Oil paints are the most complex to use from a technical standpoint when it comes to their durability.
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.
The traditional method for preparing the base involves applying rabbit glue or gelatin (animal glue). These prevent the oil from being absorbed into the canvas and further stretch the fabric after it dries. A partially absorbent primer is then applied; its porous structure absorbs the oil, which penetrates through it and bonds to the glue underneath. There are many recipes for making this type of primer, such as calcium carbonate (chalk) mixed with animal glue or oil paint.
The modern alternative to this more complicated-to-prepare primer is a group of products known collectively as “gesso.” The word “gesso” derives from the Greek γύψος (gypsos)—meaning “gypsum”— and its use is permitted by all manufacturers. The Talens gesso that we offer is made with pure acrylic resin and is of superior quality. Canvases and our mounted panels are pre-primed with gesso and ready for painting.
With its unique formula, the primer performs the functions of the various types of insulating coatings mentioned above. However, the layer must be sufficiently thick, so it is best to apply two coats; the first of which can be thinned with water to make it easier to spread. The second coat remains undiluted or is thinned with a little water. If the substrate is highly absorbent, it can first be treated with Amsterdam’s acrylic primer, whichis a pure, colorless acrylate. Afterward, the two layers of gesso are applied in two crosswise directions.
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 the wet-on-wet painting technique. 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. The paint is applied in its pure form or mixed with a medium/solvent.
Multi-layered paintings, on the other hand, are built up gradually, with each subsequent layer applied only after it is certain that the layer beneath is dry enough so as not to soften or dissolve. To achieve this, the “oil-on-linseed oil” principle 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 thinned with turpentine or white spirit.
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’s why you have to wait for the paint to dry sufficiently before applying another coat—paint that hasn’t dried 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, thinned with a medium, and allowing it to dry, there are two ways to proceed:
- Each subsequent layer should contain less thinner and, accordingly, 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 a solvent. The oil makes the paint oily; the solvent prevents it from becoming too oily; and the resin increases the durability of the layer.
If the painting consists of more than two layers, the medium can initially be thinned with turpentine or white spirit and then gradually switched to pure medium, thereby adhering once again to the basic principle.
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’re 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 erases brush strokes. 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.
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
Varnishes and lacquers for oil paints usually consist of resin and a solvent. They protect the colors and determine their sheen. High-quality varnishes can be removed with a solvent, even after many years—for example, to restore a painting—without damaging the paint.
Touch-up Polish
During the drying process, dry spots may appear on the surface of the painting. This happens when these areas have absorbed too much oil—a defect that, left unchecked, would continue into the subsequent layers. Dry spots can be corrected with retouching varnish, which is applied after the paint has dried to the touch; it restores the painting’s luster, restores color harmony, and prevents excessive oil absorption. This type of varnish remains porous, so that when more paint is applied, it can adhere to it. This application also distinguishes it as an intermediate varnish.
Elbow retouching can also serve as temporary protection for paintings that are not completely dry. It evens out the sheen and protects them from dirt while allowing the oxygen needed for the paint to continue hardening to pass through. Once the paint is completely dry, a final coat of varnish can be applied.
It is important to always apply touch-up nail polish in a thin layer. Using too much of it prevents subsequent layers from adhering and can dissolve the oil in the base, causing it to rise to the surface. This would leave the painting sticky for many months or even years, making it prone to soiling. In other words, on paints of normal viscosity, retouching varnish should be applied only after at least 2–3 months.
Topcoat
Oil-based paint dries through the chemical processes of oxidation —absorbing oxygen from the air—and polymerization. Once it has dried thoroughly (which takes about a year for a medium-thick coat of paint), it is recommended to apply a final coat of varnish. The drying time prior to this varies depending on the layer—it can range from a few months to several years. After curing, the paint enters an aging phase, which we see as cracking. Topcoats slow down oxygen absorption and the aging process, determine the gloss of the colors, and provide lasting protection against weathering and pollutants.
During the varnishing process, every element involved must be at room temperature —the painting, the varnish, the brush, and the containers used. 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 turn white. That 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, you can apply the varnish.
Glossy topcoats consist mainly of resin and solvent.
Matte, on the other hand, also includes matting agents. It is good to mix before application and then apply with movements in the same direction for an even matting. Only one coat of liquid varnish is applied to avoid the formation of visible stains or brush marks. If the matte varnish is in the form of a spray, we can afford to repeat the layer.
The matting agent in Talens varnish is made from a combination of waxes that solidify at low temperatures. To melt them and homogenize the varnish, you need to warm the bottle, for example, in a water bath.
Translated from Royal Talens’ Artists’ Materials Manual (2020) by Martina Petrova
