Someone said Calebais?
Xavi
I work from a very limited set of source books. At the moment, Covenants and the Core book, although I have gotten to skim a friend's copy of HoH:MC, and, of course, a few others in the local gaming store 
. It is an interesting phenomenon, as I acquire more books and have house rules replaced by Canon. My labratory customization rules were much more straight forward 8). City & Guilds might have some extra info on this particular topic (about mining at least), I don't know. Anyway, point being, I haven't read the Calebais supplement.
Re: Gilarius
That's very interesting stuff. I'm still reading the cited dissertation. It has some interesting background on bronze age mining techniques.
The problem with that statement is that making magic real, means that you simply cant use current historical knowledge to set limits, because a lot of those limits will very likely have been shifted by the availability of magic to try things otherwise not possible, or at least very hard, for many centuries. As it IS magic, and magic is an art not a science, you wont get as absolute answers, but there will be pointers and hints of many things most likely around.
Also to note, we dont KNOW all the things ancient philosophers did consider simply because our knowledge of that is very incomplete.
In short, "anachronistic" becomes almost impossible to truly define.
Stone does NOT compact easily or "willingly". Do you have any idea what kind of pressure you´re talking about to achieve it?
You´re in the range beyond "solid surface of Jupiter" where the pressure is extreme enough to turn gasses into solids.
If you want to compact stone like that, i suggest you add a Muto requisite. The stone will be superheavy, superdense and extremely strong after the treatment. Nothing but magic will make a dent in it.
:mrgreen:
Who cares about "22nd c outlook"? I´ve played with real world physics as the basics ever since the 2nd game running using 2 edition rules, because players would twist the fake physics into a pretzel, do a song and dance show of munchkinism and come back with level 10 spells that could destroy the universe as a sideeffect.
Ooops...
Hmm, i get the feeling you´re mixing things up here. More stable, of course it is. FAR more unnatural than carving it into pieces though. And there´s a huge difference between "CAN be compressed" and how realistic it is actually doing so.
Different types of stone has different "ingredients", NOT different degrees of compression. Higher atomic density does not equate a higher degree of compression.
Sun duration would probably be enough as clay can be worked rather quickly.
You could have the spell separate different sorts of materials from each other, or you could have the spell mix them up equally all over which makes the question a moot point.
You do. If you want to make it harder, increase the difficulty for getting a perfect result but again, it´s your call.
And GIlarius already went over the stuff about mining...
Rego magic doesn't worry about that. It transforms it's target from one natural state to another natural state magically without needing to copy the process. Fr'Instance, if (big if IMO) slate in Mythic Europe is actually shale transformed by a purely natural process, and if (also big) Magi know this and if (least likely if by far) slate isn't inherently better or worse then shale, then rego could be used to change it's state. The magic doesn't copy the natural process it circumvents it.
Their is no solid surface of Jupiter though it might have a solid core. As you go down the pressure gets high enough that the gasses become liquid, but pressure alone can't make most gasses "solid". Even then your talking pressures far in excess of what is achieved in the earths crust when metamorphic rock is formed. But that's neither here nor there for Mythic Europe.
Reason for edit:Re-Enabled spell check.
And where do you think the "solid surface" is then? Oh yeah, at the edge of the solid core perhaps?
That is under debate. And it´s what´s postulated as giving Jupiter a solid core anyway.
Dont you notice the contradiction you set up between those?
A neutron star is 100% natural.
You´re saying both that any potential natural state is just fine by Rego alone, as well as that it might not be, but without setting the limit.
The original spell leaves the degree of compression completely openended and already suggests compression that isnt remotely possible on earth.
Yes i know. But that was never the problem. About the most extreme compression you can get is carbon to diamond. Do you know the degree involved? Density goes up to around not quite double.
NORMAL density changes for stone is just a tiny fraction of that. The original spell would have gone potentially way beyond.
Getting carbon compacted into diamond takes extreme pressure and heat over time, and yet you say that it´s just fine to allow compressing stone together far more still without even considering it unrealistic?
This is where we come back to the "fun stuff" of spells that can wreck the world despite being lower level than a standard PoF.
What is the type of Daimons in charge of those stars?
Xavi
My evil self can't refrain from saying it didn't help for "it's" or "their". 
I am not confortable with using Rego to transform some stone into another one, even if it can happen naturally. OTOH, water to ice/steam doesn't look that bad.
I have to agree with that. There's a big difference between air, water and earth at low temperature/pressure. I don't think there's much of a contrast between those when it comes to Jupiter. The phase change is more a continuum than a break.
Jupiter's surface is usually considered to be when the pressure gets to be around 10x sea level on earth. Apparently at that point while still gaseous the substance of the planet stops acting like an atmosphere.
Greetings all, long term lurker here decided to register because I just can't resist temptation to commen myself.
Now, regarding the issue of items at hand...
First, I'm sorry but you are wrong about mining. Ancient romans rather regularily dug mineshafts and had lots of rather innovative ideas for mining.
One method was to make shafts which opened up to a cliffside, then direct dammed water into shafts to tear up material from the walls with pressure to gather materials at the bottom of the cliff.
They also used traditional mine shafts even below aquified. Romans made series of waterwheels which would each lift the water one level upwards in the mine unti it could be discarded out of the mine. Work intensive methods, but slaves were plentiful.
On another issue, regarding necessity of profession in crafting magic...
Using the example with Ex Miscallanea and Jerbiton...
I would say that both would be able to make a functional tower, as rules say. But having professional skill would, in my opinion, make it bit "better". Functional tower has stairs, but one which is made by architect have all stairs narrow and rotate clockwise for defensive purposes. This because most people are right handed and it is more difficult to wield a sword which is on inner curve of the stairs. There would be uneven stairs which would make attacker unaccustomed to way stairs were made in that castle stumble in poorly lit conditions. And perhaps holes from which spears could be thrust at climbing enemy.
So, both make functional buildings which fulfill their purpose, but one can have some extra attributes in it that makes it bit better without affecting the basic functionality.