create magic items, spellcasters use special feats which allow them to
invest time and money in an item's creation. At the end of this
process, the spellcaster must make a single skill check (usually
Spellcraft, but sometimes another skill) to finish the item. If an
item type has multiple possible skills, you choose which skill to make
the check with. The DC to create a magic item is 5 + the caster level
for the item. Failing this check means that the item does not function
and the materials and time are wasted. Failing this check by 5 or more
results in a cursed item (see Cursed Items for more information).
Note that all items have prerequisites in their descriptions. These
prerequisites must be met for the item to be created. Most of the
time, they take the form of spells that must be known by the item's
creator (although access through another magic item or spellcaster is
allowed). The DC to create a magic item increases by +5 for each
prerequisite the caster does not meet. The only exception to this is
the requisite item creation feat, which is mandatory. In addition,
you cannot create potions, spell-trigger, or spell-completion magic
items without meeting their spell prerequisites.
You can use spellcraft or craft(alchemy) for the final check to create the potion/oil, but the brew potion feat is still required.