LOL, yes in truth Xavi, but what Brutus should have said (concerning his particular example) is not changing between elements but between magnitudes of AN element, as mentioned in the MuTe guidelines...
Does that apply to Muto-ing BETWEEN elements or substances as well?
Xavi
Thats a good question. Of course, the MuTe guidelines only speak about dirt, clay, stone, metal and gemstone (changing to and from) as either the starting or end state.
I can't think of any reason why it shouldnt pertain to changing other substances into a Te form or a Te form into other substances, but since "cubic pace, foot and inch" are Terram Form "individual" base sizes I suspect you would have to check the individual base sizes for whatever other Form you wanted to change to or from Te and extrapolate on that basis.
Phlogiston theory wasn't formulated until 1667, so I would say that the necessity of air for combustion was not clearly understood in the Ars Magica era.
I don´t know but is the Rain of Oil Spell still around ?
In the older Editions they had a Spell that made it Rain Oil (IIRC it worked only outdoors).
It just drenched everything with Oil you had to apply the Flame yourself.
Maybe using it as a frame you can work something out ?
Oh and thinking about it how about Gas ? I think naturally ocuring Gas is known, at least to Miners........
Just add a Flambeau.
So if I find a dinosaur bone, am I immune to demons? 
Sure, if you want to think that 
. However, the dragon whose ancestor you just dug up might be a tad upset. Remember, dinosaurs don't exist in the MP, but dragons most certainly do. 
Steve
More likely you just have a poor animal score and you found a cow bone
Animal Lore...ahem.
..but your right...my animal score is a bit low...gotta work on that..right after I take over the Order... 
thats a different thread..
The Phlogiston theory was a bit of a step backwards from the Aristotlean tradition. I think Bacon, Aquinas, and other scholars of the day would have found Phlogiston laughable.
Anyone whose hovel had a fireplace would have understood the importance of air for a good fire, though they might not have understood the chemistry of combustion as we know it today.
Actually I would think that a simple to visit to any blacksmith or foundry (considerably further back in time than even the Ars era) would provide ample understanding as to the importance of air for combustion.
Any Verditius by 1220 would certainly know the value of a bellows after all.