The History of Paper - American Forest and Paper Association

: To prevent ink from spreading and to add rigidity, paper can be "sized" with substances like animal glue, vegetable gums, or rosin. Writing a "Solid" Academic Paper

: Historically, solid paper was made from rags (linen or cotton), mulberry bark, or hemp. These materials are cut, mashed into a paste, and mixed with water to create a slurry called "furnish".

To create a durable, "solid" sheet of paper, you must focus on the preparation of pulp and the removal of water.