Dust
Dust raises the Success Rate of an enchant book. It starts as Secret Dust, which you open to find out what is inside.
Secret Dust
Secret Dust is an unidentified satchel. Right-click it and it becomes either Magic Dust or Mystery Dust. The range on the item shows how much success the Magic Dust inside can give.
Magic Dust
Magic Dust adds its percentage to an enchant book's Success Rate. Drop it onto a book of the same rarity.
Two Magic Dust of the same rarity can be combined into one of the next rarity up at the Alchemist.
Mystery Dust
Mystery Dust is what a Secret Dust gives when it does not turn into Magic Dust. It does nothing on a book.
Omni Dust
Omni Secret Dust and Omni Magic Dust work the same way, but on a book of any rarity.
Where dust comes from
The Tinkerer turns an unwanted enchant book into Magic Dust of that book's rarity (between 1% and 20%). Dust also turns up in lootboxes and event rewards.