Here you will find the various component items that can be used to create something more powerful.
Here you will find the various recipes, current and retired, that have been available in Castle Age.
Alchemy items can be combined to summon monsters, unlock quests, or to create generals or items not available through other ways. Gift items are often not very powerful on their own but combined through recipes can create something quite powerful.
The Annihilator treasure chest contains a number of Class Abilities of level 1 and level 2. On the Alchemy page there is a tab where you can combine a Level 1 and a Level 2 ability into a Level 3 ability.
In late 2010, Castle Age introduced the Goblin Emporium to help soak up the gifts you no longer wish to combine into their resulting item. Not every item may be traded in and the item you receive is randomly assigned, but the items you get out are generally worth the trouble. Along with many mid-level items like the Deathrune Signet, there are two Emporium-only items.