Expanding the basic Material and Size table

He everyone,
Has anyone used any extra types of materials for making magic items? I am not talking about S&M bonuses, but the actual calculation of how much vis it can hold. Could there be bonuses or penalties for using materials associated with different realms.

I travel to the magic realm and come back with some iron forged by a mythical creature. This is "perfect" iron, better in every way than any mundane iron. Can it hold more vis?
I use "The Touch of Midas" ritual to create some "Perfect" gold, does it only hold the standard 10 pawns of vis, or can it hold more?

I know that various virtues allow you to cram more power into a material, but I am talking about things available to every magus.

Has anyone used anything really exotic, that they had to quest to the furthest parts of Iberia for?

Or anything suitably mythic - meteoric iron, faerie worked silver, thigh bone of a dragon?

It's never come up in our current saga where magi tend to enchant either talismans, or lesser enchanted devices; but I remember that in a previous saga I was in we had this simple house rule: if a material "naturally" contains vis, that vis counts as "extra slots" on the device. So a perfect, priceless ruby, that would normally be opened with 20 pawns, if naturally containing 8 pawns of Ignem vis could be opened with up to 28 pawns of vis, and hold up to 280 levels of enchantment.

That is a good idea, and it stops everyone from draining the vis out of whatever it originally came in.

This is the reason we have odd bits of animal and objects in our vis store. All those people who insist on draining it away into a "standard" container are missing out!

I also remembered that we have other things, for example Alchemical Steel?
How about using purification on some stone (as if to create an elemental)? It gets enchanted before it awakens as an elemental.