Canvas is a durable cotton fabric for painting on .... and that's where many artist's knowledge of canvas stops.  When buying canvas you are going to find that the shop will probably stock different types. If you've been blindly buying your canvas maybe you have just gone with whatever is cheapest, on sale, or more expensive (guessing that it must be worth it somehow).

Here's what you need to know about canvas so that you can make an informed decision.

Primed OR Unprimed? 

Primed Canvas - comes with a layer of white gesso on it. Once stretched you can begin painting if you are happy with that surface to work on. However, the work you do in priming the surface can really affect the rest of your painting - so just keep that in mind : )

Unprimed or Raw Canvas - will require more surface preparation once stretched but some artists like this because they can control the quality of the surface preparation - using a good quality gesso and PVA size for example.

From 7oz being the lightest weight/thinnest to 10 duck being the heaviest weight/thickest.

There will be different weights of canvas from thin fabric to thick and heavy fabric. I've listed them below from wimpiest to most robust !  (AKA from thinnest to thickest)

1.   7oz - light weight canvas, quite thin, may require quite a few layers of gesso to build up a nice surface before you paint it. 

2.   10oz - still on the light side but more durable than the 7 oz

3.   13 Duck - Heavy weight canvas but has a smooth texture - very nice if you want to minimize the look of the typical texture of canvas. It takes less prep work to get this canvas primed to a nice smooth finish.

4.  12 Duck - Heavier weight than the 13 duck and a little courser texture to the surface.

5.   10 Duck - Heavier weight than the 12 duck and a little courser texture to the surface. At this weight you really have to pull when stretching as it has little "give" to the fabric.

 When should you use a heavy weight canvas?

-If you are very vigorous with your method of paint application.

-Sometimes even the use of palette knives can poke holes in canvas depending on how you use them...this is easier to avoid with heavier weight canvas.

-Another time to consider using a heavier weight canvas is when you are making large paintings. The larger the painting, the greater the risk  for damage because of their weight, size and awkwardness to move and ship.