Alchemy

An excerpt from Ars Magica by Hermione Granger

magic smoking wine glass by Raventhorne

This is why alchemy exists," the boy said. "So that everyone will search for his treasure, find it, and then want to be better than he was in his former life. Lead will play its role until the world has no further need for lead; and then lead will have to turn itself into gold. That's what alchemists do. They show that, when we strive to become better than we are, everything around us becomes better, too.”

— ― Paulo Coelho, The Alchemist

Alchemy is one of the best known and least practiced of the Old Lores, and is one of the four Great Lores as spoken of by the remaining Loremasters.
The only known current practitioner of Alchemy is the veneral Nicholas Flamel. While he did attempt to teach Albus Dumbledore, that wizard, for all his power, did not have any aptitude for it.

There is a great fear that this Great Lore may die out if new apprentices are not found.

Thankfully, anyone who can access Lore can learn some basics of Alchemy or follow some of the more basic preparations, and can use preparations based on their own Lores, but they cannot create new preparations.

The Dying Art

Alchemy is known as the Lore of the Material, the Lore of transmutation, and (among the more learned scholars) the Lore of Matter.
Alchemy is a dying Lore, because the secrets have not been passed on in over three hundred years. While many who can use Lore can perform basics of Alchemy and follow recipes and processes for certain preparations, unless they are truly an Alchemist, they cannot create new preparations.
Alchemy is one of the rarest Lores. Rarer than healing, but not as rare as Oracles.

Purposes and Methods

Alchemists are so powerful because their Lore allows them access to every sphere of Lore, at least to an extent. The use the physical to affect the physical, the magical, and the mundane. Some of their preparations can even effect Soul Magic, which is the province of Mind Magic.
Alchemy is simply put, the art of using mundane and magical materials to create new materials, preparations that affect and change other materials or enact magical effects on things, and transmutate one material into another.
Alchemists can create preparations that can do anything they want it to do. Their preparations can replicate any spell or magical effect known, and can do things no other Lore or magical art can do - with the notable exception of true conjuration.
The exact methodology is unknown, and the way materials interact with each other and what materials do what - how the preparations are made and why they work they way they do remains a mystery only known by Alchemists and their apprentices and are not shared outside their lineage.
Alchemy is fascinating, not just because an Alchemist can replicate any known magical effect or spell, but because they can create preparations they themselves cannot use, but those who are skilled in other Lores or High Magic can. They can even create preparations only muggles or squibs can use.
Thankfully, there are a great many tomes of knowledge concerning Alchemical preparations, meaning the knowledge we have of Alchemy now will not be lost, but the knowledge needed to create new preparations (outside of some very specific other Lores) will be lost within a few generations if new Alchemists are not trained.
The loss of a Great Lore would be a loss to the magical community of incalculable proportions. While it may someday be rediscovered, we are on the verge of losing an entire magic and magical tradition - and this can be laid at the feet of the short sighted and scared witches and wizards who imposed the Treaty of Versailles on Loremasters near the end of World War I.

The Shared Lore

While true Alchemists are very rare, Healer and Artificers are capable of rudimentary Alchemy and are known to be able to produce new preparations for their own Lores. While this does make them Alchemists of a sort, they are not Alchemists in that their understanding of Alchemy is limited, and thus their preparations are also limited

Unshareable Magics

Those without the skill and aptitude for Alchemy and without the ability to use Lore, a witch or wizard cannot use Alchemy.
Instead, they use potions. And while potions can replicate much of Alchemy, it cannot create new materials or transmutate anything.

Preparations

Preparation is a catch all term for anything an alchemist produces. Alchemists create powders, tinctures, salves, gels, liquids, potions, elixirs, sprays, materials such as metals and stone, plants, glues, paints and any other number of materials with both mundane and magical properties.
There is no true limit to what an Alchemist can create, outside of true conjuration, and with enough time and preparation, an Alchemist with a basic understanding of High Magic becomes a most formidable magician.
The two most famous Alchemical preparations are the infamous Philosopher's Stone, which allows one to turn any material into gold and to produce the Elixir of Life, which grants a sort of immortaility and agelessness - though, we are told it comes with a price, but what that price is has not been truly discussed or examined by any but the creator of the stone - Nicholas Flamel.

The Great Secret

The great secert of Alchemy is that it is one of the most versatile of all the magical arts, and is possibly one of the oldest Lores.
The original Alchemists were probably Healers and Artificers changing the nature of materials or creating preparations to heal. This is why there are tales of ancient craftsmen and healers who could do things with mixtures and combinations we cannot replicate - because we are not Alchemists.