Oil paint dries and hardens through a chemical process called oxidation and crosslinking, which involves reactions with oxygen from the air.
The Drying Process Explained
Unlike water-based paints that dry primarily through evaporation, oil paints undergo a more complex transformation. This process can be broken down into the following stages:
- Oxygen Absorption (Oxidation): Initially, the oils in the paint (like linseed oil) absorb oxygen from the air. This absorbed oxygen reacts with the unsaturated fatty acids in the oil.
- Polymerization (Crosslinking): The oxygen absorption leads to the formation of free radicals, which then cause the oil molecules to link together, forming a complex, interconnected network. This process, called polymerization or crosslinking, creates a solid, durable film.
- Volatile Organic Compound (VOC) Emission: During the drying process, some low-molecular-weight oxygenated compounds are produced. These compounds evaporate, contributing to the characteristic smell of drying oil paint and a slight mass loss.
Key Aspects of Oil Paint Drying
- Drying Oils: The type of oil used in the paint significantly impacts the drying time. Linseed oil is a common drying oil.
- Pigments: Pigments can influence the drying rate; some pigments act as catalysts, speeding up the process, while others can inhibit it.
- Temperature and Humidity: Warmer temperatures generally accelerate drying, while high humidity can slow it down.
- Layer Thickness: Thicker layers of paint take longer to dry because oxygen needs to penetrate throughout the layer.
In essence, oil paint doesn't simply "dry" by evaporation like watercolor. Instead, it solidifies and hardens through a chemical reaction with oxygen, leading to a robust and lasting paint film.
