R U L E S T O O I L P A I N T I N G :
Unlike other media with drawing or acrylic painting, oil painting does in fact have rules.
The most complicated part of learning oil painting is truly understanding the 3 rules:
1- Fat Over Lean
2- Thick Over Thin
3-Slow drying over fast drying.
Once you understand these rules there are ways to technically break them, but they still adhere to the principals of oil painting and it’s limitations in proper application. Now even though there are these “limitations”, once you understand them and can manipulate them to your process, oil painting opens up a whole new realm of possibilities and techniques that acrylic painting can’t stand up to. It makes it an incredibly versatile medium once you get it.
I’m going to break down the 3 rules that may seem complicated when reading, but will make more sense as you begin to experiment and understand oils more and more. Once I’ve explained them, I’m going to show you ways to break these rules!
There are two oil painting techniques that don’t require you to follow these rules ( oil dry brush, and alla prima) however when dealing with traditional oil paint application techniques , a composition is usually built up using different layers of colour. For example, if you are painting a portrait, you may start with an area of background colour, on top of this you may sketch out the proportions of the portrait with another colour, and on top of that you may add further colours for the detail, and add glaze layers for value or tonal corrections or to enhance the vibrancy and depth of the painting. The way each of these layers of colour interacts with each other is important and will affect how your finished work looks.
If you want to make the most of your painting, there are three tried and tested rules that will serve you well:
Fat Over Lean
Each successive layer needs to be more flexible than the one underneath. This can be done by adding specific mediums to each successive layer, which makes each new layer more flexible than the previous one and stops the painting from cracking. Another way to think of the rule is ‘Flexible over Non-Flexible.’
There are mediums help create this flexibility within layers without having to get too fatty (such as Winsor & Newton’s Liquin Fine Detail and Liquin Original, as well as Gamblins Galkyd and Galkyd Lite) . By using them, there is no need to keep on adding oil/fats to your colour.
Thick Over Thin
When painting with heavy colour, it is best to apply thick layers over thin layers, this is because the thin layers dry quicker. For example if you like the impasto style of the Impressionists with their textured and thick bold brush strokes then it is important to remember that these thick layers need to be upper most – as thin layers on top of impasto layers are likely to crack.
Slow Drying Over Fast Drying
It is best to use fast drying colours continuously as under layers. If a fast drying layer is applied on top of a slow drying layer then your painting may crack. This is because the fast drying layers will have dried on top of layers that are still in the process of drying out, and as the slow drying layers dry, they will pull and twist those (fast drying) layers above causing them to crack.
All right, now you know what the rules are, you may be asking what the hell is a fat and what is a lean?
To understand this requires you to understand what oil paint actually is. So as the name suggests, oil paint is pigments (in powdered form as any other pigment) that is then mixed with an oil as a binder. This oil is also called a “Fat”. When you mix the oils and the pigment together you get oil paint. The oil that is most commonly used for this is linseed oil (But there are a range of fats out there). When you open a new tube of oil paint, you may see a little runny fluid drip out... this is the oil!
Now if you’ve ever left oil of any sort out, you’ll then know it doesn’t exactly dry up. So this is why oils are notorious for being a slow drying and difficult medium. So in order for your piece to dry you need some sort of paint thinner/ solvent also called a “lean”. These thinners break down the oils and allow the paint to dry, but in doing so it then breaks down the paint to being closer to its pigment form... essentially bring it back to its dusty flaky pigment. So you never want to use too much thinner ... but you also don’t want to use just oils (Or it will never dry) and you don’t want to use just a thinner since it ruins the integrity of the paint, and be prone to flaking and cracking, lose its flexibility and stop you from getting the most of oil painting.
So you will want to make sure that you use both fats and leans for your painting.
Understanding how to use each and when can be tricky to start, which is why these rules are helpful to remember. A lean/solvent/thinner will break down your oils/fats so if you use a lean over a fat, it breaks it down and causes it to be fragile and can crack. So this is why people will use a lean (Like turps, mineral spirits, or OMS) for their under paintings only.
This is how it’s been done for centuries, but I’m not a fan of using anything that degrades the paint especially as a base for all the next layers to rest upon (those are all also toxic and I don’t want to fuck with that), so I have a different approach.
This approach is also what helps me break the rules of oil painting.
By eliminating the leanest of leans, it makes it easier to follow the fat over lean rule.
What I do instead is use only one medium which is both a fat and a lean. (My choice for this is either Galkyd or Galkyd Lite or Liquin or Liquin Fine Detail. You can read more about them in my SUPPLIES tab).
So then all I have to do is be mindful of the other two rules.
They are easily mitigated by working in many thin layers, that always use the medium, and as I get to my final layers, add more of my medium until it becomes a translucent glaze layer with very little paint.
So instead of adding details at the end, I work them into my mid layers... slowly adding details with each layer and building them up. This gives a great depth to the work, instead of having all your details sit flat on top.
The more fats and leans you decide to work with the more aware you will have to be to make sure all your leans are in your early layers and your fats in the later. But then you’re left with some slow drying last layers. So by working with a single medium that can act as both, you don’t have to abide by the same rules or time restraints as the traditional technique.
The biggest thing to note with my technique is that if you decide to do some glaze layers, you cannot go back and rework it. Once those translucent glaze layers are on, it makes the painting super slippery, and oils without being heavily diluted with the medium won’t stick to it very well. If you’re someone that likes to rework, then the traditional approach may be beneficial. Keep in mind though that this technique does allow you to adjust tones and values quickly without having to repaint whole sections. Though the amount you can adjust is limited to only going darker in value or tonal shifts that work with the colour you’re correcting. If this doesn’t make sense, you’ll want to check out my GLAZING tab.