Fat-over-lean (oils)

Oil Painting

Fat-Over-Lean

The “fat over lean” rule allows you to build a painting that is flexible so over time there will be less cracking to your painting.

Here is my suggestion:

· 1^st layer(s): 1:1 Galkyd to Gamsol

· 2^nd layer(s): 2:1 Galkyd to Gamsol

· 3^rd layer(s): 3:1 Galkyd to Gamsol

· 4^th layer(s): 1:0 Galkyd to Gamsol (straight Galkyd)

· Final Glaze Layer(s): Galkyd with additional 10% Stand Oil

Below is a chart detailing the fat content of the Gamblin painting mediums:

Gamblin Medium:	Fat %
Linseed oil, Stand oil, Poppy oil	100%
Galkyd	55%
Neo Megilp	55%
Galkyd Gel	50%
Galkyd Lite	50%
Galkyd Slow Dry	40%
Gamsol, Cold Wax Medium	0%

Keep in mind that this is ONLY a guideline to ensure the permanency of your oil paintings. Try to keep it in the back of your mind, but don’t let it control your process. What should be avoided are drastic shifts from “fat” layers to “lean” layers. Also, keep this in mind: THE SIMPER THE PAINTING, THE MORE PERMANENT IT WILL BE.

The under layers of a painting should be leaner than the upper layers. There are two different ways that painters use painting mediums. The first method entails using the same ratio of painting medium to oil paint throughout the painting structure. In this case, the painting medium must be modified to control its fat content. In the initial layers of the painting, the medium should contain more solvent and less binder. As you add layers, increase the binder (example: linseed oil) until the upper layers contain the reverse of the under layers. This means the top layers will have little solvent and more painting medium.

The second approach is to use varying amounts of the same painting medium when building up paint layers. All oil painting mediums are fat. When you add medium to oil paint, the oil content increases. In the initial layers of the painting, add a minimal amount of painting medium; then increase the amount of painting medium as you build up paint layers. Once medium is added to colors, the differences in oil content among the different families and hues of oil paints is negligible.

To determine the oil content of a color, look at the paint. The shinier the paint, the fatter it is. For example, Napthol Red is shinier than Cadmium Red, so Napthol Red has a higher oil content.

Here's a diagram of the "Fat over Lean" principle:

Same ratio Medium to Oil paint Varying Amounts of Medium

Varnish
Glaze

1:0 Medium : Solvent Most Medium
Paint layer
3:1 Medium : Solvent More Medium
Paint layer
1:1 Medium : Solvent Less Medium
Paint layer

Ground
Size
Support
Fabric Panel

Hi Aaron,

I’ll try to answer all your questions from the two emails.

What about Alla Prima method where the painting is started and finished

the same day? Does it matter? What would be best in that case?

Starting and finishing a painting in one painting session is, in fact, the best way to create a permanent painting. All of the paint dries as one homogenous paint layer. This is the simplest of painting structures. However, this is not conducive to fit the intensions and styles of every painter. Therefore, the “fat over lean” principle comes into greater importance when painters work in multiple layers over multiple painting sessions.

For Plein air work I just bring Gamsol because it travels well- is that advisable?

I don't usually thin it too much, but sometimes.

The main function of a solvent is to break down and dissolve the linseed oil binder of the oil color. When solvent is added alone, it reduces the amount of flexibility of paint layers as they dry. This may make the paint film more prone to cracking. Adding excessive amounts of solvent to oil colors prohibits the paint from making a permanent, cohesive paint film. I would recommend one part Gamsol and one part Galkyd. This will make a medium that has a very low viscosity, which will make oil colors very fluid. You can add as much of this medium to your oil colors without adversely affecting the permanence of the paint film.

Also, I was a little confused about when the same amount of painting

mediums is added to a color from beginning to end. It sounds a little

easier to understand, no? Are you advising against that approach? What

would be the recommended mixture for that?

In the “fat over lean” brochure that I attached (let me know if you didn’t receive this), it outlines two ways to maintain the “fat over lean” principle. This is entirely dependant on how the painter works – there is no right or wrong here. The first approach is when adding, roughly, the same amount of painting medium from start to finish. The fat content of the painting medium should be modified to maintain the movement from “lean” to “fat”. Simply put, this can be achieved by adding a mixture of solvent and medium in the under layers, and reducing the amount of solvent with each subsequent layer so that on the top layers, straight painting medium is added. The other approach is when varying amounts of painting medium to each layer. Oil colors = “lean” and painting mediums = “fat”. In this approach, use little to no painting medium in the under layers, and add an increasing amount of painting medium to oil colors with each subsequent layer.

The “fat over lean” principle is primarily about flexibility. It can also be described as “flexible over less flexible”. Painting mediums, and especially alkyd-based painting mediums, increase the flexibility of paint layers, hence them equaling “fat”.

I don't really know what you mean when you say that? How can I keep it a

simple approach, and still paint for several days on it? What does it

mean to be simple?

I’ll be the first to admit that it’s easy to get caught up over all of this. It’s probably healthy to leave some of this info at the studio door as to not let it control your painting process. After all, painting is not “laying pipe”! However, it is a guideline to help artists build permanent paintings. Keep this in mind as you are developing the underpainting, as this is the foundation to your painting. Also, try not to add too much straight Galkyd, for example, to your oil colors too soon in the painting structure, as this constitutes a “fat” layer. Like I mentioned in my earlier email, try to avoid drastic changes from “fat” to “lean”.

I would love to simplify what sounds very complex, but I don't quite

understand it well enough...Part of the problem also is, do we need to

consider the fat content that is already in the paint? For example,

black? I have been told that, if you paint over it it will crack or

sag or otherwise be very bad.... How do you think about the individual

colors when considering the fat content of the oils you are adding? Can

you get by without thinking about them much?

ONCE PAINTING MEDIUM IS ADDED TO OIL COLORS, THIS MAKES THE DIFFERENCES IN OIL CONTENT AMONG OIL COLORS NEGLIGIBLE.

Please let me know if you have any additional questions. Thank you for choosing our materials.

Sincerely,

Scott

Aaron Holland Fine Arts

Site Menu

Fat-over-lean (oils)