A blueprint is a schematic that allows efficient creation of a specific item. Crafting does not need a blueprint, and most crafting in Greyhawk is done without blueprints. A blueprint reduces the cost of that item's creation by 25%. The blueprint only covers the exact item is it made for—no modifications allowed.
A blueprint can be created as an item that costs ten times as much as making the item it is a blueprint for. Note that this increases the level you have to be to make the blueprint. The cost of making a copy is twice the cost of the item the blueprint is to cover. Blueprints can be copied without restriction, but must be copied in painstaking detail to work. This makes the price of blueprints extremely variable—if the blueprint is a closely guarded secret it is worth up to twenty times the cost of the item it is for. If the blueprint is well known, it might be worth as little as the cost of two of the item to be made.