Clay belongs to the "lower tier" of Terram, in the sense that a Base Individual of Clay is as large as a Base Individual of dirt, and requires no additional magnitudes to be affected (unlike what happens with stone or metal).
What it's not entirely clear to me is whether this includes just "wet", "natural" clay, or fired/baked clay such as brick or pottery too. Part of the reason is that my understanding of the material and its processing is quite limited! Could anyone enlighten me? Bonus points for evidence in supplements!
EDIT: apparently this first post wasn't clear. I rephrased the question in a post below, that's hopefully clearer:
Well in Covenants there is a spell that is similar to what you are talking about. Its the Spell of Wrought Iron and it transforms raw pig iron into plain bars of wrought iron; it is ReTe 15; Base 2, +2 Metal, +1 Touch, +2 Group
The thing I notice about this is that it uses the Base 2, control dirt in a slightly unnatural fashion, with a magnitude boost to make it metal, but no magnitude boost to make it something different.
Which means I figure that a similar spell could be created to transform natural 'wet' clay into worked fire/baked clay without having to add a magnitude to things.
OR if you truly do feel that there needs to be some complexity involved than I can see using the idea of the Phantom Blacksmith on the same page. This spell transforms iron bars into crafted and formed results. (It is ReTe 20; Base 2, +2 Metal, +1 Touch, +2 Group, +1 flexibility)
I could see a ReTe spell to take raw clay and make it into workable buildable material with a spell like this designed as ReTe 10; Base 2, +1 Touch, +2 Group, +1 Flexibility.
Both ideas are Covenants page 51.
I looked things up in the City and Guild book but they didn't have any particular rules on pottery and stuff like that.
I think it's reasonable, when working with muto to allow the change along the same category to be for free. After all, the guideline is change dirt to another kind of natural earth. IF we apply the +2 metal magnitude increase, we could read it as Change base metal to another type of base metal. Making the magnitudes add twice for the material changed from AND the material changed makes Muto an even weaker Art.
Ezzelino, seem to recall seeing Aq requisite requirements somewhere for clay, but I'm not able to access my books just now.
Right. I can understand the annoyance of that requirement (and my dislike of such a finesse roll notwithstanding). But at least its a permanent change when using Rego rather than a temporary one when using Muto. It is also what the books use when they have permanent spells that take raw and make worked materials out of it.
Maybe I wasn't clear. What I was asking is this.
If I move a metal brick around through Rego Terram, I add +2 magnitudes on top of everything else because it's metal.
If I move a stone brick around through Rego Terram, I add +1 magnitude because it's stone.
If I move a brick of wet river clay around through Rego Terram, I need not add any magnitudes because clay is in the same "basic tier" as dirt.
What if I move a "standard" brick -- you know, the reddish ones you build walls with (which I believe are made by baking clay in an oven). Do I add +1 magnitude for something like stone, or do I keep the cheaper guideline for unbaked clay?
Well, it was understood, to the medieval mind that a fired piece of clay was different from wet clay, and it was like stone. IMO the change to stone should hold for Hermetic Magic, and fired clay needs the +1 magnitude for stone. I don't have a canonical example of treating fired clay this way, though.
Fired clay objects certainly seem stone-like. They are rigid, unlike sand/dirt/mud/wet base clay, which are relatively fluid.
Using fluidity is problematic, though, as it implies that a sufficiently large number of small stones (gravel) should be treated as a base earth material. It also implies that molten rock is a base earth material.
I suppose there's a barley corn test involved. A Terram object larger than a [something] at ordinary temperature is a stone, not a grain of sand. It may indeed be a barley corn.
From what I'm reading, clay -- even when not fired -- is not necessarily plastic (i.e. non-rigid). If it's dry, as it's sometimes/often found in nature, it's firm. Again, let me say that my expertise on the subject is virtually zero.
I wouldn't require the spell to be a higher magnitude because the clay is fired. In the terram guidelines, clay is explicitly between earth (sand, dirt, mud) and stone. The Rego Terram guidelines explicitly state that clay is included in the base guidelines. Degrees of hardness is pretty far down the Aristotelian list of properties of the form, are bricks something that falls under the form of clay or not?
I agree. Actually, I don't understand why stone should be harder to Rego than clay and precious stone harder than stone. For Creo it makes sense, but moving a rock, brick, and diamond all seem about the same to me.
Well, that's the question.
On the one hand, it can still be called clay -- fired clay, that is, i.e. ceramic.
On the other hand, if you fire it, clay becomes something qualitatively different.
In some sense, that's the case of glass too -- it's melted sand. But glass and sand are in two different categories.
While the text does not say, note that glass has exactly the same "magnitude modifiers" as stone for all Forms... so I'd say it's the same as stone, one cubic pace. It's certainly no more than stone, given that glass is technically higher than stone in the "difficulty to affect" hierarchy.
The simple way to subdivide this is by the level of focus.
A Major Focus in Clay would cover brick and pottery as well as naturally sourced clay.
A Minor Focus in Clay would cover unprocessed wet/dry clay.
A Minor Focus in Pottery would cover pottery as well as the making of pottery from natural clay.
A Minor Focus in Brick would cover clay brick as well as stone bricks.
The same logic applies to sand and glass:
A Major Focus in Sand covers granular sand, glass and sandstone.
A Minor Focus in Sand covers granular sand - strong in the desert or on the beach, otherwise somewhat weak.
A Minor Focus in Glass covers glass and glass-making from sand.
Someone with Major Focus in Soils could affect sand, loam, clay, peat and similar, but none of the processed results of such.
No, the question here was simply if fired clay (so bricks, pottery etc.) should be treated as stone, or as "plain" clay for Terram guideline purposes (i.e. the Base size of Individual, and the magnitude modifiers to affect it with Rego, Muto etc.).
Apparently the opinion is somewhat divided; and no one has come up with canonical examples resolving this. Personally, I'm starting to lean towards "stone/glass", given a) the analogy of "clay vs. fired clay" with "sand vs. glass" and b) the fact in my saga, fired clay would see disproportionate use if it counted as dirt rather than stone (whereas if it were ranked with stone, it would still get used but not as much). But I could still be easily swayed either way.
I can see glass going either way, but I prefer stone. A giant glass block is hard, durable, etc.
I would not apply modern criteria, which would also have glass be stone (since some stones really are glass.)
The great thing about glass is that you can make the stuff with sand or dirt, ReTe and nothing else, though it won't be tranparent. Magi in glass houses can throw stones, if the glass is 10 or 20 feet thick!