Transmutation Branch

Science has figured out how to shape matter to some degree. But substance is a matter of perspective and will as much as it is an objective fact. Through complex processes, led can actually be turned into gold, steel can become unbreakable, and flesh can become stone. That is only the beginning of alchemy for those who can get more creative with it.
The Branch of Alchemy shouldn't be confused with the traditions of Alchemy. The latter is a method that can channel any Branch or not do anything at all if the person isn't initiated. Somewhat confusingly, alchemy can be used for the Alchemy Branch.

E=mc²

Energy and matter are the same. Alchemy users knew this fact centuries before Einstein proved it with modern physics. They also know that the power it takes to pull on a Branch is another form of energy. Done right, this means that any magical energy can be turned into a thing or change it. Making lead to gold means releasing the energy in one metal and using it to form the other.
Many uses for this power includes either working with large amounts of matter. For instance, some pull on this Branch to turn useless objects into valuable materials in order to make money. The danger is that the more material affected, the higher the risk of Thorns ripping at the user. In fact, Thorns might hide inside the creation itself. More than one magic-user has found themselves having their friends die from the monsters coming from their fancy new gear.

Thorns

Pulling on any Branch means a risk of being injured by the Thorns. For Alchemy this often means uncontrolled releases or absorption of energy. A potion might result in a firestorm that engulfs everything nearby. A hardened metal might freeze and cover everything in thick ice. There is a reason for the archetypical explosion in an alchemist lab.
There are some examples where the Thorns have cut the user up and turned their body inside out. Sometimes without killing them, only causing excruciating pain. In at least one case, a potion resulted in the practitioner melting and becoming a sentient goo unable to do anything but feel themselves thinning out.

Manifestation

Any use of alchemy depends on the change in matter or energy, which is often accompanied by flashes or sudden darkness as light is emitted or absorbed to feed the process. Instead, there might be heat, byproducts, or the destruction of nearby things. You can't get something from nothing and you can never completely destroy anything. Balance is always maintained, no matter what you do.

Common Traditions
Alchemy

Type

Metaphysical, Arcane