I have been researching how to melt aluminum and recast it into new designs. Now you may think that is crazy, but I have a secret cool project that I am working on and this is a necessary process to accomplish that! Anyway, there is quite a culture around this art form. You may not realize, but you can get all that you need from your local hardware store come home and build your very own metal melting furnace. At least I have the basic understanding of this now, so that if there every was a complete social collapse, I could bring back basic metallurgy!
Whenever you melt certain metals, they require a great deal of heat and some have lower melting points. For example, tin or copper would have a much lower melting point than iron. In fact you can easily separate precious metals away from more common metals by simply knowing the melting points and even during the cooling process can easily filter them so that the metals become separated.
Any process of melting metal always produces a by product from the impurities found in the metal source. Minerals found in rocks are not always pure, they are mixed with a variety of other materials. Same with metal found via recycling. If you melt a aluminum can, you are going to find various things in that can that are not pure metal. In the forging process, this by product is commonly known as dross. It is known that high temperatures will consume the dross, burning it off or at least cause the dross to float to the top of the liquid metal allowing you to skim it off the top.
In many spiritual teachings you will find reference to this concept. Trials and tribulation are linked to the fire of a high temperature kiln in which your soul (the pure metal) becomes even more pure while the dross is consumed. I have found this reference in every major religion. This analogy is ubiquitous. As humankind all learned how to melt and craft with metal, there was more than one person that jumped to the obvious conclusion that fire purifies.
So fiery trials are need to improve. Needed to become more pure in your cause. You must go through hard times to get to better times. It is just a reality. You have to melt something down in order to make it better!