Fat over Lean
Do you ever get mixed up on this golden rule of painting with oil?
Which one is fat again? And does it apply to all types of oil painting?
Here’s how I first remembered the golden rule of Fat over Lean.
Fat is oil paint with Oil (fat) added
Lean is oil paint thinned with a medium
Here’s the low down on the Fat over Lean principle.
Oil paint is made up of pigment and oil. It doesn’t evaporate. It’s fairly oily straight out of the tube and it takes a long time to dry. Six months to a year to dry completely. The outside dries first as it is in contact with the air and this top layer shrinks a little.
If you add a Thinner or Medium to paint, then that thinned paint will dry quicker than the fat oily paint as the medium evaporates off.
The Fat over Lean golden rule is applied when we are painting a painting over a period of time. We add Thinner or Medium to the bottom layers so that they dry fast. As we work up the layers we gradually add less medium to the paint, so that the oil content of the paint is gradually increased.
If we were to reverse the Fat over Lean rule, the top (thin) layers would dry before the (fat) bottom layers and the surface would crack.
The exception to the rule
There’s always one!
When painting Alla Prima there is no need for the Fat over Lean rule as the painting is done in one sitting. I can explain later about Alla Prima in another email, as that’s how I work.
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