Essential Guide to Painting Materials and The "Fat Over Lean" Rule

Introduction: The Physicality of Art

Hello, I want to start with the basics, with the foundations. It's the first letter of the painting alphabet; it's what determines whether a painting, in any style or format, will live the longest in good condition, or inevitably deteriorate and self-destruct months or years after being painted.

We don't work with words or sounds: our materials are very physical and very chemical. Although it may sound grandiose, we must understand the capabilities of our materials, just as a good baker or a good carpenter does with theirs.

We'll talk about supports or brushes another time: today we'll briefly discuss the colours we paint with.

The First Golden Rule: Two Families of Materials

You must always remember this, as it is the foundation for the future construction of all painting. There are two primary categories:

1. Fat Materials (Oil-Based)

Fatty materials are those that are diluted with solvents and mixed with oils, varnishes, and thinners.

• Oil Paint: The great champion of Western painting from the Renaissance to the present day.
• Oil Pastels: Crayons made of beeswax or synthetic wax.
• Encaustic: An almost extinct technique involving a heated metal palette knife where pigments are mixed with melted beeswax. These coloured impastos are applied to the canvas or wooden panel with spatulas or brushes. Finally, instead of a final varnish, the painting is rubbed with a wool cloth to bring out the natural lustre of the wax.
• Enamel (Industrial) Paint: High resistance and great adhesion. Artists appreciate its durability and smooth finishes. It is sold in litre or gallon containers rather than tubes.
  The appearance and use of industrial materials by artists opened new horizons. Enamel paint is composed of resins, oils, or varnishes. It was created to protect wood, metal, or tiles from exposure to moisture, wear, or weathering. It is suitable for large surfaces.
• Bituminous Paint: These paints are created as extreme protection against corrosion and moisture, so the pigments make up a small percentage. Not suitable for painting. These are created for extreme protection against corrosion; pigments make up a small percentage and do not react well to mixtures.
  

2. Lean Materials (Water-Based)

Lean materials are those that are diluted with water and mixed with water.

• Tempera (or Temple): One of the oldest and most durable techniques, using egg yolk, casein, or vegetable gums as binders. It features fast drying and a matte finish. It was the main medium of European painting before oil (until 1500) and is characterized by fast drying, vibrant colours, and a matte finish.
• Watercolour: Pigments bound with gum Arabic. It achieved great popularity in Europe in the 18th and 19th centuries. In the Far East, it was the traditional technique in combination with ink.
• Inks: Ink is a colloidal emulsion. Traditionally, black ink was based on burnt organic material, soot collected from the fumes produced by the combustion of resinous materials, called carbon black, dissolved in water.

Ink (called Chinese or India ink depending on the language) is an ink used mainly in Chinese, Japanese, and Korean calligraphy (in Japan, it is called sumi-e). It was used to create monochromatic paintings in diluted ink (wash), which were deeply influenced by Chinese culture and propagated by Zen monks, precursors of the Japanese sumi-e technique. 

An ancient technique, ink was used in Ancient Egypt to write and draw on papyrus from the 26th century BC, and Chinese inks can be traced back 3,000 to 4,000 years to the Chinese Neolithic period.

• Alkyd colours: After WWII, in the search for faster-drying alternatives to oil paint, alkyd colours appeared, which were the predecessors of acrylic paints.
• Acrylic Paints: They are fast-drying colours, composed of pigments suspended in an acrylic polymer emulsion. Acrylic paints are water-soluble when applied, but become water-resistant and permanent when dry. They are notable for their versatility, allowing finishes similar to watercolour, gouache, or oil paint. One of their advantages is that they don't require solvents like turpentine spirits, which have a strong odour and can sometimes irritate the skin; only water is needed.

Chemically, when the polymer emulsion dries and hardens (and it does so quickly, unlike oil paint), a second coat can be applied.

• Latex Paint: The water-based industrial version, equivalent to enamel paint. Being water-based, it has a low odour. It has excellent adhesion, as it was created for both interior and exterior walls.

The Science of Emulsions

An emulsion is a mixture of liquids that "repel" each other, such as water and oil. Let's pause for a moment to understand this: some liquids dissolve in others (glycerine in water, for example). This phenomenon is chemically called dispersion. But by applying various forces, I can "force" these antagonistic materials to mix.

For example, I put water and oil in a blender, and using its centrifugal force, I force them to mix as two liquids into one. This result will be an emulsion that, after prolonged rest, will separate again. This is why, before use, you have to shake the ink, just like vaccines and other things whose medium is an emulsion.

The Case of Water-Soluble Oils: An "Anomaly"

By definition, materials are divided into water-based and oil-based. But research and advancements have led to the invention of water-soluble oil paints. This sounds like nonsense, contrary to everything we've discussed, but it's a very special emulsion.

First of all, why? Who needs it? Well, in painting education, academies can't fail to teach the great classical technique of oil painting. When municipal safety inspectors came to check the facilities and discovered garbage containers full of rags soaked in paint and solvents (for cleaning brushes and spatulas), which are flammable materials, they ordered the prohibition of solvent use under penalty of closing the institution.

Not teaching oil painting or only teaching acrylics would drive many students to private oil painting lessons. This is how the industry began searching for "oil paints without oil solvents." Here we return to the topic of EMULSIONS.

All painting materials require binding with oils, binders, or waxes that darken or yellow the pigments (that is, they do not oxidize in contact with the pigments). All plants possess essential oils, and while not all are edible, very few do not oxidize in contact with pigments, such as linseed oil, poppy oil, etc. In this select list, they found safflower oil, which allows for easier manipulation of its molecular structure to accept water.

As a result, about three decades ago, water-based oil paints emerged, without strong and flammable solvents like white spirit. In response to demand, all the major oil paint companies created their own lines of water-based oils.

Twenty-five years ago, my retired students would return from trips to Europe and the USA with sets of these paints. They appear creamy and similar to oil paint, but when they asked my opinion, I said the same thing I say today: we'll have to see paintings done with these materials in 50 or 100 years. Perhaps they'll be as good as the original oil paints or even better, but perhaps all sorts of problems and deterioration will begin.

It's like when they created genetically modified wheat: total euphoria, because instead of one harvest, there would be two per year. Soon after, the number of people with celiac disease, who can't break down gluten in their bodies, skyrocketed.

Therefore, it's something I neither criticize nor celebrate: those who aren't interested in the longevity of their work should take risks. I prefer, and recommend, using safe, non-experimental methods with centuries of experience regarding their behaviour and performance.

The Second Golden Rule: Fat Over Lean

The final longevity of your work depends on the order of your layers.

Why Order Matters

If this order is reversed—first oil and then acrylic—the painting is doomed to self-destruct. It may look fine at first, but after a few years, it will darken and crack. This destruction is irreversible and impossible to stop. If you wish to preserve your artwork, you can refer to the detailed guidelines on the structure and preservation of paintings from the Canadian Institute of Conservation (CCI).

Enough chemistry for today; just know that's how it happens.

Every painter who wants to be a professional should always remember the two main families of materials and the golden rule of FAT OVER LEAN.

That's enough for today; we'll meet again next time.

Have a fruitful and creative day.