Tan Leather is a Lunar spell which tans up to 5 hides from the player's inventory per cast. Using this spell does not require extra GP to tan per leather as you would pay by visiting a tanner. Casting this spell requires the completion of the easy, medium, and hard tasks in the Fremennik Diary.

With optimal timing, this spell is capable of tanning 8,000 hides per hour, giving roughly 130k experience per hour. You may tan a Cowhide into either soft or hard leather using an option found when right-clicking the spell icon.

A Magic level of 78 is required to cast this spell, giving 81 experience. It requires 1 Nature rune, 2 Astral runes, and 5 Fire runes to cast.