Oil Paint Cracking: Causes, Pigments, and How to Prevent Damage in Your Artwork

Oil painting cracking is a phenomenon that often perplexes artists and conservators alike. Why do some paintings develop cracks over time while others remain relatively intact? Recent research by Fuster-López et al., titled “Selective Cracks: Mapping Damage from Pigment-Medium Interaction in Three Neoplasticist Oil Paintings,” provides valuable insights into these questions. This study explores the causes of selective cracking in modern oil paintings, focusing on how specific pigments, mediums, and environmental factors contribute to the degradation of artworks. The findings offer crucial lessons for artists seeking to create durable works and conservators tasked with preserving cultural heritage.

What Causes Cracks in Oil Paintings?

Cracks in oil paintings result from complex interactions between materials, techniques, and environmental conditions. The study identifies two primary contributors to cracking: the intrinsic properties of the materials and external environmental influences.

The researchers discovered that cracking often originates from the chemical and physical properties of the pigments and binders used in paints. For example, paints with poor drying properties or unstable pigment-medium interactions are more prone to cracking. These cracks are not uniformly distributed; instead, they tend to form selectively in areas where certain pigments are present. This suggests that the cause lies in the inherent characteristics of the materials rather than external conditions alone.

The Role of Pigments in Oil Paint Cracking

The cracking of oil paintings is significantly influenced by the pigments artists choose, as their intrinsic properties directly affect the stability and behavior of the paint film. The study by Fuster-López et al. sheds light on specific pigments that exhibit a propensity for cracking, offering detailed insights into their interactions with binders and other materials. Understanding these mechanisms is essential for artists who aim to create works with long-term stability.

Revealing Hidden Cracks in Georges Vantongerloo's Composition dans le cône avec couleur orange: This figure demonstrates the power of ultraviolet reflectography (UVR) in revealing otherwise invisible details in Georges Vantongerloo's Composition dans le cône avec couleur orange (1929). The left panel shows the UVR image, highlighting subtle cracks in the paint layer that are imperceptible to the naked eye. These cracks, located primarily in the lighter geometric areas, underscore the importance of advanced imaging techniques for identifying material vulnerabilities. The right panel zooms into a detailed section, showcasing the intricate patterns of the cracks, which may be linked to the inherent properties of the pigments used and their interaction with the binder. This analysis highlights the critical role of UVR in conservation, allowing for precise documentation and targeted interventions to preserve the structural and aesthetic integrity of modernist artworks. (Images from the authors.)

Infrared Transillumination Reveals Structural Details in Georges Vantongerloo's Composition dans le cône avec couleur orange: The images illustrate how infrared transillumination (IRT) exposes underlying structural details in Georges Vantongerloo's Composition dans le cône avec couleur orange (1929). The left panel presents the full IRT image, effectively highlighting the morphology and distribution of cracks within the painting's layers, providing a clearer view of the structural instabilities obscured in visible light imaging. The right panel offers a close-up detail, revealing the directionality and extent of these cracks. The IRT technique also captures variations in paint thickness and impasto, where darker areas denote denser, thicker paint applications. This non-invasive approach underscores its value in diagnosing material degradation and informing conservation strategies for preserving modernist compositions.

White Pigments: Contrasts in Stability

White pigments are among the most commonly used in painting, yet their chemical and mechanical properties vary significantly, leading to differing crack patterns:

Zinc White: Zinc oxide-based pigments often form compact paint films but are prone to developing short micro-cracks. This behavior stems from the pigment’s tendency to form metal soaps, which can disrupt the paint’s structural integrity. These soaps can manifest as small protrusions on the surface, weakening the cohesion of the paint layer.

Titanium White: Frequently used by modern artists, titanium white exhibits high UV absorbance but does not luminesce under ultraviolet light. The non-luminescent property of titanium white indicates a high level of light absorption and scattering within the visible spectrum, contributing to its excellent opacity in paint. These characteristics allow titanium white to effectively mask underlying layers, providing strong coverage even when applied in thin films. This property is particularly advantageous for artists seeking a bright, reflective white with minimal translucency. The study by Fuster-López et al. suggests that the qualities contributing to titanium white’s opacity may also make it more susceptible to brittleness. Non-luminescent pigments exhibit reduced flexibility because they lack the inherent reactiveness with drying oils, hindering the binder’s ability to form a cohesive, elastic film, particularly over time or under environmental stress.

