Here my dilemma today. I need to fill a 36 × 36 Canvas with a base color. I need the paint to be really fluid/wet so as to have a very smooth surface (no brush strokes) and be able to blend monochromatically to give some depth. I am getting all kinds of mixed messages about how to handle the paint itself. Some say use galkyd slow dry with a bit of turpenoid, but I have read that the paint can “wrinkle”. Some say use liquin but it will take forever to dry…
I’m personally not a big fan of alkyd-based mediums, especially in multi-layered paintings. Also, I hate the way they smell.
Here’s what I’d do. I would thin the paint very slightly (I like real turps or spike, but not everyone likes the smell, so you can use mineral spirits if necessary). Make sure you have excellent ventilation. I’d apply the paint with a wide, soft brush, getting it reasonably flat. Then I’d take a clean soft flat or fan brush and dip it in solvent. With a very soft touch, I’d whisper it over the surface of the painting, knocking down flat spots. This would take a long time for a 36 × 36 canvas. I’d let the canvas dry flat in a dust-free room (or covered by a jury-rigged plastic “tent” to keep dust off of it).
Another option would be to add a bit of thinned stand oil to the paint. Stand oil tends to level brush strokes and dry hard and glossy, especially when the painting is allowed to dry flat to avoid sagging. For layers after that, you’d need to take steps to ensure adhesion to the glossy base layer, such as wet sanding or using a medium containing a balsam.