PRIMING THE CANVAS
This blog is specifically relating to painting with oil.
Recently I have had quite a few bad experiences regarding pre primed canvases. The main reason why canvases are primed is to protect the canvas from direct contact with oil paint. In time, the canvas will get damaged if it is not primed.
If you buy a primed canvas and then you paint on it and you find that the paint has gone through and it shows on the back, then it has definitely not been well primed, even if it was an expensive canvas. This is the reason why I always ask my students to add an extra coat of primer to their already primed canvases from the art shops. I just wont take the risk any more, especially when it comes to using colour shapers. A ruined canvas can feel like a ruined orgasm.
If the paint does not come through the canvas but it does have a problem with flow and feels sticky, simply cover the canvas with paint mixed with a little linseed oil using a big brush. If you still have a problem, use lots of white paint to cover the canvas and leave it to dry. It might take longer to dry, just be patient. Once it is dry, the surface will be fine for painting.
If you are beginning with raw canvas, I would firstly do a coat of wood glue eg, pva. This will provide good protection for the canvas. I love doing that first coat with a palette knife, it glides on beautifully. Leave it to dry and then lightly sand it. Simply run your hand over the sanded area and the non sanded and you will feel the difference. Canvas has lots of tiny hairs and bits and when you go over them with the palette knife they harden and create rough patches and this is why the canvas needs to be sanded. After this initial coat, you need to do two more coats using gesso and your palette knife. Lightly sand between coats. If you want a nice white finish, I recommend one more coat.
If you are using a brush and dilute the gesso, then you will have brush marks which have to be sanded and you will need more than three coats of gesso. I recommend Atelier brand which is more expensive than others but it has a nice viscosity and thickness which can also be used for texture on the final layer. I sometimes like to play with it and it can lead me in an unexpected direction when I am painting. Gold leaf on top of it can create a great effect.