Massage the Medium
Blending oil paints is like kneading bread dough.
Kneading is the process that brings the bread dough ingredients together, activates the wheat's gluten protein, and yields a silky-strong dough ready to be baked. Kneading massages the yeast into activity, which reacts with the wheat proteins, forming a glutinous mass. The process must take effect (“rise”) before the loaf of dough is baked in the oven.
Un-kneaded dough tends to spread-out flat. The baking dough can unexpectedly fall back into itself, collapsing the loaf, if the dough is not given a chance to rise. And if an insufficiently kneaded loaf of dough is baked the baked bread loaf will be heavy -as well as flat. This may be the intended effect if flat bread is desired.
How do you know if bread dough is kneaded enough? Dough is ready when it passes the elasticity test. To find out, tear off a chunk of dough and stretch it between your fingers. If the dough tears, you haven't kneaded it enough, and is in need of more kneading. If it stretches without breaking, exhibiting an elastic effect, the dough is ready for the oven. (April 5, 2019 Tasteofhome.com Magazine)
The vegetable oil used as blending medium by oil painters is subject to a chemical reaction in response to physical massaging and exposure to air. Although an oil painting is certainly not baked, temperature will have an effect on the drying time of the oil painting. As every oil painter knows, an oil painting requires prolonged drying before final varnish is applied, or else any residual uncured oil paint will smear.
Just as frying food with unsaturated cooking oil works by forming a stick-resistant coating, or glaze, on the skillet under frying temperature, so does the oil medium used by painters form a glazed, or glassy coating, under long exposure to air at room temperature. And, just as frying residue is not easily removed by rinsing, that is, not without dish washing detergent, scrubbing pad, and elbow grease, so oil paint eventually hardens into a permanent coating.
The discovery of Teflon, and similar coatings, made greasing the frying pan unnecessary. Of interest to artists, Linoleum floor tile was made by taking advantage of the tough emulsion effect of drying Linseed oil. It is incredibly durable—as everybody knows—and attractive to look at. Black-and-white checker board pattern Linoleum flooring is possibly the most distinctive feature of the Mid-Century Modern aesthetic. Picasso made Linocut printmaking famous.
The attraction linseed oil has for painters can be explained by its mechanical and optical properties. While drying, linseed oil aggressively reacts with oxygen to form the thin, continuous film that gives an oil painting its distinctive gloss. Students of oil painting are admonished not to thin oil paint with solvents. Thinning makes the viscous paint stuff easier to ply, but breaks-up the fatty acid chains before they can naturally dry to a mellow sheen.
Would the modern chemistry of polymers have interested Leonardo? He was chided by his associates for wasting precious creative time on random mixtures of substances known to dissolve in vegetable oil in search of the perfect medium. He must have wondered why some mixtures dried hard as glass, but cracked, while others never dried at all. Today, specific effects can be predicted of oil paint-friendly aromatic esters, some of which will rescue aging masterpieces from a dismal obscurity.