the canvas. This distortion may be reduced simply by improving the framing method (see CCI Notes 10/8, Framing a Painting , and CCI Notes 10/10, Backing Boards for Paintings on Canvas ). When Should Keying Out be Undertaken? Whether one should be concerned about slackness depends largely on the storage, display, and travel plans for the painting. Generally, slackness in a painting that is permanently stored or displayed in a museum will not result in immediate damage. Therefore, a slack canvas may be observed over a period of time without risk to the condition of the painting. However, if a painting is to travel, flapping of a loose canvas can result in damage to the painting. The behaviour of a painting in response to its environment has tremendous implications for keying out. If keying out is necessary, it should be undertaken mid-way through the RH cycle to which the painting is exposed. For example, in an uncontrolled environment that fluctuates between 20% and 80% RH, keying out should be undertaken when the RH is between 50% and 60%. Never undertake keying out during extremes of RH or temperature, particularly during periods of low RH. In low RH, components of the painting become stiff and brittle. Keying out at 30% RH is two to three times more stressful for the painting than keying out at 50% RH. Precautions Keying out is a potentially damaging procedure that must be undertaken with extreme caution. Keying out of a rectangular stretcher is not an