Here's an interesting article (http://www.economist.com/blogs/babbage/2012/07/printed-books), especially because it has the perfect explanation of how a deckle edge is formed when making paper by hand. (The deckle edge is that feathery edge to handmade paper):
Paper begins as a suspension of fibres in a water slurry that is drained through a screen. A frame temporarily placed around the screen to restrain the mixture in place is known as a deckle. A papermaker lifts the deckle after draining sufficient water and before pressing the paper with felt and continuing the process to a finished sheet.
The deckle cannot make a perfect seal against the screen, and fibres seep under its edge, which creates the rough-edged pattern.