The rules are essentially a (heavily) modified version of Art Magic, and frequently reference it without transcribing it, so I recommend you dig out your copy of the Magic Burner if you’re going to take a look.
I look forward to hearing remarks and feedback about the balance and story usefulness of these rules. Suggestions for additional modifiers and consequences are also appreciated.
I originally had detecting unobtrusive concoctions use Perception and be +1 Ob, but decided that would generally make supposedly subtle poisons too easy to spot.
As for the negative modifiers, one of my balance goals was to set it up so that stacking negative modifiers made the consequences of using them multiplicatively more problematic- the interaction between Horrible Taste and Large Product stands out to me, as does the potential interaction between Large Product, Horrible Taste, and Volatile (You started to drink the potion, then you started retching and drop it by mistake.) My hope is that interactions like these discourage alchemists from throwing on every negative modifier on the chart at a potion.
A cap on the number of extra dice from modifiers (lower of potion obstacle and Alchemy skill is what jumps to mind) would be a potential solution if balance issues came up during play, but I’d prefer to let it occur more organically then that.
Modifiers are there largely for flavor and gaining a few extra dice, though- my hope for the setup was to encourage the use of antecedents, rather then stacking piles of modifiers, to boost your dice pool for really big potions. That’s because the acquisition of antecdents can serve as a catalyst for stories.
It’s also worth noting from a balance perspective that refilling an Alchemy toolkit is an Ob 5 Resources test- churning out a lot of potions can get costly fast.