Common menu bar Breadcrumb CCI Notes 10/9 Keying Out of Paintings Introduction Paintings on canvas have a tendency to become slack on their auxiliary supports (i.e., stretchers, strainers). In certain circumstances, a procedure called keying out can be performed to tighten the canvas on stretchers with expandable corner joints. However, if keying out is performed when it is not necessary, or if it is incorrectly executed, serious damage to the painting can result. Anyone undertaking keying out should be aware of the correct procedure and of its limitations. Keying out is not a routine or basic procedure. If there is doubt concerning its application, seek advice from an experienced conservator before undertaking keying out. Paintings and the Environment Paintings respond to fluctuations in relative humidity (RH). It is important to realize that all components of a painting (i.e., wood, canvas, glue size, ground, and paint layers) respond to changes in RH. The overall response of a painting to its environment will vary from one painting to another, depending on the materials present and on the individual reactions of each material. When RH drops, the paint, ground, and size layers lose moisture, contract, and become increasingly stiff and brittle. In this condition, the layers are most highly stressed and their ability to accommodate dimensional change without cracking is reduced. With increasing RH, these layers gain moisture and become more flexible. However, above approximately 85% RH, the canvas may have a tendency to shrink. Expansion and contraction of the wood stretcher will