The constituents of common green bottle glass are 200 lbs. of wood-ashes and 100 lbs. of sand
ReTe craft magic can process something from one form to another, so long as a normal craftsman could do so and all the raw materials are available (unless Creo magic is employed).
So what would be the magnitude of this spell? I'm thinking:
Speeding the Glazier's Craft (ReTe 5)
Turns constituent materials in glass, of a quality and type depending on the materials and the Finesse roll. The glass appears as a flat sheet with dimensions specified at the time of casting.
[Base 2 (Control dirt in slightly unnatural fashion) +2 for Voice, +0 for Momentary, +0 Individual, +1 for glass]
You could event add a +1 magnitude for elaborate effect to be able to shape the resulting glass into a useful form. But that might involve 2 Finesse rolls, or a higher one. I'm not certain.
I think I would add the +1 for elaborate effect, with this spell you can probably make glass sheets with a larger surface than is yet possible.
Either that or even better add an Ignem requisite, since a lot of heat is required to create glass.
But according to the Rego Terram Guidelines, sand, dirt, mud, or clay are equivalent. And only one magnitude need be added for stone or glass (which are equivalent to each other).
However, I could see an argument for stating that this is Base 3 (Control dirt in very unnatural fashion) rather than Base 2 (slightly unnatural). And then adding the +1 magnitude for glass.
As for Ignem, I believe the discussion of Covenant crafting magic states that intermediary treatments (e.g. soaking or heating) do not require requisites or materials so long as they are not present in the final product. So, as the glass itself is not hot when the spell is finished, I would think that Ignem would not be required.
But I wonder if Herbam would be needed as wood-ash is one of the materials. Probably this would be a Casting requisite is anything, as the materials used for the glass may change.
I would suggest that your quote is out of context. Because the surrounding text states that most glass of the period is colored and has bubbles in it. And I believe it explicitly states that this is the type of glass object that results from the craft spell I described first.
I'm satisfied with making glass that is imperfect. I don't need to make clear glass. So is your statement that manufacturing glass of any type, clear or not, is beyond a craft spell?
Animal skins can be chemically treated to tan them using Rego craft magic and raw materials. So why is creating glass any different than producing tanned animal pelts?
What is the definition of an alchemical process and what is needed to emulate it? Additional magnitudes or different magic?
If I remember correctly the wood ash isn't essential. It's used to lower the melting point of the Si which normally melts ~1400C. Since we're dealing with magic that temperature is obtainable. As is breifly noted in the link you provide the additives effect the final properties of the glass.
So YES you can just get some sand and melt it into shape BUT I'd say the final quality will be lacking comparable to a trained glass maker, unless you've also studied glass working.
Nope, he was just pointing out that the glass is not clear glass as the one that we have nowadays. In case you missed it. no more no less A worthwile comment since at least I didn't recall it!
The proces is alchemical, not only chemical. Alchemical stands for quasi-magical, so no simple rego will do it. You mneed some sort of supernatural effect to create transparent glass in mythic europe. So yes, it differs from simple tanning, that is a chemical process, quite different from an ALchemical process
I think we have no guidelines for alchemical processes, but extra requisites and magnitudes should do the trick. probably a creo requisite in order to cope with the extra perfection that the glass is aquiring. An unnatural change for sure in any case. Hope that helped .
EDIT: @Angnar: doesn't the extra difficulty of craft rego spells account for the lack of skill? I thought so, but I have not used that zsection of Covenants ever (even if I like the concept), so I might be mistaken.
You could also make the glass transparent using Muto , but this would need to be sustained , unlike Creo.
In this case you can have "privacy glass".
It is transparent , but only from one side.
You can see out through your window , but those on the outside cannot see in.
Ravenscroft - I must be thick-headed today because your statement leads me to surmise the opposite (Rego Craft magic could make Clear Glass). If you're willing to continue to help me, I appreciate it.
I agree the text states Clear Glass as being outside the purview of Rego Craft magic. I'm going to put that aside for the moment, and just concentrate on trying to identify where (if at all) we disagree in the absence of that statement.
I agree Rego cannot create matter. This is the purview of Creo magic.
I posit that Rego Craft magic is capable of processing raw materials into a new form. E.g. You can tan animal hides, which chemically alters them, so long as the raw materials are available. Or you can turn raw ore into a finished ingot, which requires purifying it and re-shaping it.
Therefore I posit that Rego Craft magic could process raw sand and a few other elements into inferior glass (e.g. cloudy, colored, bubbles).
If you accept this, that Rego Craft magic can create inferior glass, than it seems by your own statement that you accept a further application of Rego magic (and a high Finesse roll) could render it into clear glass.
The high Finesse roll merely removes air bubbles and distortions in the glass.
It does not make the glass clear by doing so.
You could also use Rego Craft to polish any finished glass to a high sheen.
Again , this wont make the glass clear , but it will reduce opaqueness.
If it were not for the comment about clear glass in the spell ,
i would have assumed that you could make colourless glass as per the write-up in the link you posted.
If you end up having to make Clear Glass using Creo (should you need to do so) ,
i would make quartz instead.
It is naturally clear (impurities give it colour) and it is harder than glass.
It is also the same magnitude of effect as stone and glass spellwise.
A momentary Creo ritual using Vis will make clear glass.
Muto effects to do so , as reminded , need to be sustained.
Also, I agree that adding a Creo requisite (not casting, but as part of the spell's design) would seem sufficient to "perfect" the glass into clarity. Note that I distinguish between "clear" (e.g. transparent) and colorless (e.g. without hue, shade, pigment).
I think the color of the glass would be largely dependent on the raw materials and so color or colorlessness might be achievable by Rego magic alone in my opinion (though some of the materials for clear glass could be esoteric enough to fall into an "alchemical" classification).
I read the "cannot manufacture clear glass" as being a statement that the glass is naturally cloudy and therefore only translucent, no truly transparent. That's why I didn't understand your point.
With your clarification, I agree that you could remove bubbles and distortions with Rego and a Finesse roll. But the glass would remain cloudy (e.g. only translucent) unless non-Rego Craft magic was employed.
And I agree about the advantages of quartz if magically created.
Unlike others with more actual play experience with Ars Magica ,
i have to make quite a few guesstimates most of the time. Fabricate in DnD , is a spell i am more used to.
(or abusing as a player for my DM)
No amount of mundane craft can produce clear glass: alchemy is magic. Even with high finesse rolls, ReTe will hit an absolute limit - your glass will still be imperfect. If you want clear glass, find a mythic glassblower (IIRC the example glassblower in the NPC section of the book is stated to have dwarf blood and be able to produce such clear glass), or use CrTe rituals.