An arcana focus is a piece of rune-inscribed metal, stone, wood, or cloth which, when attached to an object, gives an arcanist the ability to manipulate that object remotely via their arcana skills.
Mechanics & Inner Workings
The color of the arcana focus's decorative inking and the specific runes inscribed upon it determines the specific ways in which an arcana user can manipulate the object to which it is affixed. For example, a green arcana focus might be affixed to to a Clockwork Automaton summoned from the Winder's Guild's stock, allowing the summoner to directly control the pre-programmed movements and functions of that automaton without having to know how to build, program, or otherwise manipulate said automaton's machinery directly. In another example, a blue arcana focus inscribed with one set of runes might allow an arcanist to see the environs of the focus remotely, in the manner of a crystal ball, but another set might instead allow the arcana focus to conjure a bank of illusory fog; the key, in this case, is that blue corresponds to powers of perception, while different runes might correspond to the enhancement or ablation of perception.
Arcana focii are common sites in the workshops of arcanists, alchemists, and clockwork engineers alike. Because they require specialized skill to manufacture and employ, however, most of the public has only passing familiarity with the objects.
1' to 12' diameter
Raw materials & Components
Arcana focii of any material must first be shaped into circles or spheres, with the shape determined by the way in which it will be affixed to the object to be affected by it. The focii must then be inscribed with specific magical runes, which are then inlaid with inks containing the powder of various appropriately-colored precious stones.