Pigments composed of elements such as iron, cobalt, or lead are known as reactive pigments, meaning they actively catalyze the oxidation and polymerization processes of drying oils, resulting in faster and more uniform drying. These pigments chemically interact with the oil medium to form cohesive paint films, which reduces the risk of uneven drying. In contrast, non-reactive pigments like titanium white lack this chemical interaction with the binder. Titanium white does not participate in the oxidative drying process, which can leave the binder to dry unevenly around the pigment particles. This can lead to areas of stress concentration within the paint film, increasing its brittleness and the likelihood of cracking over time. The study by Fuster-López et al. highlights that these stresses are particularly evident in thick applications of titanium white.​ Artists should consider this characteristic when working with titanium white, balancing its strong opacity with other pigments that promote drying.

Lead White: Despite its historical prevalence, lead white demonstrates a different behavior. When exposed to UV light, it often forms a luminescent layer, making cracks more visible to conservation scientists. Its more flexible film formation properties render it less prone to micro-cracks than zinc white but still vulnerable to broader, network-like cracks in areas with significant environmental stress.

Red Pigments: Cadmium Red and Its Challenges

Cadmium-based pigments, widely used throughout the 20th century, are known for their vibrant hues and durability. However, they also present challenges:

Cadmium Red: The study identified cadmium red as a frequent component in the red areas of the analyzed paintings. This pigment exhibits selective cracking due to its interaction with binders, especially when applied in thick layers or combined with drying oils that have limited flexibility. Cadmium red often shows a strong luminescent response under UV light, which indicates its potential for instability in certain formulations. The cracking in cadmium red areas is typically influenced by its concentration in the paint film and the drying characteristics of the medium.

Blue Pigments: Distinct Behaviors of Cobalt and Ultramarine

The study provides a nuanced understanding of blue pigments, highlighting their contrasting behaviors in terms of cracking:

Cobalt Blue: A widely used pigment in modern oil painting, cobalt blue is a reactive pigment that accelerates the binder's drying process. While this property is beneficial for faster drying, it also contributes to irregular, medium-sized cracks. These cracks result from the pigment’s influence on the mechanical properties of the paint film, which becomes brittle over time.

Ultramarine Blue: Unlike cobalt blue, ultramarine blue develops fine, random cracks. This difference stems from its distinct spectral behavior and weaker drying properties. Ultramarine blue does not interact with binders as aggressively as cobalt blue, resulting in a comparatively more stable film. Ultramarine is a hydrophilic pigment, which means it has a natural affinity for water that can influence its stability under varying environmental conditions, particularly in high-humidity environments. While this property was not a primary focus of the study, it is well-documented in the literature as a potential vulnerability in ultramarine-based paints. Hydrophilic pigments can attract and retain moisture, potentially leading to swelling or microstructural changes in the paint film over time. This could result in degrading the binder-pigment interaction and an eventual weakening of the paint layer's integrity.

Yellow Pigments: Complexity in Identification

Yellow pigments showed significant variability in their cracking patterns due to differences in composition:

Cobalt Yellow: Identified in some of the yellow areas, cobalt yellow demonstrated a brownish-greenish appearance under UV light and a blackened surface under UV false-color imaging. These visual properties suggest a complex interaction with binders, potentially leading to micro-cracks or fissures over time. Cobalt yellow does not luminesce strongly, unlike cadmium-based yellows, which may reduce its visibility in certain imaging techniques.

Organic Yellows: The study also identified the potential use of organic yellow pigments mixed with other colors. These pigments are less stable over time and may contribute to fine micro-cracks, especially in areas exposed to significant environmental fluctuations. Organic yellows include the azo family of yellow pigments

The study underscores the importance of selecting pigments with known chemical and mechanical properties. Artists should consider the aesthetic qualities of pigments and their long-term stability. Mixing incompatible pigments or binders can exacerbate cracking while selecting flexible binders and avoiding thick paint applications can help mitigate these issues. Additionally, artists should be mindful of how their choice of white pigments, particularly, affects their paintings’ structural integrity over time.

