I assumed this would be a fairly manageable spell, but thus far, it seems quite tough.
The goblin-tainted Merinita magus has found a spider in a certain tomb in what used to be Garamantia, and has decided to bind the spider as his familiar.
He knows it is exceptionally frail, and so wants to protect it.
Hiding inside the Mage's beard, and turning that beard into steel was an idea.
The Steel Beard
[Base: Turn individual into an inanimate object: 25 - ow.
Duration: Sun +2
I was thinking this would need to be Target: Part, for a +1.
That makes it a level 40.
This seems pretty extreme.
Is there some other way to get this effect than using the Base 25?
If he unlocks the Glamour mystery he could use the base 10 Muto Imaginem guideline...
Edit: Alternately, you might appropriate the Muto Animal 15 guideline to change a Corpus target in a major unnatural way.
It doesn't have to be actual steel, the beard just needs to be hard as steel (see the MuAn spell Doublet of Impenetrable Silk). So you're just adding a "hardness" property to the beard.
The target is Part, though, not Individual.
I don't have my books with me, so I can't quote you a base level.
Base 5: Change something made of animal products in a major unnatural way. Change an animal in a minor way so that it is no longer natural (for ex change the color of a horse so that it matches the covenant's coat of arms).
Base 10 "Change an animal into a plant (He requisite)"
Base 15 "Change an animal in a major unnatural way (for example, give a horse claws, fangs and sclary armoured skin)"
I would use those over the MuCo spells. The MuCo gidelines are biassed, as to prevent you making your skin as tough as adamantine easily (+1 soak for base 5...), and they do not provide the same level of flexibility.
Your plan B would be making the spider totally unnatural (tough as stone) for Sun duration. Level 25. I like Mark's idea of giving your beard an extra "toughness" property. Thart spell does not feel like level 40 at all, that is for sure. Around here the "feeling" is still important
Doublet of Impenetrable Silk uses a MuAn Base 4: change something made of animal products in a minor unnatural way. This is actually easier than changing a living animal in a minor unnatural way, which is Base 5, and so you would have MuCo 5 : change a human in a minor unnatural way.
You could make a case for using the MuCo Base 2: Change someone to give them a minor ability. If it works for Eyes of the Cat, why couldn't it turn your beard into a hedgehog's spines ? Not steel, but cheap: Base 2, +2 Sun, +1 Part (you don't want to turn all you hairs into hedgehog spines, just the beard !), animal requisite is free, total level 5. That should give the spider at least some protection.
Or by analogy with MuAn, you would have the MuCo Base 5: change a human in a minor unnatural way (harden the beard). You'll have to negotiate with your ST for the actual, mechanical effect. I would say you do not need a Part requisite (minor unnatural way can cover just the beard), so Base 5, +2 Sun, total level 15. Add a magnitude for major unnatural way and more protection.
For that matter, if Eye of the Cat use a Base 2 when turning a human into a cat is a base 10, then you can also argue that turning the beard (only) into steel should be 4 magnitudes easier than turning the whole human into steel: so Base 5 since turning a human into an immaterial object is base 25. Which fits well with the guideline calculated previously by analogy with MuAn.
I would agree that the right guideline is the Level 2 "Change someone to give them a minor ability" (like Eyes of the Cat). R: Self, D: Sun, T:Ind yields a level 4 spell that a magus can cast spontaneously - and even without fatigue with a decent MuCo total.