Can specific magic armors be made from a special substance?

[asthyril]

For instance, can you have a suit of Mistmail be made by enchanting a mithril chain shirt instead of a masterwork chain shirt?

[Lab_Rat]

Nope. Named Items can not deviate from what is published.

From the FAQ:
"Magic armor and weapons may be upgraded to named versions if they are the same basic material and shape as, and meet but do not exceed the enhancement bonuses of the named versions."

[asthyril]

that is unfortunate. and imo an idiotic rule, they shouldn't have specialty armors at all if you cannot start with a better base material to make an item.

[Michael Brock]

As Lab Rat advised, it is already covered in the FAQ.