Like traditional, water-mixable, or water-soluble oil paints, these are made entirely from oils that can be thinned with solvents such as white spirit and turpentine.However, their formula has been modified in such a way that these toxic thinners are actually unnecessary, having been completely replaced by water.
In order for the paint to be diluted with water, it is formulated as an emulsion — a stable mixture of microscopic oil droplets in water. This also has the advantage of allowing it to dry much more quickly.
Dilution
By adding a little paint to a lot of water, you can easily achieve a very transparent color.
In other cases, when we want to achieve a thicker consistency, we must first “activate” the emulsion. A homogeneous mixture isn’t achieved by simply adding a lot of water to the paint, but by mixing the two gradually, little by little, using a wet brush.
If you apply pure paint to a very thin, i.e., too wet, layer, it will simply run down onto the underlying layer. This is because an emulsion between the oil paint and the water has not formed sufficiently; the water must first be allowed to evaporate.
Some colors lighten when diluted, which is a characteristic and inevitable property of emulsions. Once the water has evaporated, the original color returns.
Oil paints, whether traditional or water-soluble (such as Royal Talens’ Cobra), are the most challenging to use in terms of the painting’s longevity.
Generally speaking, every oil painting consists of:
- preparation of the base
- paint application
- and varnishing.
The Foundation
The quality of the preliminary preparation is of great importance for the longevity of the painting. The painting surface can vary widely— cardboard, wood, cotton, or linen—but it must be properly prepared beforehand. A poorly treated surface absorbs the oil from the paint and is eventually corroded by it. The oil content in the paint must be sufficient to completely cover the dry pigments, forming a durable layer. Only then will they remain firmly bonded over time, without cracking.
Surfaces can be primed with gesso, and highly absorbent substrates can first be sealed with pure, colorless acrylic, such as Amsterdam Acrylic Binder. After that, , the gesso is applied in two thin, cross-hatched layers. Canvases stretched on a stretcher or frame canvases and primed surfaces arrive ready for use. Our article on the complete finishing of oil paintings contains more detailed information about the process.
Applying the Paint
In theory, there are two techniques for painting with oil paints: alla prima (from the Italian alla prima—in one go) and multi-layer painting.
Alla prima refers to painting wet-on-wet. This technique involves mixing the paints both on the palette and on the canvas itself, and applying them before the underlying colors have dried. Thus, the painting consists of a single layer and is completed while the paint is still wet. Cobra water-soluble oil paint can be applied undiluted, mixed with water, or Cobra painting medium.
Multi-layered paintings, on the other hand, are built up gradually, with each subsequent layer applied only after it is certain that the one below is dry enough so as not to soften or dissolve. To achieve this, the principle of “oil over linseed oil” is followed —each subsequent layer contains more oil than the previous one.
Oily on dry
It is recommended that the first coat be thin and diluted with water.
As it dries, this layer of paint remains porous, absorbing and retaining the oil from the next, oilier layer, which creates good adhesion. It is precisely because the oil penetrates so deeply that we must ensure that each subsequent layer is oilier. Otherwise, the risk of various defects later on increases.
The resulting adhesion— or the strong bond between the layers— absorbs and neutralizes the tension between the layers of paint. This tension is caused by the constant contraction and expansion of the painting due to the elasticity of the stretched canvas and changes in temperature and humidity.
The higher the oil content in the flower layer, the more elastic it will be once it hardens. If we violate the “oil over linseed oil” principle, the harder, less elastic upper layers would crack due to the movement of the lower layers. That is why the paint must be allowed to dry sufficiently before adding another coat—paint that is not yet dry is often too elastic for the next layer, which leads to cracks.
Each artist decides for themselves how many layers their painting will consist of. After applying the first “base” layer, diluted with water, and allowing it to dry, there are two ways to proceed:
- Each subsequent layer should contain less water and, consequently, be oilier than the previous one. In the final stage of the painting, pure paint may be used.
- The colors should be built up using a painting medium consisting of oil, resin, and water. The oil makes the paint greasy, the water balances the oil content, and the resin increases the durability of the layer.
If the painting consists of more than two layers, the medium can initially be diluted proportionally with water, gradually transitioning to pure medium, thereby adhering once again to the basic principle.
Painting with very diluted paint
The first coat of paint can be thinned with plenty of water. However, this is not recommended for the final coats, since it is the oil that protects the pigments. For painting with very fluid paints, we recommend adding at least 20% Cobra working medium to the water.
Glazing / Velatura
Whether we’re painting wet-on-wet or using multiple layers, we can finish our painting with a “glaze” —a transparent layer of color that doesn’t alter the painting but changes its hue and effect. In this way, the artist can also adjust certain nuances they are not satisfied with without having to repaint them. Glazing with one or more layers can also give the colors a stained-glass effect (also called glazing) and deepen them.
Glazing is done using a sufficient amount of liquid transparency medium, which eliminates brush marks. This also allows for color gradients within the glaze itself. The “wet-on-dry” rule still applies here—the glaze must be more elastic than the layer onto which it is applied. For this purpose, you can use Cobra’s transparency medium.
It’s hard to tell how many layers it will take to achieve a satisfactory result. That’s why it’s a good idea to pay attention to the oil content of the paint. We do not recommend using pure oil as a medium, as it seals the paint and prevents the next layer from adhering to it. Furthermore, using too much oil carries the risk of the paint wrinkling as it dries.
Varnishing
Water-mixable paints can be varnished with both standard oil varnish and specialized Cobra varnishes , available in three varieties – gloss , matte and semi-matte/satin . The difference between them is in the solvent: traditional varnishes consist of resin dissolved in pure white spirit or one mixed with turpentine, while Cobra varnishes are made only with white spirit. For matte and satin varnishes, a matting agent is added.
Varnishes protect the colors and give them their shine. Good varnishes can be removed without damaging the paint, even after many years.
In terms of drying, the water-soluble version of oil paints is no different from the traditional one— the paints dry through the chemical process of oxidation, which is influenced by the amount of light and oxygen. Once they have fully hardened, the oxidation process transitions into aging, which manifests as fine cracks. The drying time prior to this varies depending on the layer—it can take anywhere from a few months to several years. The right time to apply the top coat is immediately after the initial stage of paint curing (polymerization). This way, we even out the brightness of the colors, protect them from the elements, and slow down the further aging of the painting.
During the varnishing process , the components involved—the painting and the varnish—must be at room temperature. For example, if the painting is brought from a cold room into a warm one, condensation may form on its surface; the moisture from this condensation could become trapped under the varnish and eventually cause it to turn white. This same moisture would prevent the varnish from spreading evenly and adhering properly to the paint, causing small droplets to form.
Drops may also form if the paint layer is too tightly sealed due to its high content of painting medium or oil. To prevent this, wipe the painting with a cloth dampened with a small amount of white spirit; once it has evaporated, the varnish can be applied.
Cobra in combination with other types of paint
Made entirely from oil, water-soluble Cobra paints can be mixed with traditional oil paints and the media compatible with them. However, the more regular oil paint we add to them, the less we can use water as a thinner afterward.
Many beginning artists have the misconception that water-mixable oil paints can be freely mixed with other painting media, such as acrylics. However, the difference in the resistance of the two types of paint would lead to premature cracking and even peeling of the layers.
If we really want to use acrylic as well, it can be applied as a quick-drying colored base coat. To do this, it must be diluted with water just enough to remain porous enough for the oil paint to adhere to it. If applied thickly, the acrylic layer would be too isolating and quite flexible. As a result, the oil paint on top of it would crack as it hardens.
Translated from Royal Talens’ Artists’ Materials Manual (2020) by Martina Petrova
