It´s common to hear at painting studios about the fat over lean rule. This is the first rule a beginner learn from his teacher when painting in oils. Although most painters works through a direct approach painting the whole work into a single session, sometimes we need a number of stages of sessions, composing the work in a layered manner. That said, it´s important to understand that, when we paint alla prima, the fat over lean rule is not important, but when we use different stages, in an indirect way, it´s safer to stick to the rule.
It´s very easy to understand the rule: when you add medium to your paint like vegetable oil, you got fat paint. The less oily the paint gets, like when the paint is used directly from the tube without adition of medium or when it´s mixed to a solvent (like turpentine), you got a leaner paint. If the rule is fat over lean, that means the artist should paint with leaner paint first and with fat paint afterwards. That means leaner paint on the bottom and fat on the top: fat over lean.
Working Method
One way of using the fat over lean rule is to start your painting using some solvent, like turpentine, into your paint. You can dip your brush into the container of solvent and mix the paint with the turpentine. This way, your first layer will be painted with a leaner mixture, because its mixed with the turpentine. Into the next stage or layer, paint with oil paint direct from the tube, without any additions. In the next layer, work your paint adding some vegetable oil, like linseed oil, into your paint. This way, into each layer there is a higher concentration of oil, making each layer more oily, following the rule of fat over lean.
Another way of using the fat over lean is to have pre-mixed mediums, ready to use on containers, adding them on different stages on your work. You can make three different mediums with different proportions of linseed oil and turpentine.
The first medium, the leaner one, might be just turpentine or turpentine with a small amount of linseed oil. Second medium might be 50% turpentine and 50% linseed oil. The third and more oily medium be pure linseed oil or 1/3 turpentine and 2/3 linseed oil. Keep in mind these numbers and proportions are just an example and may be adjusted to your own taste and needs. The only important rule is to make a progression from an leaner mixture to an oily one. It´s good practice to always use the same amount of medium in each layer, so try to dip your brush into the mediums and mix it always using the same amount of medium and paint, so there is always the same ratio on every layer.
Simplier Way
The use of pre-mixed mediums for each stage of the paint might be a problem if you use too many layers, resulting into an complex and unpractical way of working. Dont overthink the problem, keep it simple. First of all, the fat over lean rule was created to make sure begginers respects the drying time of each layer. When you add oil to your paint the fat content makes the drying time much longer, this way layers on top (more fat) dries slower than under layers (leaner), a smart and easy way to be sure no crack, fissures or craquelures appears on upper layers. With this in mind, let´s put the fat over lean aside for now and think differently.
Two variables play an important rule here: drying time and paint thickness (or quantity), both directly related. If there is many layers into an painting and if the top layers are drying faster than the bottom layers, the bottom layers will have more time to expand, to move, during the drying process, resulting on cracking the upper layers. This way, it´s really important to respect the drying time between layers.
It´s very easy to understand the rule: when you add medium to your paint like vegetable oil, you got fat paint. The less oily the paint gets, like when the paint is used directly from the tube without adition of medium or when it´s mixed to a solvent (like turpentine), you got a leaner paint. If the rule is fat over lean, that means the artist should paint with leaner paint first and with fat paint afterwards. That means leaner paint on the bottom and fat on the top: fat over lean.
Working Method
One way of using the fat over lean rule is to start your painting using some solvent, like turpentine, into your paint. You can dip your brush into the container of solvent and mix the paint with the turpentine. This way, your first layer will be painted with a leaner mixture, because its mixed with the turpentine. Into the next stage or layer, paint with oil paint direct from the tube, without any additions. In the next layer, work your paint adding some vegetable oil, like linseed oil, into your paint. This way, into each layer there is a higher concentration of oil, making each layer more oily, following the rule of fat over lean.
Another way of using the fat over lean is to have pre-mixed mediums, ready to use on containers, adding them on different stages on your work. You can make three different mediums with different proportions of linseed oil and turpentine.
