Most naturally occurring cellulose is in the cellulose I crystalline form, but because of biosynthetic and isolation processes, its surface is rough and porous, and thus unsuitable for many quantitative surface characterization techniques. It is possible to make smooth surfaces by dissolving cellulose in certain complex solvents, and casting or regenerating cellulose films, but in this case the cellulose is in the Cellulose II or amorphous form, and thus not representative of cellulose in nature. However, our cellulose nanocrystals are composed of Cellulose I (stabilized by a minor amount of anionic sulphate ester groups on the surface that can be removed by gentle heating), so by careful casting of films from aqueous nanocrystal suspensions, it was possible to make extended smooth (root-mean-square roughness on the order of 1 nm) Cellulose I surfaces. ["Smooth Model Cellulose I Surfaces from Nanocrystal Suspensions." C. Edgar and D.G. Gray, Cellulose, 10(4), 299-306, (2003).] These surfaces are suitable for surface force and friction measurements on pure natural cellulose. [Friction and forces between cellulose model surfaces: A comparison. Johanna Stiernstedt, Niklas Nordgren, Lars Wagberg, Harry Brumer, Derek G. Gray, Mark W. Rutland, Journal of Colloid and Interface Science, 303(1), 117-123 (2006)].