Too lazy to throw together a infograph but for a quick disposable knife you can melt down US pennies made after 1982 since they are zinc on any stove top and easily cast it into a clay mold. Liquid zinc is around 800° F if I'm right so it wont make the clay mold crack. Once your done with the knife reheat it and all evidence is destroyed in less than 10 min. You can also play around with alloys, since a little copper in there will make brass and although aluminum has a super high melting point it doesn't have to melt to fuse to other metals which is a unique property of it. This could also be useful in making smaller parts for more complex versions of say the slap gun