MITRA Forum Question Details

​That's a good question!  Printmaking papers, including Rives BFK, are usually internally sized so that absorption of ink/paint/other media is controlled during the printmaking process.  To my knowledge (I'm a paper person, not a paintings person though!) canvas is not internally sized, so in order to achieve control of your printmaking media on the canvas surface a ground (i.e. the gesso) needs to be applied.

As stated, most high quality printmaking and watercolor papers have internal sizing. Some watercolor papers also have surface sizing. This diminishes oil absorption. Unprimed artists canvas and linen should have no existing size unless specifically purchased this way (I remember David Davis used to sell linen pre sized with rabbit skin glue as one of their options. Canvas like this is far harder to stretch and I could never see the advantage).

Additionally, printmaking inks are generally bulked up with magnesium Carbonate to stiffen the ink. So, almost any oil paint that you would encounter would be far fatter than a similar printmaking ink. Finally, unless the oil paint is applied neat, with no solvent or medium, it is always going to be substantially looser than the ink.

Sizing isn't just for the purpose of protecting the support, it's also to prevent paint from becoming underbound. Paint applied on raw canvas loses vehicle to the support quickly.