Oil Mediums: Using Less, Staying Lean
How to use oil painting mediums sparingly, keep early layers lean, and avoid a slippery, slow-drying film.
An oil medium changes how paint moves and how much oil is in the film. That is the entire job. It is not a vitamin. Paint from the tube already contains enough binder to hold the pigment. Adding medium is a small adjustment for a dry, stiff passage or for a glaze. Adding it by habit is how pictures become slippery, yellow and slow.
Lean early, richer later
Fat over lean means a later layer should be at least as flexible and as oily as the one under it. Early layers can be paint used straight, or paint thinned modestly. Later layers can carry a little more oil if they need to flow. Reverse the order, oily soup underneath and lean paint on top, and the surface is more likely to crack as the layers dry at different rates.
Underpainting: A Quiet Start for Stronger Oils wants that lean start. Glazing for Luminous Colour is one of the few moments when a medium earns a place, because a glaze is a thin, oily film by nature. Even then, thin means thin. A glaze is not a puddle.
Solvent is not a medium to bathe in
A solvent thins paint by diluting it, and too much of it leaves a starved, chalky film with too little oil to bind the pigment. Use it to loosen a first drawing-in, then stop. If the paint looks watery and the surface looks matte and underbound when it dries, you thinned too far.
Ventilate the room if you use solvent at all. Keep jars closed. Do not eat at the palette. Oily and solvent-soaked rags should be spread to dry or kept in a metal tin with a lid, not piled in a heap. These are ordinary precautions. Alla Prima: Finishing an Oil Study in One Sitting moves quickly, which is when a jar gets left open. Close it when the brush is not in it.
Linseed and the temptation to gloss
Linseed oil is a traditional binder. A drop can loosen stiff paint. A spoonful makes a glistening mixture that dries slowly, wrinkles in thick patches, and yellows more than the paint would have done alone. If you want gloss, wait for a proper varnish on a cured painting rather than stirring gloss into the colour. The two jobs are not the same.
Other prepared mediums exist. Follow the maker's proportion if you use one, and start under that proportion. No medium repairs a drawing. If the form is wrong, a smoother brushstroke only delivers the wrong form more neatly.
A test you can feel
On a scrap board, paint one patch straight from the tube and one with the amount of medium you usually add. Leave them a day or two. The tube paint should be enough for ordinary notes. If your usual mix is still tacky and translucent when the plain paint has set, you are using too much. Adjust the hand, not the speech about tradition.
Keep medium in a small dip, separate from the piles of colour, and touch it only when a stroke will not otherwise leave the brush. Most of the painting should look like paint.
Frequently asked questions
Do I have to use solvent? No. Many painters thin early paint with a little oil or use the tube as it is. If you avoid solvent, you still need the fat-over-lean order, and you still should not drown the pigment.
Why is my paint wrinkling? A thick, oily layer is a common cause, especially over a layer that dried faster. Scrape excess medium out of the habit, keep impasto to stiffer tube paint, and let layers dry.
Is a bottle labelled medium safe to invent recipes with? Use it as the label suggests. Mixing your own cocktails from unidentified cupboard bottles is how films fail. If you do not know what is in it, do not put it in the picture.