Oil Painting Fat Over Lean, As Easy As 1,2,3

By Rebekah Griffith, 9.10.2020

After graduating with a BFA in Painting at Western State University  2016, I felt like I knew very little about the properties and techniques of oil painting.  The Aristotle quote “The more you know, the more you realize you don’t know” hit hard.  A feeling of being sickeningly overwhelmed by lack of knowledge slapped me in the face and propelled me to research the nitty-gritty details of oil painting including the “fat over lean” concept.  Fat over lean is the ratio of medium to solvent that you use to thin oil paint.  The type of medium or solvent used is frequently discussed among artists, but the ratios used is not something often talked about.  As part of my quest for answers I reached out to the company, Gamblin, that makes oil paint, and peppered them with questions.  Gamblin patiently answered my maze of questions, leaving me with pages and pages of answers.  The subject of fat over lean can be very overwhelming and hard to understand.  In doing my research, I concluded with an easy three step method to ensure oil paintings would hold true to the fat over lean concept.

What is Fat Over Lean?

The binder in oil paint is…oil, surprise! Oil is a fat.  Traditionally, oil paint is used in conjunction with a “medium” something to thin the paint for underpaintings, general application, or final glazing.  All oil painting mediums, such as refined linseed oil, stand oil, poppy oil, safflower oil, and walnut oil are 100% fat.  Refined linseed oil is the medium I use because it is affordable and dries relatively fast.  If a fat, like refined linseed oil, is used alone to thin paint, you would be waiting weeks for the paint to dry. No thank you.  Here is where solvents come in.  You have probably heard of turpentine, that super smelly nauseating chemical.  Turpentine is a solvent, solvents are considered lean.  The purpose of solvents are to “cut” or thin down the paint, more so than an oil medium can, and significantly increase the dry time.  I have never painted with turpentine because of the harsh chemical properties.  Extra Mild Citrus Thinner from Eco-House is what I use as a solvent for my paint; it is affordable and considerably less toxic.  Mixing a fat and a solvent together is an ideal situation if you are using a medium to paint.  When using a pure solvent it creates unstable and inflexible paintings layers that are much more likely to crack considerably over time.  Solvents should always be mixed with a fat medium.

 The idea of painting fat over lean is to have the first layer of paint the highest in solvent (lean) and the proceeding layers gradually decrease in solvent and increase in oil (fat).  Thus creating layers of paint that are fat over lean.

Why is Fat Over Lean Important?

The oil painting process fat over lean only applies to layered oil paintings.  Paintings that are created in a true alla prima style, that is to say completed in one day, only have one layer of paint film.  Even if an alla prima painter applied multiple layers in one sitting, those layers would meld together and dry as one paint film.  Alla prima paintings, and paintings that use paint directly out of the tube with no medium, are considered the most stable, and the least likely to crack over time.  Paintings that use the highest amount of solvent or oil medium are the least stable, the most susceptible to cracking.  If you do choose to use a medium, use it minimally!  

Oil paint is most likely to crack over time if the layers of paint are lean over fat instead of fat over lean. 

Painting fat over lean increases the archival quality of the painting.  If you have spent time in an art store you have probably noticed the word “archival” slapped onto paper, canvases, tape etc.  Archival refers to the lifespan and quality of life of the work of art.  Harsh chemicals or acids in art materials have the potential to harm the artwork over time or increase the rate of aging; an “archival” drawing paper is free of such acids or chemicals.  There are some artists that go crazy over the idea of archival quality, obsessing over the thought of their paintings living hundreds of years beyond their death in perfect condition.  Other painters like, Nicolás Uribe, could care less what their paintings look like after they die.  I fall in between these extremes.  When painting I do not want to quench my creativity and be frozen in fear thinking about the possibility of my painting cracking in 50 years if I do not use the correct ratio of medium to solvent.  Painting layers that are created with a medium (remember the most stable layers are those that use paint straight out of the tube with no medium) are the most stable when they have a good balance of both a solvent and a medium.  I also do not want to mix a puddle of medium and solvent for each painting sitting and hope that by chance I am achieving the correct ratios.  However, the fat over lean concept can not come in between the flow and creativity of painting.  I have developed a very easy way to ensure layered oil paintings are fat over lean without it hindering the creative process.

 Easy as 1,2,3,

Typically, I paint in three main layers.  A thin underpainting, the block in stage, and final details.  The first two stages usually take one sitting each, and the last stage can take its time over multiple sittings.  Old baby food jars are what I use to store pre-mixed solvent and oil medium.  When I was first learning oil painting I purchased one of those seemingly nifty metal oil wells that clipped onto your palette; the opening allowed for small brushes only which was impossible when wanting to cover large areas during the underpainting stage.  The baby food jars allow for small to large brushes to dip in.  I keep on hand three jars that are labeled 1, 2,3,  for each distinct painting layer.  The jars are stored in my studio mini fridge to prevent the oil from rotting over time.  When it is time to paint I grab the jar with the number on it that corresponds with the painting layer I am about to tackle.

Medium Recipes: 

1. For the first layer, mark a  jar with a number “1” and fill with  ¾ solvent and ¼ oil
2. For the second layer or sitting, mark a jar with the number “2”  and fill with 1/2  solvent and 1/2 oil 
3. For the last layers mark a jar with the  number “3” and fill with  ¼ solvent and ¾ oil

The measurements are approximations, again I personally do not want to get too caught up in the archival vortex where it threatens to hinder creativity.  Depending on what solvent and oil you choose to use, you may end up tweaking the ratios.  

What tips have you found helpful to paint “fat over lean?

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