Oil Paint Cracking and Environmental Factors: Myths and Realities

While environmental factors such as humidity, temperature fluctuations, and light exposure are often blamed for cracking, the study demonstrates that intrinsic material properties play a more significant role. However, this does not mean environmental factors are irrelevant. Environmental stressors can accelerate degradation, especially when combined with unstable materials. For instance, fluctuations in humidity can exacerbate the formation of cracks in already compromised paint films.

The research encourages artists to use materials with stable properties and to store and display their works in controlled environments to minimize potential damage.

Imaging Techniques: A Window into Material Behavior

The authors used advanced imaging techniques, including ultraviolet-induced luminescence (UVL), infrared photography (IR), and ultraviolet false color (UVFC), to study the cracks in three early 20th-century Neoplasticist paintings. These methods allowed researchers to map cracks, identify pigments, and understand how materials interacted over time. For artists, this underscores the importance of understanding how their materials will age and respond to environmental stress.

Lessons for Artists: Creating and Preserving Durable Paintings

Material Selection: Choose pigments and binders with stable chemical and mechanical properties. Avoid using pigments known for their instability unless combined with stabilizing mediums.
Test paint formulations to understand how they will interact over time.

Techniques: Apply paint in thin layers to ensure even drying. Uneven paint thickness can lead to stress points, increasing the likelihood of cracking. Avoid mixing incompatible pigments and mediums, leading to chemical reactions that weaken the paint film.

Environmental Precautions: Display and store paintings in environments with stable humidity and temperature levels. Fluctuations can exacerbate pre-existing weaknesses.
Use UV-filtering glass or coatings to minimize light-induced degradation.

Documentation: Document the pigments, oils, and other materials used in your painting to assist with any future restoration efforts and help you troubleshoot issues as they appear in your artwork.

The findings of this study are a call to action for artists to pay closer attention to the materials and methods they use. Cracking is not merely a result of time and environmental exposure; the materials' properties deeply influence it. By understanding these factors, artists can create paintings that stand the test of time.

This research also reminds us that conservation begins in the studio. Every decision, from pigment selection to painting technique, has a long-term impact on the durability of the artwork. By integrating the lessons from this study into their practice, artists can ensure that their works endure as vibrant testaments to their creativity.

Bibliography

Fuster-López, Laura, Miguel Ángel Herrero-Cortell, Francesca C. Izzo, Ana María García-Castillo, Marcello Picollo, Costanza Cucci, and Maite Martínez-López. 2023. “Selective Cracks: Mapping Damage from Pigment-Medium Interaction in Three Neoplasticist Oil Paintings.” In Working Towards a Sustainable Past: ICOM-CC 20th Triennial Conference Preprints, Valencia, 18–22 September 2023, edited by Janet Bridgland. Paris: International Council of Museums.
Access the article here.

Insights from Luminescence: Implications for Oil Paint Crack Formation

The study by Fuster-López et al. highlights luminescence as a diagnostic tool for understanding pigment behavior and its relationship to crack formation in oil paintings. Luminescence, the ability of a material to emit light when exposed to specific wavelengths, not only serves as a diagnostic tool for identifying pigments but also has implications for the mechanical stability of paint films. It reveals critical information about the stability of certain pigments and their interactions with binders.

Luminescent pigments, such as cadmium reds, cobalt blues, and zinc whites, show distinct behaviors under ultraviolet (UV) light. These behaviors often correlate with vulnerabilities in the paint film:

Localized Weakness: Areas with luminescent pigments are prone to stress due to UV-induced chemical changes or heat. Over time, this stress can weaken binder-pigment interactions, leading to selective cracking.

Pigment Concentration: Higher luminescence often reflects higher pigment concentration. As the pigment-binder balance shifts, these areas can become brittle, increasing the likelihood of cracks in zones with intense luminescence.

Metal Soap Formation: In pigments like zinc white, luminescence is linked to the formation of metal soaps, which disrupt the paint’s surface and trigger cracks.

The findings on luminescence illustrate how material choices impact the longevity of paintings. Understanding its implications equips artists to understand how scientists evaluate paintings and the causes that lead to cracking.