UNDOCUMENTED MECHANICS
30% of the potions found are mana potions.
10% of the potions found are rejuvenation potions.
"chance" above follows a diminishing curve, not a flat gain per level; the other numbers in the same block do not: 15% at level 1, 50% at 5, 68% at 10, 84% at 20, 100% at the limit. Reaching the limit takes skill level 60, gear bonuses included, so the first few points are worth far more than the last ones.