What is the most widely used drying oil in painting?

Linseed oil is the most widely used drying oil in painting due to its excellent drying properties and versatility. When exposed to air, linseed oil undergoes a process called oxidation, which allows it to harden and form a strong, durable film. This characteristic makes it particularly valued in the production of oil paints and varnishes. It not only enhances the color and gloss of the paint but also improves the flow and workability, facilitating smoother application.

Other oils listed, such as castor oil, vegetable oil, and sunflower oil, do not offer the same film-forming properties or drying benefits that linseed oil provides. Castor oil is primarily used in cosmetic and medicinal applications rather than in traditional painting. Vegetable oil generally refers to a broad category of oils and lacks the specific drying characteristics needed for painting. Sunflower oil, while also an edible oil, does not harden effectively when exposed to air compared to linseed oil, making it less suitable for use in artistic applications.

Thus, linseed oil stands out as the preferred choice in the painting industry, allowing artists and contractors to achieve lasting finishes in their work.