The complete build process for crystal power cells. 

Needed Items:

Solid magnesium rod.  Aluminum can also be used but will give a lower voltage.
Copper pipe cap.

Equal Parts of the following:
Potassium chloride - commonly known as salt substitute.
Hydrated potassium aluminium sulfate - commonly known as alum.
Sodium tetraborate - commonly known as 20 mule team Borax.
Magnesium sulfate - commonly known as epsom salt.

Reliance 9001829005 32-Inch Magnesium Water Heater Anode Rod

Price: $27.49


Great prices on magnesium here:

Galvanic Chart: