Alchemy is the very old study and philosophy of how to change basic substances (such as metals) into other substances. It also studied how substances  were related to magic and astrology.

People who studied alchemy were called alchemists; they’re mostly known for a desire to change lead or mercury into gold, creating the philosopher’s stone, and the “elixir of life”.

Alchemists believe that substances, mind, philosophies, religion, magic and astrology are related to each other. 

Modern alchemy is not limited to changing one metal to another. Modern alchemists believe all things can be transmuted.