Here's why it's used:
* Support and Strengthening: Old canvases, especially those painted on linen, can become fragile and stretched over time. The lining provides a strong backing to prevent the canvas from sagging or tearing.
* Consolidation: The lining helps to reinforce the paint layers and prevent cracking or flaking.
* Protection from Environmental Factors: The lining acts as a barrier against humidity, dust, and other environmental elements that can damage the painting.
* Stabilization: In some cases, the lining can help to stabilize the painting if there are areas of warping or distortion.
* Removal of Previous Linings: Sometimes, you might find multiple layers of lining on a painting. This is because, over the centuries, paintings have been relined multiple times as needed.
What kind of paper is it?
The paper used for lining is usually a strong, acid-free paper, sometimes even canvas, to ensure it doesn't damage the painting. The brown color is often a result of the aging process and the type of natural materials used in the paper.
Important Note: While the lining is essential for preserving the painting, it can also be a valuable source of information about the painting's history. For instance, the paper's age and condition can tell us about the conservation and restoration efforts it has undergone.