The Materials table on p.97 of the corebook lists the "base points" for a large set of materials that can be enchanted. However, I noticed that quite a few possible enchanted items would be made of materials that are not part of the table.
What about a clay jug? It's neither glass nor stone (the Terram guidelines treat it differently, among other things).
What about a straw hat? It's neither wood nor cloth.
What about bread or wine (or, as a matter of fact, any liquid such as blood)? These are often great for charged devices.
What about the ghostly sword of a ghost?
The problem is that some of the unlisted materials are listed in later supplements as providing shape and material bonuses, so they can be enchanted. However, without a base point listing one cannot determine the total vis capacity of items incorporating them. Any ideas or pointers to "official" rulings?
It's not hard to interpolate these, is it?
Straw is no better than cloth.
Clay isn't really any better than glass, is it?
Use the listed values on p.97 to estimate the others. Just because it's not on the list doesn't mean it can't be enchanted, and something need not provide a Shape or Material Bonus for it to be enchanted.
- Clay jug: Looking at clay listed alongside sand and mud with the Terram, I feel "clay" is not what you're thinking. You want fired clay, whether you call that ceramic/earthenware or something similar. I'd put ceramic closer to glass, as in (drastically oversimplified) sand+hot=glass and clay+hot=ceramic/earthenware. Similarly, clay+hot=brick and brick is similar to soft stone. Overall I would probably place ceramics/earthenware at 2, somewhere between glass and soft stone. A jug is reasonably close to the size of a skull, so I'd put it at 2x3=6.
- Straw hat: I would tend to consider using straw to make a hat similar to using cloth to make a tunic. As long as it's not a really big hat I'd put it at 1x2=2.
- Bread or wine: Generally softer materials are lower in base points, so I would put these at 1, though I would probably refine the latter by putting water at 1 and raising wine to 2 because it's a more precious water in some ways. Blood could then be raised even further above wine. Perhaps animal blood is 3 and human blood is 4? Then figure out how large the bread or wine (or blood) is.
- Ghostly sword: I expect for things like this you'd have to consider it's material equivalent. Go with a metal sword, typically 5x3=15. There could be other problems working with it, though.
Finally, the most important step is to come to an agreement within the troupe. If you're agreed, perfect. Then record the decisions so you remember what you all found reasonable.
Generally, the harder a material is to aquire - the more rare it is - the more Vis can it hold.
I assume you mean burned/fired clay?
The one time it came up, I think we ruled in 'soft stone' though I really prefer the suggestion above to take an average of glass and stone
Cloth in my book
Why? Charged items require no vis and as I understand can simply just ignore Material and Size elements.
Off hand, why would you enchant something like this with a lasting effect? Would the risk of someone drinking the wine or throwing it away not be too much to invest Vis in it? I'd invest the container instead.
That said, what's the Vis capacity for human flesh? We had this come up, with a magus that wanted to enchant a corpse to not rot (among other things). He ended up investing the bones instead, but...
Ah, now that I normally wouldn't allow you to enchant without some serious tricks.
Technically, that sort is part of the ghost itself.
Perhaps with a Mental construct lab?
That said, I'd go with base metal, because it "mirrors" a steel/iron/bronze blade, which would be base metal.