deckle

In manual papermaking, a deckle is a removable wooden frame or "fence" placed into a mould to keep the paper slurry within bounds and to control the size of the sheet produced. After the mold is dipped into a vat of paper slurry, excess water is drained off and the deckle is removed and the mold shaken or "couched" to set the fibers of the paper. Some of the paper slurry passes under the deckle and forms an irregular, thin edge. Paper with a feathered or soft edge is described as having a "deckled" edge, in contrast with a cut edge.

Machine-made paper may artificially have its edges produced to resemble a deckle edge. This is most commonly used for private presses or fancy stationery.

In film processing, deckles are die inserts that set the coating width of a slot die coater or the extrusion width of an extrusion die. They work by constraining the flow as the material exits the die. Since some materials have a tendency to neck in or spread out after leaving the die, deckle position may need to be compensated to achieve the target width.