Canvas Backing Boards: Essential Protection for Your Paintings

All paintings should have backing boards as a preventive conservation measure. Installing a canvas backing board on an auxiliary support (stretcher or strainer) will protect the painting from mechanical damage from behind, prevent dirt and debris from falling between the lower stretcher/strainer bar and the canvas, buffer fluctuations in relative humidity (RH) by enclosing the reverse of the painting; reduce vibration of the canvas in transit; decrease the painting’s sensitivity to shock; and discourage the practice of attaching labels to, or writing on, the back of the canvas.

To fulfill these functions, the board must be strong and rigid, and it must be sealed against the reverse of the auxiliary support to reduce air circulation. It should also be lightweight and have low permeability to moisture, although ideally, it should be used in combination with a hygroscopic material capable of absorbing and releasing moisture.

The humidity protection afforded by the backing board is greatly enhanced if the painting is framed behind glass or an acrylic sheet (Plexiglas). The glazing will provide additional protection against day-night environmental cycles and can provide long-term protection over many weeks. Vibration of the canvas under normal handling conditions will also be reduced.

Excerpt from the article by the Canadian Conservation Institute:

https://www.canada.ca/en/conservation-institute/services/conservation-preservation-publications/canadian-conservation-institute-notes/backing-boards-paintings.html