Canvas - Cotton or Linen?

What is the difference between cotton and linen?

Cotton is relatively affordable and is used by both beginners and professional artists. Cotton duck, or raw, unprimed cotton comes in different weaves, weights and strengths, and can be bought unprimed or pre-primed. A good 10-12oz cotton duck with a tight weave, sealed with rabbit skin glue or a synthetic equivalent and primed with a quality gesso, will provide an adequate, durable painting surface, particularly for acrylics. The elasticity of cotton also lends itself to easy stretching.

Linen is the classical surface for oil painting and the preferable one for acrylics. Linen is woven from flax, which has a greater natural strength, a longer fibre, and a higher resistance to decay than cotton. The natural oils of flax are retained in the fibre of linen, preserving flexibility, and preventing the canvas from becoming brittle. These oils also provide the optimum surface to bring out the intensity of your paint colour. Linen can be bought in its raw state, sized (clear-sealed with rabbit-skin glue or synthetic equivalent) or primed with additional layers of oil or universal primer. It is available in different grades and textures. A smoother and finer surface is best suited to artists working in fine detail and thin layers; rougher surfaces have a less regular texture and are ideal for impasto technique.

Pre-Primed Canvas

It is prudent to be sure of all substrates an artist is to employ. Even the most reputable brands sometimes appear to focus more on the quality of linen and frame and use a primer that may not always stand up to the conditions that are required of them.

As suggested by Derivan: Surface Preparation | Matisse

If the artist wishes to be sure of the ground they are to work on, lightly sand back the pre-primed surface (do not sand back all the way to the canvas). Apply one coat of MM10 Gesso mixed equal parts with water. The next coat can be straight Gesso or may be diluted depending on the required surface.