One important thing to think about when painting solvent free is the texture of your canvas or support. Without solvents the paint is thicker and doesn’t apply as smoothly. More rough texture causes more drag on the brush making the paint harder to apply smoothly. This can be to your advantage if you want lots of texture and aren’t too concerned about smoothly blended paint. However if you want the paint to apply as smoothly and blend as easily as possible it is best to have a nice smooth surface.
Linen is renowned for allowing the brush to ‘glide’ over the surface whereas cotton canvas is bit rougher and stickier. Painting on panel or board is the smoothest you can get and the paint blends and applies incredibly easily and smoothly. You can usually only go so big with panels though so if you want to paint on cotton canvas it’s best to try and find the smoothest canvas you can get. Canvas comes in many different textures and thicknesses and it is sometimes quite hard to tell what the texture is like without feeling it in person.
I have read that the Old Masters used to spend months getting their canvases ready for painting. They too liked the canvas to be incredibly smooth and the lead white oil grounds they used took quite a long time to dry. They used to sandpaper between each layer of ground to build an incredibly smooth surface.
When I’ve stretched my own canvas I always do the same process, making sure each layer is nice and smooth before apply the next layer of gesso. When buying canvases pre-stretched I don’t know how much effort they put into smoothing out each layer of gesso. It always seems a little too rough to me. Because of this I sand the canvas lightly with a fine sandpaper before commencing painting.
Along with my techniques on glazing without solvents I have found that this really helps smooth out the paint and brush strokes in solvent free oil painting.