Can a magic user make a weapon for anyone to use? Specifically, a weapon that shrinks down to a pendant so that the non-magic person can carry it with them and call upon it at will.
To shrink a weapon would transform it from one size to another, so we must check "Transformation and Distruption" under Thaumaturgy [YS 282]. By the base description, it works via compelling "consequences" of the target. If we reference the basic rules on breaking things [YS 320] - "assume that an item has 2 stress boxes, modified by the item quality… most items do not suffer consequences" — if we can "take out" the item, we can assume that it has magically transformed from one form to another.
Let's assume that we had a Good(+3) Sword (4 stress boxes).
Enchanted item power:
This gives us Enchanted Item with +6 Effect.
So now we need a wizard to contribute his slots for this item who's able to place a +6 effect into 1-4 Enchanted Item slots [YS 287] giving us a size of "No smaller than Ring(ear or finger)".
How many slots will it cost an ordinary wizard? Great(+4) Lore wizard can pull this by exactly 4 Enchanted Item slots.
By default, this item can be used once a day to transform a ring-sized object into a Good Sword. If you want to use it more than one time a day, you have two routes:
The easiest way to handle this is to have an item at character creation (the permanent kind that takes up 2 slots of gear as oppose to the consumable that takes 1) with that as a sole effect. Unfortunately I can't think of any way to do this from what I've read of the rules other than to spend a Refresh to be the bearer of the object, and unless it is bought with the next Milestone it will be inexplicably gone by the next adventure.