Oil and cotton don't mix
Oil and Cotton Don’t mix…
Q: I heard that you should not use oil paints on cotton canvas, it that true? What is the difference between cotton and linen, besides the price? What should I paint on with oils?
A: Yes, it is true. That is, if you want your paintings to last for a few decades at least. Oil eats cotton. Cotton canvas for artist’s is unbleached and is a cream color and has little brown flecks in it. Linen is a darker brown, burlap colored fabric, and is more expensive. Linen is a much more durable fabric for a couple of reasons. The fibers that make up the material are longer and rounded, like tiny ropes. Cotton fibers are short, flat strands of unprotected cellulose fiber and are spun together to make up the fabric. Because the linen has linseed (flax) oil in the fibers (this gives it the dark color) the fabric is more durable and is protected from pollutants and moisture in the air. Cotton readily absorbs moisture from the air. This causes it to expand and contract more than linen. As you can imagine, this would not be good for dried oil paint. The absorbent cotton canvas is also more prone to deterioration from any substance that comes into contact with it, like acidic oils (the paints), sizes, or oxygen and pollutants in the air.
A cotton canvas coated with acrylic gesso (which is also porous and absorbent) will suck the linseed oil out of the oil paints. If you look at the back of most oil paintings done on cotton canvas you will see dark patches of oil that have soaked through to the fabric, especially if the paint is applied thick. This acidic oil will then ‘eat’ away at the cotton fibers and the fabric will become weak and brittle within a few years. Worse yet, now the paint layer has been robbed of vital oil that is needed to keep the colors bright and transparent, and the paint layer flexible and durable. I have seen oil paintings on cotton canvas no more than ten years old that are dried out, dull, and cracked throughout. Many artists like to use the ready-made cotton canvases at the art supply store. These are made with very thin cotton (around 6-7oz.) and are coated with a thin layer of very absorbent acrylic gesso that is spayed on – a quick snack for a robust oil painting… The bad news is if you want to make permanent oil paintings on canvas you are going to have to spend more money and you will have to make the canvases yourself, or have them custom ordered or custom made.
Besides cotton and linen there are also some composite fiber canvases out there that are mostly mixtures of synthetic fabrics like polyester and sometimes linen. These are probably good choices for oil painting.
This next question follows up this discussion:
Q: what type of primer (ground) should I use for painting in oils? Is Acrylic Gesso alright?
A: Oil paints can be safely used on hardboard that is prepared first with a size (a thin layer of White Shellac diluted 2 parts Methyl Hydrate – 1 part Shellac is a good choice) and at least 2 coats of acrylic gesso. You can buy the shellac and the methyl hydrate thinner at the hardware store. These are the only products that you can use in permanent painting techniques available at hardware stores! Latex house paint is not a good primer! These commercial paints are not designed for artist’s purposes and are specifically engineered to deteriorate after a few years.
Oil paints will probably not adhere well to acrylic gesso on canvas. Imagine what happens to a dried layer of oil paint on a plastic bag that is being stretched. This is an exaggerated example of what would likely happen when the canvas expands and contracts. The best flexible support (canvas) for oil paintings is linen (or one of the newer synthetic fabrics) sized with Poly Vinyl Acetate (PVA) then coated with an oil ground (primer). You must let the primer dry thoroughly for several weeks before painting.
Recent research and development has seen changes, and improvements in the products used to prepare canvases for oil painting. Animal hide glue, generically referred to commercially as Rabbit Skin Glue was the size of choice for hundreds of years. The purpose of a size is to protect the canvas from coming into contact with the oil from the primer/paint layer. The disadvantage of the animal glue is that it absorbs and releases moisture causing it to expand and contract. This of course may cause cracking in the paint layer. Hide glue also yellows and becomes more brittle with time. Its modern replacement is the PH neutral PVA that can be used on both sides of the canvas to both insulate it from contact with the oil and protect it from atmospheric pollutants and moisture. It is available in art supply stores. The other modern innovation is an oil primer that uses an alkyd resin instead of the traditional linseed oil as a base. It dries quicker and is more flexible.
So go to the art supply store and spend some more money! If you want more detailed instructions on how to prepare a gesso panel and canvases for oil and acrylic paintings drop me a line or I may post the info on the FCA website… thanks for the Q’s.
