Definitions:
ceil(x) will round up to the nearest integer. Also called the least value function. min(x,y) will return the lower value of the two. max(x,y) will return the higher value of the two. A combination of these and parentheses can be used to calculate all values. skillLevel: the TOTAL skill level over all the pots (ie. an AL 50 and LF 60 pot has a skillLevel of 110) duration: self explanatory
Below I've compiled a list of all of the composing formulas available to the community/released by hoof. Enjoy.
Experience:
experience =(ceil(min(skillLevel,duration)/60 + skillLevel/500)*10)
Gold Cost Per Potion:
goldCost = max(skillLevel*duration, 5000)
Time to Create Potion:
timeToCreate = (max( ((ceil(max(skillLevel,150.0)/20)*5) + (ceil(duration/30)*30)) - ((composingLevel-1)*5), 60))
Cost to Create Instantly:
instantCost = ceil((1 - (percentComplete / 100)) * initialGoldCost * (2 ^ instantCompletesInLast24Hours))
Also, in case anyone is wondering, here is the best possible achievable XP per minute (roughly). The values are based on the approximation that the maximum possible skill level in a potion goes up by 150 per level, which may or may not be true as the levels progress.