Use clean, untreated hardwood pieces, coconut shells, or nutshells
Dry the material completely
Place it in a metal container with a tight-fitting lid
Make a small vent hole in the lid
Heat the container in a fire, grill, or kiln until the material turns into char
Let the container cool completely before opening
Crush the char into small pieces or powder
Mix the char with a strong activating agent such as calcium chloride or phosphoric acid
Soak the char in the activating solution
Drain the excess liquid
Heat the treated char again in a kiln or oven at high temperature
Rinse the material thoroughly with clean water until the water runs clear
Dry the activated charcoal completely
Store it in an airtight container