Pourquoi enduit-on les toiles avant de peindre? - C'est pas sorcier

Well, if we painted directly on the linen, the paint would pass through the support. In addition, it would soak it exactly like the ink on the buvar paper. Indeed, when we observe the linen in the magnifying glass, it presents itself in the form of a mesh with empty spaces between the meshes where the paint can slip. If we want to paint on this support, we have to plug the holes, waterproof it with glue. However, glue has a big flaw. It forms asperities on the surface of the canvas. If we want to paint on this canvas, we have to smooth it with a chalk-based putty. And this putty will also protect the canvas. Indeed, when we paint with oil, the oil degrades the cellulose of the linen. By making a screen between the linen and the paint, this putty will avoid the destruction of the canvas.