Fat over lean refers to the principle in oil painting of applying paint with a higher oil to pigment ratio ('fat') over paint with a lower oil to pigment ratio ('lean') to ensure a stable paint film, since it is believed that the paint with the higher oil content remains more flexible.
Oil paint dries at different rates due to the differing siccative properties of the constituent pigment. However, everything else being equal, the higher the oil to pigment ratio, the longer the oil binder will take to oxidize, and the more flexible the paint film will be. Conversely, the lower the oil content, the faster the paint dries, and the more brittle it will be. Ignoring this practice, even in some alla prima painting, may result in a cracked and less durable paint film.
It has been claimed by some paint manufacturers that the 'fat-over-lean' principle can be circumvented by using synthetic, alkyd-based painting media such as Galkyd and Liquin. These media do provide consistent drying times, increase the paint film flexibility, and promote adhesion between paint layers. However, since classical painting media, turpentine, natural resins, and certain plant oils (linseed, walnut and poppy), applied properly, have lasted for centuries, some artists choose to avoid synthetic media since their long-term stability is unknown.
Famous quotes containing the words fat and/or lean:
“The opera isn’t over till the fat lady sings.”
—Anonymous.
A modern proverb along the lines of “don’t count your chickens before they’re hatched.” This form of words has no precise origin, though both Bartlett’s Familiar Quotations (16th ed., 1992)
“Blind mouths! that scarce themselves know how to hold
A sheephook, or have learn’d ought else the least
That to the faithful herdman’s art belongs!
What recks it them? What need they? They are sped.
And when they list their lean and flashy songs
Grate on their scrannel pipes of wretched straw,
The hungry sheep look up, and are not fed,”
—John Milton (1608–1674)