There are 2 main types of acrylic primer – regular acrylic primer and gesso. Both are made up of acrylic resins mixed with pigment, they are cheaper than artist acrylic colour because they contain opacifiers to ensure that they provide good coverage. Acrylic Gesso replicates the qualities of traditional gesso, a mixture of French chalk or whiting and rabbit skin glue, and is absorbent with a slightly heavier tooth than acrylic primer – the more layers you apply the more absorbent. Because of this a few coats is required if you are going to apply oil colour to it, as there is a rick of the oil sinking down to the fibres of the canvas support and causing damage. You can also choose to prime your canvas with a black gesso primer by System 3 if you prefer to work on black (this will have a dramatically different effect on your transparent colours). Acrylic clear primer allows you to work on the natural colour of the canvas without having the absorbency of the raw fabric.
Primer dries smoother and is not absorbent, but a few coats with light sanding in between will make a good solid surface on which to paint. The white colour of regular gesso or primer helps colours to maintain their luminosity. All white gessos and primers can be tinted by adding acrylic colour and mixing. Acrylic primer, unlike oil primer, does not cause natural fibres to rot over time so can be used without the use of glue size. Many oil painters today use acrylic primer instead of rabbit skin glue size as it does not require heating, and its whiteness means you need fewer coats of white lead oil primer to achieve a bright white, glossy surface.
Gessos and Primers should be applied to surfaces as thinly and evenly as possible - more thin layers creates a superior surface on which to work than fewer thick coats. We recommend the use of a wide, relatively springy soft hog hair flat brush. Sanding the primer/gesso surface between coats with fine sand or glass paper will create a super-smooth surface.