How External Environments Affect the Physical Behavior of Different Painting Materials

Through long-term practice and visual observation, it becomes clear that a painting material's behavior is not determined solely by its formula. Air exposure, temperature, humidity, time, and the properties of the surface it is applied to all continuously participate in shaping its physical state.

Below is a record of how different painting materials physically evolve under the influence of various environmental factors, drawn directly from hands-on observation:

1. Alcohol and Volatile Liquids

Alcohol and liquids that rely on alcohol as their main vehicle are the most sensitive to open air.

• Sealed vs. Open States: In a sealed container, pure alcohol remains essentially stable. If the liquid contains trace moisture, water droplets will gradually condense on the inside walls of the container over time. Once exposed to open air, the liquid evaporates rapidly, steadily losing volume until it completely vanishes. Pure alcohol leaves no residue upon evaporation, whereas alcohol inks leave their pigment on the surface once the liquid medium disappears. This evaporation process is irreversible.
• Effect of Heat: Applying heat (such as using a heat gun) increases the rate of evaporation and shortens the drying time, but it does not change the basic physical transition of the liquid turning into a gas.
• Long-Term Behavior: After colored liquids evaporate completely, the pigment remaining on the surface is still affected by the environment. If the underlying surface lacks sufficient grip (adhesion), the dried marks may flake or peel over time. Prolonged exposure to air and sunlight can also cause the remaining colors to fade or shift.

2. Powdered Pigments

Dry pigments before being mixed with binders show significant variation in environmental sensitivity depending on the specific color origin.

• Outdoor Conditions: When exposed to long-term outdoor conditions, high-and-low temperature cycles, day-to-night temperature swings, and ambient moisture will accelerate deterioration in sensitive pigments, causing them to absorb dampness, clump, change color, or lose their free-flowing texture. However, highly stable pigments under the exact same outdoor conditions will retain their original state for years.
• Indoor Storage: Indoor environments are relatively stable, but if stored in open containers over time, pigments with high moisture affinity will still absorb moisture from the air and gradually form clumps. Their scent may also shift slightly through exposure to air components.

3. Liquid Pigment Pastes (Pourable Paints)

Once pigment powder is mixed with liquid binders into a fluid paste, its sensitivity to temperature and humidity becomes much more drastic.

• Temperature Effects: In high temperatures or outdoor environments, fluid paste systems tend to ferment faster and build up gas bubbles inside. When stored completely sealed, this internal pressure build-up can cause the liquid to leak out from the container, accompanied by a stronger smell. In cooler indoor temperatures, fermentation and gas build-up slow down significantly, but pigment particles and binder liquids are more prone to visible settling and layer separation.
• Bottling and Drying: As the paste turns from liquid to solid during drying, moisture evaporation causes the scent to weaken gradually. Higher temperatures speed up evaporation. However, for certain pigments, if the surface skin dries too quickly while internal moisture has not yet escaped, the interior can form hollow pockets, surface shrinkage, or cracking as it dries out.

4. Solid Watercolors

Once completely dried into solid watercolor cakes, their sensitivity to everyday indoor conditions drops significantly. However, environmental changes can still re-engage their behavior.

• Re-activation by Humidity: In high-humidity air, the surface of dry watercolors will re-absorb moisture from the air, becoming tacky, soft, or causing separate paint cakes to stick together.
• Dry-to-Wet Color Shift: When activated with water and painted onto a surface, the color looks deeper and more saturated while wet. As the water evaporates completely and dries, the color typically lightens, with some shades taking on a slightly muted or grayish appearance. The absorption and reflective characteristics of the paper itself also directly impact how the final dried color appears.
• Long-Term Structure: Prolonged exposure to strong light causes certain pigments to fade. Because watercolor layers are applied extremely thin, the internal tension created during drying has already been fully released, meaning it will not crack, shatter, or flake off like heavy, thick paints do.

5. Acrylic Paints

Environmental effects on acrylic paints are concentrated during the phase when wet paint transforms into a solid film.

• Curing Process: Sealed inside a container, acrylics maintain a stable paste consistency. Once exposed to open air, moisture evaporation drives the paint to gradually solidify into a tough, plastic-like paint film. This process is irreversible; once fully dry, the film cannot be re-dissolved or restored to its liquid state by adding water.
• Long-Term Structure: Color shifting after curing is minimal. However, during long-term storage, if the paint layer is applied very thick or subjected to bending forces, localized cracking, splitting, or peeling away from the underlying surface can occur.

6. Oil Pastels

Oil pastels are made from wax, oil mediums, and pigments. They exist naturally as solids at room temperature and do not rely on the evaporation of water or solvents to dry out.

• Long-Term Stability: Whether exposed to open air or kept sealed in a box, their color, shape, and texture remain virtually unchanged for many years, with only their natural scent fading over time. Even on artwork stored for years, the surface can still be reworked, scraped, or blended using palette knives or tools—there is no fixed "cure" point.
• Temperature and Firmness: Their physical state is distinctly regulated by temperature. Under high temperatures, oily components tend to seep to the surface, increasing gloss, softening the texture, and making colors easier to blend. In cold temperatures, the material hardens and becomes stiffer. This shift in firmness is completely reversible as temperatures fluctuate.

Comparative Physical Responses of Materials to Environmental Factors

The external environment is not just an isolated background setting; it works together with the material's physical state (powder, liquid, solid), time, and the underlying surface to determine the final result. The different responses shown by these materials are simply natural physical behaviors occurring continuously across their lifecycle.