Any material, if thin enough, has a certain amount of transparency. Aluminum deposited on glass at a thickness below 10 nm is easily transparent enough to see through. Mirrored sun-glasses comes to mind here.
Only on Star Trek do we find transparent aluminum. Any aluminum matrix is opaque. You can't see through it. Actually there is such thing as transparent aluminum but the power required for the x-ray...
The outer electron shell of an atom is called the valence shell. The electrons in the valence shell are called valence electrons. The valence electrons of most metals are not very well bound to the...