Wavelength
Less than 10 nm
Wavelength
~320-400 nm
Wavelength
~400-700 nm
Wavelength
~900-1700 nm

Visible Light

Cross- Section

Ultraviolet

Infrared

X-ray

Infrared Reflectography

infrared
visible light

Infrared reflectography (IRR) provides details about paint layers that are beneath the surface. Gainsborough used a dark paint to cover the abandoned portrait before painting The Blue Boy. Move the slider above to see what it looks like under infrared light.

Infrared imaging reveals Gainsborough’s preparatory lines, including one along the side of the boy’s body; it also shows his use of foliage to cover the dog.

Infrared reflectography (IRR) uses wavelengths beyond the red end of the light spectrum to look through the upper paint layers. What can be seen depends on the thickness of the paint, the type of paint used, and the IRR wavelength. For instance, IRR displays how Gainsborough covered over an earlier portrait with dark paint. Only the face and the outlines of the shoulders were painted, confirming that he abandoned the portrait at an early stage.

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Visible Light

Some condition issues are readily visible under normal light. For example, this detail from The Blue Boy’s far left edge illustrates that the overpaint, or non-original colors added during past conservation, has become discolored.

This detail shows where a thinly painted area has worn away, barely concealing the abandoned portrait of a man wearing a thick white neckcloth.

This detail from the back of the frame displays where Charles Holmes, then director of London's National Gallery, wrote his goodbye before the painting left for the United States: “Au revoir, CH.”

Raking light, or light angled across the painting, highlights texture: how the paint was applied and where it is cracked or lifting from the surface.

Visible light reveals details about the artist’s techniques and the materials that were used to create the painting. By carefully studying the surface, a conservator may discover such condition issues as abraded or cracked paint or discolored overpaint that no longer matches the surrounding original paint.

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Cross-Section Analysis

elemental
analysis
visible light
cross-section

On the left is a cross-section of a minuscule sample from the painting’s top edge, showing the colors and materials that were used in each layer. Move the slider above to see a color-coded map of the individual elements.

Cross-section analysis involves embedding a tiny sample in resin and viewing all of the layers under a microscope. This type of analysis shows that The Blue Boy’s bottom layer, a double ground, contains lead white and chalk, with some yellow ocher and a few black particles mixed in to create an off-white preparatory layer. The abandoned portrait’s flesh tones were created with lead white and vermilion, which was then covered by a layer of gray.

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Ultraviolet Light

ultraviolet
visible light

Ultraviolet (UV) light reveals details about the materials that are not visible to the human eye. Move the slider above to view The Blue Boy under UV light.

UV illumination shows overpaint from previous restorations; the overpaint absorbs UV light, but the varnish fluoresces.

Ultraviolet light helps conservators distinguish certain surface materials, such as varnishes or overpaint, because they interact differently with this type of light. A particular varnish, for instance, may fluoresce, or reflect back a characteristic color. Overpaint, on the other hand, may not fluoresce, revealing where prior conservation work has occurred.

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X-radiography

x-ray
visible light

X-rays penetrate the layers of a painting, showing how it was made or changed by the artist. Move the slider above to view an X-ray of The Blue Boy.

X-rays reveal the details of a man’s face, a repaired tear in the lower left, and a dog that Gainsborough initially painted, then decided against.

X-rays provide a glimpse of a portrait that Gainsborough began but then abandoned before deciding to reuse the canvas.

X-rays pass through all of the layers of a painting, showing ones that are invisible from the surface. This can provide clues about how a painting was made, the ways in which the artist changed the composition, and evidence of earlier damage. For instance, X-rays of The Blue Boy capture the complexity of Gainsborough’s layered brushstrokes, especially in the costume. They also reveal the structure and condition of the underlying wooden support.

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Credits

Text and photos by Christina O'Connell
User interface design by Catherine Bell

SEM-EDS analysis and imaging of cross-sections courtesy of Dr. Gregory D. Smith, Indianapolis Museum of Art at Newfields

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