Alchemy is the art of changing one element into another, or combining elements in new ways, through the use of magic circles and natural processes.
There are 10 elements, 7 planetary elements (fire, water, earth, wind, metal, wood, and salt) and 3 heavenly elements (void, aether, and energy). Planetary elements are the ones that are in high quantities in planets and moons. In particular, fire, water, earth and wind are especially prevalent, making them some of the elements that are the easiest to find and classify for early species. Metal, wood and salt are still abundant on most worlds, but in lesser quantities than the other four, and are often assumed to be one of the other four that has gone through some kind of alchemical process. However, later experimentation often shows that salt and metal are both separate from earth and wood is separate from earth, fire and water. That said, while wood element IS found very commonly in plants, especially woody plants like trees, trees and plants are not purely wood element, and wood element is found in other materials.
The heavenly elements are those that are rare or nonexistent on the vast majority of planets, found much more readily in stars (aether and energy heavy), the space between a star and its planets (aether heavy), and between the stars themselves (void heavy).
Stars, being in truth powerful gods, have access to vast amounts of all elements.
Living things and their products are hard to alter or reproduce, while basic elemental things are easy. Bode's world economy destabilized for a while after they figured out how to produce gold from other metals, but now use money based on seeds, fabrics, animal products or similar, due to the security they provide against alchemical counterfitting.
