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How does changing humidity affect a canvas painting?

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Inside the ongoing preservation of the Vatican — Art conservation and restoration Learn about the restoration of tiles in St. Peter's Basilica, Vatican City.

In the context of art conservation, a canvas support is sensitive to its environment. When there are variations in relative humidity, the canvas will expand and contract.1

While this effect is generally less drastic for canvas than it is for wood-panel supports, these fluctuations can still lead to significant condition problems. As the canvas moves, the paint and ground layers—which are often less elastic—may lose their adhesion to the surface. This can result in various forms of damage, including:12

Cleavage: The separation of paint or ground layers from the support.1
Flaking, blistering, or scaling: The lifting of paint from the surface.1

To mitigate these risks, professional conservators emphasize the importance of maintaining a stable environment for artworks. While specific treatments like "lining" or the use of suction tables can address existing deformations or paint loss, the primary goal in modern conservation is to prevent damage by controlling the surrounding climate.21