Tight'n'Up Liquid Canvas Retensioner tightens up loose canvases without having to re-stretch the canvas. This spray removes wrinkles and sags from most stretched canvases. Apply to the back of the canvas behind the affected areas or the entire canvas, and underneath the stretcher bars. The water in Tight'n'Up causes the canvas threads to swell up, thereby shrinking their length, consequently tightening the canvas. Acrylic binders in the formula seep in between the canvas' threads, providing extra support to the fabric. When the water evaporates, the acrylic remains in the canvas and prevents it from relaxing to its previously loosened state, thereby retaining the increased tension. Apply before or after painting. Acid free and archival.