ideally stored in a stable environment with constant temperature and 30% (± 5%) relative humidity. If vellum is stored in an environment with less than 11% relative humidity, it becomes fragile, brittle, and susceptible to mechanical stresses; if it is stored in an environment with greater than 40% relative humidity, it becomes vulnerable to gelation and to mold or fungus growth. Additionally, the relative humidity needed to properly store vellum is not compatible with optimal humidity level for storage of paper, which can pose a challenge for libraries. The optimal temperature for the preservation of vellum is . See also History of hide materials Calfskin Parchment Notes References Hepler, Dana J., Paul Ross Wallach, Donald Hepler, "Drafting" in Drafting and Design for Architecture & Construction, 9th edition, 2012, Cengage Learning, , 9781111128135, Google Books Stokes, Roy Bishop, Almagno, Romano Stephen, Esdaile's Manual of Bibliography, 6th edition, 2001, Scarecrow Press, , 9780810839229, google books External links On-line demonstration of the preparation of vellum from the BNF, Paris—text in French, but mostly visual. Book design Calligraphy Hides (skin) Writing media