I don't get the Archaic Alchemist from Geomancer's Handbook...
Does it replace Alchemy (extracts..) with normal Sphere Casting, losing all the "alchemist" flavor (extracts, again...) ?
And I can't understand the casting tradition...
Focus Casting drawback is "alchemy lab", so... alchemist can only cast with an alchemy lab in front of him ? What's the point ?
Only logical explanation could be that Skilled Casting drawback (craft alchemy) is that you use a sphere ability in front of an alchemist lab in order to imbue a potion with power but... it's not written...
So, please, explain it to me :)
The Archaic Alchemist replaces the Alchemy ability (which includes Extracts) with Spherecasting, yes. Basically, the idea is that you're mixing stuff together to create your alchemic effects (Skilled Casting), and this is much easier if you have a proper lab to do it in - or at least a portable version. That's a 75 GP, 20-pound item. If you don't have the lab to work with, you can make a Concentration check instead.
The actual effects can be whatever spherecasting allows, though most people will want to flavor it alchemy-style. For example, if they're using the Dark sphere, maybe they're mixing up a strange alchemical substance that sucks up light in an area. Flavor and mechanics are broadly separate in Spheres of Power, so you can easily adapt your ideas.
Thanks I get it, in fact the flavor is great, the alchemist is doing alchemy while in combat and not just throwing extracts !
So the portable alchemist lab could be an apron with a lot of pockets on the front, with a lot of alchemist stuff in it.. and the alchemist mixes things, shakes things up, and boom :D
Pretty much, yeah. ^^ There's plenty of other ways to flavor it, of course - what's important is having fun with it. XD
You may also want to look into getting the Alchemy martial sphere somehow (loads more options there) and some additional drawbacks to further cement the theme. The Medicinal drawback for the Life sphere is particularly appropriate (you make drinkable items that can heal people), while the Energy Focus drawback for the Destruction sphere can represent only having the chemicals to make one 'type' of effect there.
That's a 75 GP, 20-pound item. If you don't have the lab to work with, you can make a Concentration check instead.
It should be emphasized that the Focus Casting drawback does not specify anything about the cost, weight, or size of the item, just that it can be taken away. I assume saying "alchemist's lab" is flavor text and not requiring the use of that specific item.