To cleave is to split or divide. Curiously, "cleave" can also bear the opposite meaning: to adhere closely, cling, stick."Cleavage" is sometimes used to refer to the partial separation or flaking of paint from a canvas, ground, or other layer of paint. Flaking usually reflects a breakdown in adhesion between the paint layer and the support. The problem may be inherent in an artist?s choice of materials or may result from the deterioration of the glue size in the ground. Such conditions are aggravated by seasonal or artificial climate control changes in temperature and relative humidity. The support expands under humid conditions and contracts under dry ones. As a paint film ages it loses its elasticity and becomes even more susceptible to flaking, cracking and cupping. In treating flaking paint, an art conservator typically infuses an adhesive into the flaking area and applies weight during the adhesive's setting period.Also see carve, chisel, and hygrothermograph.