Bag of Grinding (but better)

This magical bag embodies the ever-changing chaos of Limbo by harnessing its powers to change physical material to something else but keeping magical essence intact. 

upon placing a magical item in this bag you can use one charge to activate the bag. 
when activated roll a d20, on a 1 the new item will be one rarity lower than the old item, on a 2-19 the rarity of the new item is the same as old, and on a 20 the new item is one rarity higher than the old item. 

the bags charge recharge at dawn. 

doesnt work on potions