Delve into darkness

This spell, when cast, turns the caster and any objects or people invisible. They can phase through things at will, or at the caster's discretion. The caster uses up one bottle of pure darkness upon casting. The duration of the spell depends on the caster's spellcasting modifier. (12 spellcasting modifier=12 minutes) The caster and targets can move anywhere they want, and they can interact with objects, but the objects stay visible. At levels 2, 3, 4, 5, 6, 7, 8, 9, and 10 increase the range by 10 feet.