This document presents preliminary research into the shrinkage of canvas supports at high levels of humidity. The three-dimensional response of canvas as a woven material is discussed, including the action of longitudinal and transverse yarn swelling as the precursors of shrinkage. A technological context of shrinkage in 19th-century canvas is given, along with directions for further research into the influence of preparation and conservation techniques. An experimental section compares the response of of a new unprepared canvas to a 19th-century primed loose lining using a non-contact, non-destructive technique of analysing images of the weave obtained with a CCD camera at varying levels of RH. An appendix discusses the usefulness of this technique in overcoming the inherent variability of woven material.