What does sizing a canvas mean?

What is sizing?

Sizing is the method of sealing the surface and forming a barrier layer between the support, and the ground and paint layers. When a layer of sizing is applied, it decreases the absorbency of the support. In the absence of this layer, the cellulose fibres of the support can soak up oil from the ground and paint, leading to it rotting.

If you’re using oil painting primer, you need to size your canvas with rabbit skin glue. Sizing needs to seal the surface and sit on the canvas to prevent anything going into the pores.

What’s the difference between sizing and priming?

While sizing is about sealing the surface to protect your canvas, priming creates an even surface to work on. Oil primer offers a smoother surface, whereas thixotropic and acrylic primers offer more tooth.