
Hard lines (also referred to as tidelines) are often visible along the edges of a watercolor stroke, and result from the deposit of pigment particles as the paint dries; an excellent example of this can be seen in the photomicrograph detail above of Paul Cézanne's The Balcony. The field of view is 3/4" in diameter.
Watercolor
The luminosity of an expertly rendered watercolor relies on the interplay of individual and overlapping color washes and the white of the paper. The transparent washes allow light to pass through and reflect back from the paper beneath, so that overlapping strokes combine optically to produce new colors. If sufficient drying time is not allowed before applying the overlying strokes of color, the moist colors will run together, an effect Charles Demuth, among others, controlled and used to his advantage. Watercolor has been used since ancient times, even predating the use of paper. It appeared very early in Egyptian papyrus paintings, and later on parchment in Medieval illuminated manuscripts. Watercolors consist of finely ground pigments or dyes suspended in water by means of a plant gum, generally gum arabic. As the paint dries, the coloring agents stain the support or are stuck to its surface by the gum.
Shown above are a paint box containing pans of watercolor and, to the left, materials used to manufacture watercolor paint - powdered pigment at top, and granular gum arabic below.

Sample swatches on a page from A Descriptive Handbook of Modern Water-colour Pigments
Examples from the Collection

The Balcony, c. 1900
Paul Cézanne, French
Watercolor and graphite on wove paper (recto and verso)
Sheet: 22 1/4 × 15 7/8 inches (56.5 × 40.3 cm)
A. E. Gallatin Collection, 1943
1943-75-1
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Paul Cézanne, French
Watercolor and graphite on wove paper (recto and verso)
Sheet: 22 1/4 × 15 7/8 inches (56.5 × 40.3 cm)
A. E. Gallatin Collection, 1943
1943-75-1
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Glance of a Landscape, 1926
Paul Klee, Swiss
Watercolor, sprayed through stencils and brushed, on paper, mounted on board inscribed by the artist
Sheet: 11 7/8 × 18 1/8 inches (30.2 × 46 cm)
The Louise and Walter Arensberg Collection, 1950
1950-134-120
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Paul Klee, Swiss
Watercolor, sprayed through stencils and brushed, on paper, mounted on board inscribed by the artist
Sheet: 11 7/8 × 18 1/8 inches (30.2 × 46 cm)
The Louise and Walter Arensberg Collection, 1950
1950-134-120
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In Vaudeville (Dancer with Chorus), 1918
Charles Demuth, American
Watercolor and graphite pencil on laid paper
Sheet: 12 11/16 × 8 1/16 inches (32.2 × 20.5 cm)
A. E. Gallatin Collection, 1952
1952-61-18
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Charles Demuth, American
Watercolor and graphite pencil on laid paper
Sheet: 12 11/16 × 8 1/16 inches (32.2 × 20.5 cm)
A. E. Gallatin Collection, 1952
1952-61-18
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