Fat Over Lean Rule

The fat over lean  rule for oil painting  is  the principle that you apply a layer of paint with a higher ratio of oil over a layer of paint with a lower ratio of oil. The layer with more oil, the fat layer, is more flexible and less prone to cracking. This article provides recipes for lean and fat mediums for oil painting. 

By Jim Hingst @hingst_jim

A fat paint has a high ratio of oil binder to pigment. Paint right out of the tube is generally considered fat. By adding more of an oil medium to it, you will make it fatter. While you can use commercial mediums such as Liquin, traditional mediums are typically comprised of equal amounts of stand oil and Damar varnish, which are thinned with pure gum turpentine. The amount of Damar Varnish should never exceed the amount of oil used.   The amount of turpentine, however,  used can vary. Ratios of oil: varnish: turpentine can be 1:1:7 to 1:1:3.

 Lean Medium 

(1:1:7 ratio – use for Imprimatura:Toning the Substrate)

·         1 part stand oil

·         1 part Damar varnish

·         5 parts pure gum turpentine

Lean Medium 

(1:1:5 ratio – use for underpainting)

·         1 part stand oil

·         1 part Damar varnish

·         5 parts pure gum turpentine

Fat Medium 

(1:1:3 ratio – use for top or final layers of the painting)

·         1 part stand oil

·         1 part Damar varnish

·         3 parts pure gum turpentine

Stand oil, if you have never heard the term, is linseed oil, which has been heated in the absence of oxygen. It is very viscous, having the consistency of molasses. Unlike other types of linseed oil which are prone to yellowing, stand oil maintains its clarity. Damar varnish is added to the stand oil to reduce its viscosity. (Damar  varnish recipe.) The percentage of turpentine used varies. The less used, the fatter the mixture.

The fatter that the paint is, the more flexible it is.  That’s a good thing. The more flexible paint should last longer. The downside is that the fatter the paint is, the longer it takes to dry.

Lean paint, on the other hand, has a lower amount of oil to pigment. You can make  paint leaner by adding pure gum turpentine to it. When doing this, easy does it. Limit the amount of turpentine to no more than 25%. Here’s why. Thinning paint too much, which reduces the percentage of its binder, can cause a failure of the paint to bond to the substrate. It can also result in an intercoat adhesion failure, in which one layer of paint separates from another.

As the oil content of paint decreases, it dries faster.  The paint also becomes more brittle or inflexible. That in itself is not a problem. Painters have used thinned paint to tone their canvases or for their underpaintings. Problems occur when a lean paint layer covers a fat one. The reason is that as the underlying flexible layer of fat paint expands and contracts, the overlaying layer of inflexible lean paint cannot move at the same rate. The result is that the lean layer cracks.

To prevent cracking paint, you should follow the fat over lean rule. Another preventative measure is to paint wet on wet (or what is referred to as “alla prima” painting). In making a paint fatter, artists will use medium in one of two ways. One popular method is to brush the medium directly onto the canvas and paint over it. Another method is, after arranging the colors on you palette, to add a drop or two of the medium to each color. This method is arguably a better way of controlling the amount of medium added to your paint.

About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.

Slides of Jim's Artwork

© 2015 Jim Hingst