How should oil medium be mixed in the initial layers of an oil painting according to "fat over lean" principle?

In the context of oil painting, the "fat over lean" principle is crucial for ensuring the durability and flexibility of the painting over time. This principle dictates that the initial layers of paint, often referred to as the "lean" layers, should contain less oil than the subsequent layers. This approach allows the lean layers to dry more quickly and provides an appropriate foundation for the thicker, more flexible layers that follow.

When oil medium is mixed with less oil in the initial layers, it dries faster and shrinks less, which is important because if the upper layers (which contain more oil) were applied over lean layers that didn't adhere well, it could lead to problems such as cracking or peeling. By adhering to this principle, artists create a stable structure where the more flexible paint layers can expand and contract without compromising the integrity of the underlayers.

This understanding reinforces the practice of ensuring that the initial layers remain lean to build a solid base that supports the richness and complexity that the later, "fat" layers will bring to the painting.