Commonly, artist canvas is sold "primed" or prepared with a coat of gesso, and ready to paint upon. (Gesso is Italian for "chalk board" and is usually a paint with calcium carbonate - a chalky powder that gives this layer its "tooth".
Most cotton duck and linen is now sold as "universal primed" or "acrylic primed". This means that modern synthetic (acrylic) sealers and gessos have been used to coat the material. Most have two layers and some have three. This makes the material ready to accept paint and to protect the fibres of the material from the effects of the paint/solvents and atmosphere.
Traditionally, most canvases were primed with rabbit skin glue and then an oil based primer or gesso. These canvases are called "oil primed" however synthetic sealers have mostly replaced rabbit skin glue.
The ground serves a number of functions including to isolate and protect the canvas. It provides a bright (or coloured) background for the painting, (glowing through washes) and it offers the paint some texture or "tooth". Different grounds vary in the amount of tooth. This is a personal preference and you will quickly discover which you prefer. It's another reason to experiment with different brands and gessos occasionally. If you find the gesso on which you paint is scratchy and seems to absorb all your paint too quickly, you might look for a less toothy canvas or gesso or make one yourself (see later).
There aren't too many rules, but this is an important one. Acrylic paint will lift off oil based paints in a short period of time.
So that's it. Those are the basics. You might choose:
You are probably wondering which one is best. Unfortunately, there is no single answer to this. (See Manny's art blog)
People who were involved with the sale and collection of works by artist Ian Fairweather became concerned about the materials he would use. Once, they generously sent him some museum quality canvas. Ian used the canvas to mend the tent which was his home on Bribie Island. He continued to paint on cardboard!
The quality of his work did not suffer. Unfortunately its longevity probably will.