The watercolor technique flat wash is a process for painting large, solid-color backgrounds or underpainting for glazing and for smaller areas and objects in a composition using the wet-on-wet technique.
A sufficient amount of watercolor paint and water needs to be mixed ahead of time so that the color value is consistent throughout the flat wash process. If you have to stop to mix more watercolor with water, the paper will become dry, and your wash mixture will most likely not have the same color value as your initial wash.
For covering large areas, use a one-inch flat brush or an oval “wash brush” (also called a “mop brush”). To paint smaller areas with a wet-on-wet wash, use a round brush size 10 or larger.
Controlling the brush and the painting speed is important. The wetness of the paper needs to be consistent until the desired area is covered with the flat wash. The tip of the brush should lightly touch the paper and move across the paper in a smooth, horizontal stroke.
When the flat wash is complete, leave the paper tilted at a slight angle on a board or easel until it has dried completely. Then proceed with painting the rest of your watercolor composition.
Why the Flat Wash Is a Foundational Watercolor Technique
Although flat washes are often used for skies, backgrounds, and underpainting, this technique is one of the most important skills to master in watercolor painting. Flat washes teach essential control over water, pigment load, timing, and brush movement. These same skills are required for more advanced techniques such as glazing, graded washes, and expressive wet-on-wet effects.
Practicing flat washes consistently helps develop confidence and precision, making them an excellent foundational exercise for both beginners and experienced painters.
Choosing the Right Paper for a Successful Flat Wash
Paper choice plays a major role in how evenly a flat wash behaves. Professional, artist-grade watercolor paper—especially 100% cotton—allows the wash to stay workable longer, giving you more time to complete the area without streaks or hard edges.
Cold press paper offers enough texture to hold pigment evenly, while hot press paper produces smoother, sharper washes but dries more quickly. Lightweight papers tend to buckle, causing paint to pool unevenly and making consistent washes more difficult to achieve.
Using Gravity to Control a Flat Wash
The slight tilt of the paper during and after a flat wash is a subtle but crucial detail. Angling the paper (at least 10–15 degrees) allows gravity to guide the flow of pigment downward in a controlled manner. This creates a small bead of paint that helps prevent streaks and uneven drying.
Painting on a completely flat surface increases the risk of blooms and patchy areas, especially when working on larger sections.
Flat Wash vs. Graded Wash: Understanding the Difference
A flat wash maintains a single, consistent color value across the entire painted area. In contrast, a graded wash transitions gradually from dark to light or from one color intensity to another.
Learning to control a flat wash first makes graded washes significantly easier, as both techniques rely on the same principles of timing, water control, and brush movement.
Color Mixing Tips for Flat Wash Consistency
Before applying a flat wash, always mix more paint than you think you will need. Granulating pigments may naturally settle unevenly, creating texture even in a flat wash, while staining pigments tend to produce smoother, more uniform results.
Testing your wash on scrap paper helps confirm both color value and flow before committing to your painting surface.
Common Flat Wash Problems and How to Avoid Them
Even experienced painters encounter challenges with flat washes. Common issues include:
- Streaks: Caused by inconsistent moisture or uneven brush pressure
- Blooms (cauliflowers): Occur when wetter paint is introduced into a partially dried wash
- Uneven color: Often the result of insufficient paint mixture or stopping mid-wash
Understanding why these problems occur makes them easier to prevent with practice.
Using Flat Washes as Underpainting for Glazing
Flat washes are frequently used as an underpainting for glazing techniques. A smooth, even base layer establishes color harmony, light direction, and mood early in the painting process. Since glazes are transparent, any unevenness in the flat wash will become more noticeable as additional layers are applied.
A well-executed flat wash provides a strong foundation for luminous, layered watercolor paintings.
Practicing Flat Washes as a Skill-Building Exercise
Practicing flat washes regularly—such as painting full sheets in a single color—helps develop an intuitive understanding of water-to-paint ratios and drying time. Try repeating the exercise with different pigments and paper types to observe how each material behaves.
Flat washes make excellent daily warm-up exercises and are one of the most effective ways to improve overall watercolor control.
Recommended Watercolor Paper for Flat Wash Painting
Use 140 lb cold press archival 100% cotton rag watercolor paper. It is advisable to stretch the watercolor paper first to prevent it from buckling if you plan to cover the paper with a wet-on-wet wash. To avoid stretching the paper, I recommend using a watercolor paper block.
Cotton paper withstands repeated wetting and drying better than cellulose paper, making it ideal for wet-on-wet techniques.