Oil painters have long known that the choice of drying oil is vital to the success and endurance of their work (Mayer, 1991, p. 28). The three most commonly used oils—linseed, walnut, and poppy seed—each influence drying time, color stability, flexibility, and surface qualities in distinct ways (Schultz, 2020). Selecting the appropriate oil is crucial for ensuring the longevity of a painting. Different oils behave uniquely over time due to their chemical composition and drying properties. Understanding these differences allows artists to make informed decisions about layering, blending, and preservation. This article explores the key differences among these oils, their impact on painting techniques, and best practices for their application to achieve both aesthetic and structural integrity.
Seeds and nuts—sources of traditional drying oils.
Understanding Drying Time in Drying Oils
Drying time affects how an artist structures their painting sessions and layers. Linseed oil dries the fastest, taking just a few days for thin layers to become touch-dry, while walnut and poppy seed oils can remain wet for weeks (Winsor & Newton, 2021). This difference can be beneficial when extended blending is desired. However, if the slow-drying layers are buried beneath quicker-drying layers, cracking may occur as the underlying paint continues to cure and contract (Mayer, 1991, p. 33).
The drying process results from oxidation, where the oil reacts with oxygen to form a polymerized film. Tumosa and Mecklenburg (2012) discuss how the oxidation rate varies among different oils, with linseed oil undergoing the most rapid cross-linking due to its high linolenic acid content. Walnut and poppy oils, which contain fewer polyunsaturated fatty acids, dry more slowly and are more susceptible to long-term changes in flexibility and adhesion.
The Importance of Color Stability in Drying Oils
Linseed oil has a strong track record of forming robust paint films, but it can yellow over time, especially if stored away from light (Schultz, 2020). Walnut oil yellows less, which makes it a popular choice for vibrant colors. Poppy seed oil remains the clearest, often selected for delicate tints and whites where color purity matters (Molesky, 2017). The tendency of linseed oil to yellow results from the formation of chromophores during oxidation, a process that can be mitigated by exposure to light (Tumosa & Mecklenburg, 2012).
Color stability is especially critical in the upper layers of a painting, particularly in whites or light blues, since any yellowing or discoloration can be more noticeable there (Molesky, 2017). While no oil is entirely resistant to discoloration, artists can strategically use less-yellowing oils in upper layers to maintain a painting’s original vibrancy. Understanding these properties enables painters to make informed decisions when layering colors, ensuring both longevity and visual integrity.
Considering Flexibility in Drying Oils
Flexibility prevents cracking as a painting ages. Linseed oil has a high linolenic acid content, which helps it form durable, elastic films (Mayer, 1991, p. 34). Walnut oil, though slightly less robust, remains stable and flexible enough to endure if not overused in thick layers. By contrast, poppy seed oil produces a more brittle film and demands cautious application. It is generally reserved for upper layers or final touches to reduce stress on the paint surface (Molesky, 2017).
The polymerization process that occurs as drying oils cure affects long-term flexibility. With its high concentration of linolenic acid, linseed oil undergoes rapid polymerization, resulting in a highly cross-linked and elastic film. Walnut oil, containing more linoleic acid and less linolenic acid, polymerizes at a slower rate, leading to a moderately flexible film that remains softer over time. Poppy seed oil, which has the lowest degree of unsaturation among these three, forms the least cross-linked structure, making it more brittle and prone to cracking as it cures. These differences in polymerization influence how each oil responds to environmental factors such as humidity and temperature fluctuations, affecting the overall durability of a painting.
Texture and Handling in Drying Oils
Each oil influences the consistency of the paint. Linseed oil can create a smooth, flowing texture, walnut oil provides a silky, easily blended feel, and poppy oil encourages an ultra-creamy consistency that lengthens working time (Schultz, 2020). Many artists combine oils or use them selectively based on the specific brushwork and surface effects they want to achieve. For instance, Leonardo da Vinci experimented with walnut oil, favoring its slow drying properties and smooth blending for delicate transitions in skin tones. The Flemish masters, including Jan van Eyck, strategically layered linseed and walnut oils to balance strength and color vibrancy, ensuring both durability and visual depth in their paintings.
Volume Loss, Solvent Disruption, and Paint Stability in Drying Oils
One crucial consideration in oil painting is the long-term volume loss associated with different drying oils. Research has shown that as drying oils cure, they undergo oxidation and polymerization, reducing volume over time (Izzo et al., 2014). This shrinkage affects the structural integrity of the paint film, potentially causing cracking, wrinkling, or surface distortion.
Long-term weight loss in various drying oils over 1,200 days. Cold-pressed linseed oil shows significantly less weight loss compared to walnut and poppy seed oils, making it more resistant to solvent diffusion over time. Some oils exhibit a net loss in weight, indicating severe polymer degradation that can persist for years, weakening the paint film (Tumosa & Mecklenburg, 2012).
