The Elven magic was that of Creation. It fundamentally allowed them to replicate the atomic structure of things as they saw fit.
However, for this to happen, one also needed extensive knowledge on the item that they wanted to replicate. This included its structure, Chemical properties, Physical properties and how it reacts with other elements.
Of course, things only got more complicated if it was a compound and not just an element, as how they chemically combined was a factor to note.
The details and formation of an item even got deeper if it is inscribed with runes, as runes have the potential to fundamentally change the foundations of a particular substance. Of course, this went into even deeper details depending on the kind of runes.
For example, a soul rune can turn an ordinary mirror into a parallel world and therefore change its fundamental composition or function.
