A canvas painting that has gone slack renders the painting subject to gravity as well as other forces that will weaken and damage the original surface.
A taut canvas, one stretched to the proper tensile strength, is the foundation of health for an oil painting.
When the canvas is slack, the paint can easily begin to flake and chip; in general, the surface becomes far more susceptible to tears and rips. In addition, slack canvas encourages such dangerous factors as humidity and micro-organisms to begin to invade the paint layer and further compromise the work.
Often the canvas can be made taut with the use of adjusters on the back of the painting. At other times the work will need to be removed from the stretching bars and reattached in order to bring the canvas up to the proper tensile strength.
When the canvas has been stretched properly, it will help keep the painting stable for twenty to fifty years before the procedure needs to be done again.
