Impasto is paint laid on a canvas or panel in quantities that make it stand out from the surface and is usually thick enough that brush or palette knife strokes are visible. The first known use of the word was in 1784, from the Italian impasto, the noun of the verb impastare, “to put in paste.” (Harper, 2013)
The heavy viscosity and slow drying time of oil paint make it a suitable medium for the impasto painting technique. Watercolor and tempera paint are not satisfactory for this technique because they lack these properties and do not form continuous films surrounding pigment particles.
Thick passages of paint can serve several functions in paintings. First, the relief of impastos can intensify highlights by increasing the light-reflecting properties of the paint. This effect extends the tonal range of the painting by making highlights appear more brilliant. Second, skillfully and minutely worked impastos can depict wrinkled skin or the texture of intricately crafted surfaces of jewelry and fabrics, such as in the works of Rembrandt, Frans Hals, and Diego Velázquez. The nineteenth-century painter Vincent van Gogh used impastos to build up and define the forms in his paintings with thick daubs of paint so that the viewer could see the strength and speed by which the artist applied the paint, giving them added expressiveness. Fourth, impastos can emphasize the physical qualities of the paint itself, as seen in the works of such twentieth-century painters as Jackson Pollock and Willem de Kooning.
The combination of chiaroscuro and impasto in Rembrandt’s paintings shows an affinity with the method of Titian, who was the first to use thickly applied and dragged impasto. This marked the innovation of replacing the painterly means of direct representation with a method of suggestion and illusion. (Liedtke, 1995)
Rembrandt used impastos to accentuate highlights by the increased illumination of surfaces facing the light source and the exaggeration of shadows on surfaces facing away from the light source. It appears that this was the sole intention of the impasto in the illuminated parts of the face in the Self Portrait of 1659 at the National Gallery in Washington. The brushstrokes are scarcely related to the form of the face. (De Wetering, 1997)
It is unclear exactly how Rembrandt created the textures encountered in the lights of his portraits, most notably the skin textures of male subjects. It may be reproduced by building up thick layers of opaque paint and then dragging a soft brush over the surface while it is still wet. In most cases, after executing highlights in thick layers, Rembrandt would eventually wholly or partially cover these with thin paint as glazes.
As Rembrandt developed this glazing technique over impastos, he employed a fast drying white consisting of lead white, chalk, leaded crystal glass, and smalt. The increasingly heavier impastos in paintings of his later period, modified by thin glazes of color, created illusory special effects, an extreme example of which is the man’s golden sleeve in The Jewish Bride in the Rijksmuseum in Amsterdam.
Impastos can be obtained by using a high proportion of pigment combined with unmodified oil, which, over some time, results in dry, hard paint. The relatively stiff paint needed for impastos can also be obtained using a heat-bodied thickened with metal salts, such as lead, which gives a soft appearance and a relatively yielding paint. Analysis suggests that Rembrandt used heat-bodied and unmodified oils with a larger proportion of pigments in his impastos. (White, 1994)
Heat polymerization has several effects on the oil. Drying properties are improved and further enhanced by adding metal salts during the heat-bodying process. The refractive index of the oil is increased, thereby increasing the saturation of the pigment color. The high molecular weight of polymerized oils increases the oil’s flow out and leveling, giving the paint film a glossier appearance. The pigment is less liable to sink in the oil film, which changes less in volume than an unmodified oil film, reducing the amount of wrinkling that may occur. White paints are less susceptible to yellowing because, as the polyunsaturated fatty acids initially present in the paint film are destroyed by the formation of carbon-carbon single bonds, there is less possibility for the formation of colored organic compounds, the presence of which gives the yellow appearance to the film.
The character of impastos achieved by freshly applied paint consisting of a larger proportion of pigment to oil, especially with such pigments as lead white and lead-tin yellow, is different from that provided by heat-bodied oil. The highly varying and often commented appearance of Rembrandt’s brushwork in his thickly-applied passages could have been obtained by the juxtaposition of paint consisting of heat-bodied oil and unmodified oil containing a high proportion of pigment.
Much of the thickest impastos in Rembrandt’s paintings are formed of lead white, sometimes with lead-tin yellow. Where lead white is used in thick passages, it does not produce excessive cracking as the paint film dries and ages because, prevalent with all lead-containing pigments, lead white enhances the drying of oil paint, forming a particularly tough and flexible film. (Bomford, 2006)
Rembrandt used chalk as a pigment in its own right and an extender in impastos, where bulk without the density is required in the paint. When mixed in oil, chalk is virtually transparent, making it suitable as a modifying agent for glazing paints that also contain translucent colored pigments. The effect of adding chalk to oil paint is to add body and translucency to glazes without inducing a significant color change.
The complexity and variety of techniques in Rembrandt’s paintings set him apart from his contemporaries. The thickly-applied paint often consists of distinct hues and values forming broken-color passages. Separately applied colors remain clean and distinct and can be seen from an average viewing distance, as in the painting of the Man with a Magnifying Glass. This attention to detail in brushstrokes recalls Roger de Pile’s remark that Titan and Rembrandt knew that some colors should not be overmixed but should be touched as little as possible with the brush. De Piles praised Rembrandt for his flesh colors which are “not less true, less fresh, nor less exquisite than Titian’s,” and remarked that his way of using color is unique. (de Piles, 1715)
(Harper, 2013) Douglas Harper, Online Etymology Dictionary, retrieved June 7, 2013. http://www.etymonline.com/index.php?term=impasto
(Liedtke, 1995) Walter Liedtke, Carolyn Logan, Nadine M. Orenstein, Stephanie S. Dickey, “Rubens and Rembrandt: A Comparison of Their Techniques,” Rembrandt/not Rembrandt in the Metropolitan Museum of Art, New York: Metropolitan Museum of Art, 1995, p. 78, 79.
(De Wetering, 1997) Ernst Van De Wetering, Rembrandt: The Painter at Work, Amsterdam University Press, 1997, p. 220.
(White, 1994) Raymond White and Jo Kirby, “Rembrandt and his Circle: Seventeenth-Century Dutch Paint Media Re-examined,” National Gallery Technical Bulletin Volume 15, 1994.
(Bomford, 2006) David Bomford, Art in the Making: Rembrandt, Yale University Press, 2006, p. 36
(de Piles, 1715) Roger de Piles, Abregé de la vie des peintres, 2nd ed., Paris, 1715.