Boneskin potion

This can be crafted at Lysis from 3 bones and about 500 gold, the bones drop from skeletons in the desert, which is accessible from the maze:

The potion turns your skin white and adds 18 defense:

The boneskin potion is said to be level 20. At 21 drinking skill, I gain 3% xp from absinthe and 6% xp from boneskin potion. The market price for absinthe is about 500 gold, so it seems more efficient for now since I don't expect people to sell boneskins as low as 1000. They will probably be better for training at higher levels since xp tends to drop rapidly as you outlevel mobs/potions/scrolls.