Linseed oil, known for its strong cross-linking properties, exhibits the least volume loss, making it a reliable choice for foundational layers. Volume loss is particularly problematic for underlayers because as the paint film contracts, it can lead to tension between layers, causing cracks and delamination over time. Ensuring a stable base with minimal shrinkage is essential for the longevity of a painting, preventing structural failures that could compromise the artwork’s integrity. Additionally, Tumosa and Mecklenburg (2012) found that linseed oil films maintain their structure better over time due to lower loss of volatile compounds, reducing the risk of voids or microchannels forming within the paint. Walnut oil experiences moderate volume reduction, while poppy seed oil suffers the highest volume loss due to its lower oxidative polymerization capacity (Izzo et al., 2014). Research by Tumosa and Mecklenburg (2012) further confirms that poppy seed and walnut oils experience greater weight loss over time, which can contribute to polymer degradation, leading to increased solvent sensitivity and embrittlement. This difference reinforces the importance of selecting linseed oil for underpainting, where stability is critical, and using poppy seed oil only in uppermost layers where minimal structural impact occurs. Moreover, solvent interactions should be carefully managed, as extensive weight loss in poppy and walnut oils can make them more susceptible to damage from aggressive cleaning methods, further compromising paint film integrity (Tumosa & Mecklenburg, 2012).
Best Practices for Longevity
Proper technique and thoughtful oil selection ensure the lasting preservation of an artwork. An underlayer made with linseed oil, applied in a lean manner, can provide a stable foundation for subsequent layers that include walnut or poppy oils (Winsor & Newton, 2021). Avoid using poppy seed oil in underpaintings because it dries so slowly and forms a brittle underfilm, which can lead to cracks in subsequent layers (Mayer, 1991, p. 36). Attention to the fat-over-lean approach ensures that the upper layers remain sufficiently flexible to prevent cracking. Additionally, understanding solvent interactions is critical for conservation efforts, as excessive exposure to strong solvents can remove essential binding components and weaken the paint film’s structure over time (Tumosa & Mecklenburg, 2012).
Choosing the Right Drying Oil
The choice of drying oil plays a fundamental role in oil painting, influencing everything from drying time and color stability to long-term structural integrity. Linseed oil remains the most durable and reliable for foundational layers, while walnut and poppy oils offer advantages in blending and color preservation. By carefully selecting and layering these oils, artists can optimize drying time, maintain color stability, and ensure structural integrity.
Bibliography
Books and Academic Sources
Mayer, Ralph. The Artist’s Handbook of Materials and Techniques. New York: Viking, 1991.
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Summary: Mayer’s book examines painting materials and techniques, including the chemical properties and practical applications of drying oils. It is a widely regarded resource for both historical and contemporary artistic practices.
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Abstract: The text offers a comprehensive discussion of materials used in oil painting, including linseed, walnut, and poppy seed oils, their drying properties, and their impact on color stability and film durability.
Tumosa, Charles S., and Mecklenburg, Marion F. “Oil Paints – The Chemistry of Drying Oils and the Potential for Solvent Disruption.” Smithsonian Contributions to Museum Conservation, 2012.
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Summary: This study investigates the oxidation and polymerization of drying oils, weight loss trends over time, and the vulnerability of oil paint films to solvents. The authors analyze the role of different oils in preserving structural integrity.
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Abstract: The research provides insights into how oil paints age, the effects of oxidation, and how solvent exposure can degrade the polymer matrix in oil paintings.
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Link: [Not available]
Izzo, Fiorenzo, Van Loon, Annelies, and Noble, Petria. “Modern Oil Paints – Formulations, Organic Additives and Degradation: Some Case Studies.” Heritage Science, 2014.
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Summary: This study examines the formulation of modern oil paints, focusing on organic additives and the degradation mechanisms of oil paint films. The research highlights volume loss due to oxidation and polymerization.
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Abstract: The paper discusses the role of different drying oils in modern paints and how volume loss and chemical changes influence the structural integrity of paintings.
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Link: https://heritagesciencejournal.springeropen.com/articles/10.1186/s40494-014-0014-8
Industry and Technical Reports
Winsor & Newton. “What Are Drying and Semi-Drying Oils?” Winsor & Newton Website, 2021.
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Summary: This technical article explains the differences between drying and semi-drying oils, particularly their use in oil painting. It details drying times, yellowing tendencies, and recommendations for optimal use.
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Abstract: A practical guide for artists on how different oils, such as linseed, walnut, and poppy seed oils, affect painting techniques and long-term preservation.
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Link: https://www.winsornewton.com/na/articles/oil-colour/what-are-drying-and-semi-drying-oils/
Artist and Conservation Articles
Schultz, Dan. “Color Stability: Walnut vs. Linseed Oil.” Dan Schultz Fine Art, 2020.
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Summary: Schultz’s article explores the color retention properties of walnut and linseed oils, comparing their effects on whites and lighter hues over time.
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Abstract: The author provides photographic comparisons demonstrating the yellowing tendencies of linseed oil and how walnut oil offers improved color stability for artists working with lighter palettes.
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Link: https://www.danschultzfineart.com/color-stability-walnut-vs-linseed
Molesky, David. “Walnut Oil as a Medium – History & Chemistry.” Artist’s Road, 2017.
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Summary: This article examines the historical use of walnut oil as a painting medium, particularly by Renaissance masters such as Leonardo da Vinci.
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Abstract: The research details the chemical properties of walnut oil and its advantages in producing smooth, flexible paint layers while resisting yellowing.