The first medium, the leaner one, might be just turpentine or turpentine with a small amount of linseed oil. Second medium might be 50% turpentine and 50% linseed oil. The third and more oily medium be pure linseed oil or 1/3 turpentine and 2/3 linseed oil. Keep in mind these numbers and proportions are just an example and may be adjusted to your own taste and needs. The only important rule is to make a progression from an leaner mixture to an oily one. It´s good practice to always use the same amount of medium in each layer, so try to dip your brush into the mediums and mix it always using the same amount of medium and paint, so there is always the same ratio on every layer.
Simplier Way
The use of pre-mixed mediums for each stage of the paint might be a problem if you use too many layers, resulting into an complex and unpractical way of working. Dont overthink the problem, keep it simple. First of all, the fat over lean rule was created to make sure begginers respects the drying time of each layer. When you add oil to your paint the fat content makes the drying time much longer, this way layers on top (more fat) dries slower than under layers (leaner), a smart and easy way to be sure no crack, fissures or craquelures appears on upper layers. With this in mind, let´s put the fat over lean aside for now and think differently.
Two variables play an important rule here: drying time and paint thickness (or quantity), both directly related. If there is many layers into an painting and if the top layers are drying faster than the bottom layers, the bottom layers will have more time to expand, to move, during the drying process, resulting on cracking the upper layers. This way, it´s really important to respect the drying time between layers.
It´s simple and uncomplicated. If you work with layers, just make sure to wait till everything is truly dried before starting another layer: if your first layers are completely dried, there is no need to apply any medium to your paint, as long everything is dried. That means to sometimes wait more than a week depending on the pigment used on the area. The weather and humidity might also extend or diminish drying time. If you cant wait, the solution is to use dryers or in a more practical way, working alla prima and not through layers. A common strategy to gain time when painting in layers, without using dryers, is to paint different canvases at the same time alterning between works.
 |
| Painting by Lucian Freud: Heavy impasto drying slowly |
Some artists paint very thinly, using their brushes with little paint, creating a very thin film on the final painting. Other artistas use much more painting, loading their brushes much more, creating the famous impasto effect, leaving a lot of texture on the surface. The quantity of paint used and thickness of the paint will alter the drying time. The more paint we use, the longer it will take to dry, truly loaded layers of paint take years to get fully dried, while thinner layers will take much less, usually dried within a few days.
That is why drying time and thickness can make the fat over lean rule even more difficult to understand. To make it everything safer, keep in mind to always paint with thin layers first and if you must create more thick layers, make sure they come later, that is, on the top. First layers must be thinner and later layers must have more paint.
There is a third variable that must be considered. Some pigments dry faster or slower than others. So, when working in stages or layers, you must consider not only the amount of fat on your medium, the thickness and order of your layers but also, the particular drying time of each color used. If you build an entire layer made with burnt umber, tha drying time will be much faster than if you build an entire layer containing cadmium colors. So, it´s logical to use fast drying colors on the first layers and slow drying colors on the top layers.
Remember that everything turns more complicated when there is too many layers, if you paint alla prima or with just a few layers, lets say two or three, everything is simplier and safer. Ultimately, when working with different stages, the important thing is to have patience and wait for the last layer to be fully dried, and not half-dried or dried just to the touch, before advancing for the next one. You might want to be on the safer side and make sure everything dries proprerly adding one or two drops of some drier and ensure to keep the drying time shorter. This is specially useful on the bottom layers so you can move to the final layers sooner.
For final thoughts, always remember the following:
- Avoid work with too many layers. If you must use different stages, use at the most, three or four.
- Lean mediums on the first layers and with fatter mediums later.
- Thinner layers first and thicker layers later.
- Fast drying colors first, slow drying colors later.
- Respect the drying time of each layer.
THOMPSON, Daniel V. The Materials and Techniques of Medieval Painting; Dover; New York.
LAURIE; A.P.; The Painter´s Method´s and Materials; Dover; 1967.
DELAMARE; Guineau; Colors: The Story of Dyes and Pigments; Harry Abrams; 2000.
MAYER; Ralph; Manual do Artista; Martins Fontes; 1950; 1957 e 1970.
EASTLAKE; Sir Charles Lock; Methods and Materials of Painting of the Great Schools and Masters; Dover; 1847
