Less powerful artefacts are not made from a compound of a conventional material alloyed with a magical one but are a combination of the two with the magical material instilling it's power in the conventional one. Such 'conventional' artefacts follow my rules (for weapons) of a superior mundane item with a magical material bonus and powers according to it's artefact rating. Artefacts made from a solid magical material are much more rare though they were more common during the First Age, and far more powerful. With such artefacts anything seems possible.
   The scale of powers for an artefact made from a solid magical material are far greater than those made from a combination of a magical and a mortal substance. Use the characteristics in the end of Exalted for weapons and armour, but their individual powers dwarf these enhanced properties.
   Making these artefacts is considerably more difficult. They require far higher skill and a more sophisticated workshop. The ingredients they require are far more powerful and harder to obtain. Also magical materials themselves are rare and gathering enough to make an artefact entirely out of one is an impressive feat.
   Only the huge scale of Creation, abilities of the Celestial Exalted and the infrastructure they made allowed Wonders such as Warstriders (superior to Common Warstriders in the way pure artefacts are to common ones) to be made as anything by exclusive rarities.
   Noble Warstriders were so called because they were the first class of Warstriders to be made entirely from magical materials. Even then they were usually reserved for Celestial Exalted. Starmetal Noble Warstriders were unheard of.
    In lesser artefacts the magical material may be a piece of carefully cut jade in the guard of pommel of a sword or a talisman in a suit of armour. A hearthstone amulet should be just that, an amulet with special powers like Tullaris' Black Amulet. Only the most basic ones would just house a hearthstone and slightly increase the rate of Essence recovery.
   The description of making the Fellblade in the Skaven army book is a good example of artefact construction.

    Only solid material artefacts can contain the energy that the creation powers of a greater magical ingredient gives. No one would waste precious magical material on making a solid artefact just to use the powers of lesser esoteric ingredients. It's the ingredients themselves that give the artefact it's unique powers. The magical material can contain their energy and provide a bonus.