The potions described here are mixtures made from harvested parts of creatures. They typically come in either potions (which are drunk) or oils (which are spread over a weapon or flesh), usually with a dosage of 1oz.
Potions and oils are made by mixing ingredients gathered from the world around the crafter. Creating the mixtures requires the crafter to make a Craft (alchemy) check equal to the DC of the recipe and taking 1 hour, unless noted otherwise. Most alchemist's kits allow the crafter to make 1 cup (8 oz) of a single potion at once. If the check is failed, the time and materials are lost.
Potions, once crafter, last one week before becoming inert. If a crafter adds preservatives to the potion, it will last up to a year before becoming inert. Preservatives cost 1gp per ounce. Each ounce of preservatives can preserve up to 10 ounces of potions. Preservatives must be added during the creation of the potion or they have no effect.
One of the main sources of materials for making potions is harvesting them from monsters. In order to harvest materials the harvester needs to know what to harvest from the creature. If a harvester has previously harvested a part in question successfully, they know about the part. If not, the harvester can make a knowledge check applicable to the monster with a DC based off of the part. A harvester can also learn about parts from appropriate books or other sources of knowledge.
To harvest a part, the harvester makes a survival check of a DC equal to the DC of the part being harvested. Except where noted, a part must be harvested within 5 minutes of the creature's death, or it will be useless, and harvesting takes 1 minute per attempt. Attempting to harvest parts without a harvester's kit imposes a -2 penalty to the check.
Once harvested, a part lasts for 24 hours before becoming inert, unless stated otherwise. If harvested without a harvester's kit, the part only lasts for 1 hour before becoming inert.