Décoloration d'une peinture à l'huile

Oil paints are indeed quite delicate and demand a significant amount of knowledge and skill to master. Success in oil painting involves not only the ability to create the desired image but also an understanding of the techniques and principles that prevent damaging a beautiful artwork.

We previously discussed the fat-over-lean technique and its complexities. Now, I would like to highlight another crucial issue: fading. Fading is a prevalent condition that affects many oil paintings, and it can be quite disheartening, as it is irreversible and can compromise hours of hard work. I have personally experienced the disappointment of having several paintings damaged by fading due to my oversight of some fundamental guidelines. So, what causes fading? Let’s take a closer look at the drying process to identify some of the key factors that contribute to this issue.

The drying process of an oil painting layer is quite intricate, beginning at the top surface where oil molecules “capture” oxygen from the air. As the top layer cures, it forms a barrier that restricts oxygen from penetrating further. Subsequently, the film becomes thinner and more porous, allowing oxygen to move deeper and cure the entire layer. Natural, soft daylight acts as a catalyst for this reaction, along with temperature, which should ideally be maintained between 15 and 25°C for linseed oil and between 25 and 35°C for walnut oil. Any disruption to these optimal conditions can pose a risk for fading. Below is a list of the most common causes of fading.

A bad quality of canvas or grout

As previously mentioned, oil paint can dry unevenly, particularly in areas exposed to oxygen. While we often assume that the top layer is the most affected, this is not always the case. Canvas, being a fabric, consists of threads that create micro-holes, allowing oxygen to penetrate. To mitigate this issue, it is essential to properly glue and grout the canvas. Thicker fabrics are preferable, as they have fewer holes, and the quality of the gluing and grouting process significantly impacts the canvas’s performance.

Always inspect the canvas under light; if you can see light passing through the threads, it indicates that the canvas requires treatment before use. The grout itself plays a crucial role as well. Basic grouts typically contain acrylic emulsion, calcium bicarbonate, titanium white, and various additives. It is important to note that calcium bicarbonate is highly porous, which can drain oil from the painting layer, leading to a deficiency of oil in the top layer and resulting in fading over time.

Poor Drying Conditions

Insufficient light and low temperatures can significantly slow down the drying process of oil paintings, extending it by 5 to 10 times. This unnatural delay prevents the top layer from forming properly, leading to a faded appearance in the artwork. Additionally, if the environment where the painting is drying has high humidity, the drying time will be further prolonged, causing the surface to lose its gloss and appear matte and dull.

Incorrect painting process

To enhance the flexibility and vibrancy of your painting layers, I recommend using mediums that include copal, turpentine, or other gums. These mediums not only help your artwork last longer but also contribute to a brighter appearance. While they do add a gloss finish, you can manage this by adjusting the ratio in your painting medium, incorporating linseed oil or turpentine oil as needed.

When applying layers, ensure that each previous layer is completely dry. A semidry layer can draw oil from the newly applied layer, potentially leading to fading. It’s generally better to apply two thin layers rather than one thick one. However, if you’re using impasto techniques, ensure that all subsequent layers are either the same thickness or thicker than the previous ones.

For glazing, opt for mediums that contain sufficient oil and gums, as mineral spirits do not provide adequate oil content for the layer. This deficiency can result in cracking and peeling after the paint has fully dried, which can take several months. Please note that varnishing will not prevent or remedy these issues.