) a sword is a kli, because it can become טמא.

Now it starts to get interesting, because a plain piece of wood (like a two by four) is not a kli because it is not a finished product. But if I take this piece of wood, put it in a lathe, and 30 minutes later I have a baseball bat - which is a kli. One more example, a tree branch lying on the ground is not a kli. But if I take the tree branch and use it as a walking stick - behold I am holding a kli! (Note - the halakhot of kelim are quite complicated and you should consult your LOR for any הלכה למעשה questions, which are mainly related to טבילת כלים . Certainly you could (and should) ask your LCR the same questions, but I don't want to further complicate your lives.)