Fate Core: Reserve Skills

So had an idea about extras that cost skills.  Reserve skills.  They are skill extras with specific effects but don't often, if ever, roll as skills.  They increase in rank and can be a place holder in skill columns.  I have an example below based on fantasy alchemy.

Reserve Skill:  Alchemy

  This reserve skill grants the PC an alchemy pool equal to double the rank in the skill.  This pool represents the alchemical materials the character has on them.  The PC may take actions to spend from this pool to create potions.  No potion may have more points from the alchemy pool then ranks in this skill.  Potions last until they are consumed or milestones.  At each milestone all potions spoil and the alchemy pool refreshes.  To start players with this skill can forge skill potions.  These potions are used to grant a bonus equal to the points spent for their next roll with that skill, then one less each test with that skill until the value returns to normal.

Stunts

Herbal gathering:  Once per game, spend a fate point and make a lore check, regain half the result to your alchemy pool.

Explosives:  Spend 2 from your alchemy pool and make a lore attack to everyone in a single zone adjacent to the one your are in.