Fat Over Lean

Ever heard the phrase “fat over lean” in oil painting and wondered what it actually means or why it’s such a big deal? Katie Liddiard takes the mystery out of this time-tested rule and shows you exactly how it can keep your paintings vibrant, stable, and beautiful for generations. With clear explanations and easy-to-follow demos, she’ll help you see how a simple shift in how you layer your paints can make all the difference in both the look and the longevity of your work.

Katie begins by explaining that “fat” refers to the oil content in your paint or medium, while “lean” means a lower oil content. The reason this matters is simple: too much oil in the wrong layer can cause paintings to yellow, crack, or even weep oil over time. By following the fat-over-lean rule, you’re building a paint film that can last for generations.

With side-by-side demonstrations, Katie shows the difference between thin, lean underlayers (using just mineral spirits or a lean medium) and richer, more oil-heavy top layers (using a fat medium with linseed oil). She also shares how to decide when to add medium at all—and why sometimes straight paint is the best choice.

You’ll see exactly how different mediums behave: lean mediums glide thinly and break down pigment for looser coverage, while fat mediums create a smooth, flowing glaze perfect for final details. Katie also explains how pigment choice affects oil content, why she avoids overly oily colors, and what alternatives she reaches for without long-term stability issues.

By the end of the lesson, you’ll know how to structure your layers for durability, control your paint’s handling qualities, and make informed choices about pigments and mediums. Whether you’re just starting out or refining your professional technique, Katie’s clear explanations and practical tips will help you paint with confidence—and ensure your work stands the test of time.