Process:
- Brew two CL 15 Death Armor potions.
- Combine the two potions into one stack.
- Split the stack back into two potions.
- The potion remaining in the original stack will last for 90 seconds. Any potions that are merged into this (original) stack will also last for 90 seconds.
- The potion that is split off from the original stack will last for 18 seconds. Any potions that are merged into this (split off) stack will also last for 18 seconds.
- The potions in both stacks ('original' 90s and 'split off' 18s) will still state in the description that they are "Casterlevel 15".