The Shaw Memorial was sculpted by Augustus Saint-Gaudens (1848-1907), one of the foremost American artists of the nineteenth and early twentieth centuries. The memorial commemorates the death of Colonel Robert Gould Shaw and the men in his command who died in an assault on Fort Wagner (near Charleston, South Carolina) on July 18, 1863.

Colonel Shaw commanded the 54th Massachusetts, the first black infantry regiment raised in the North during the Civil War. Their story was recently depicted in the movie Glory.

Cast in bronze, the immense sculpture measures 4.45 m high by 5.36 m wide by 0.28 m deep (14.6 ft by 17.6 ft by 34 in. deep). It was installed on an imposing pedestal on Boston Common, where it still sits today and faces the Massachusetts State House.

But Saint-Gaudens did not sculpt in bronze - he created a masterpiece in plaster that was subsequently cast in bronze. A perfectionist, he made changes in the plaster even after the bronze was cast.

The final version of the plaster was exhibited in 1901 at the Pan-American Exposition in Buffalo, New York. Since 1959 it has been located outdoors at the Saint-Gaudens National Historic site in Cornish, New Hampshire.

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The sculpture was in serious danger of damage brought about by years of exposure to the elements.

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Greater than life size, the plaster weighs 2,800 kg (6,150 lb), consisting of 21 interlocking sections supported by an armature made up of iron pipes, bars, wire, and other materials.

The sculpture was originally gold-leafed to provide a bronze "look," and re-coating has occurred several times.

However, the sculpture was in serious danger of damage brought about by years of exposure to the elements. The plaster had cracked, and some of the support materials were believed to have rusted or otherwise decomposed.

Accordingly, an effort was undertaken to conserve the plaster memorial at the Smithsonian Institute, to cast it in bronze, and to return the bronze to Cornish in 1997 for permanent exhibition. The plaster sculpture will be on loan to the National Gallery in Washington, DC.

 

The Problem
Since 1959 the sculpture has stood in Cornish on a concrete base, inside a three-sided roofed structure with a concrete rear wall.

The framework was thought to be attached to the rear (concrete block) wall by twisted metal wires held by metal clips set into the mortar between the blocks.

Visibility, however, was extremely limited. The number of such clips was unknown, as were their exact locations. Nothing could be seen of the manner in which the sculpture was attached to the base.

To make things worse, neither the internal structure nor the means of attaching the plaster to its surroundings had been documented.

 

The Solution
Forcibly moving portions of the sculpture from the base or the backwall might have provided a great deal of much needed insight into how the sculpture was held in place, but this was quickly ruled out as being too likely to damage the plaster. What was needed was a way to get that insight without running the slightest risk of damage. This meant subjecting the sculpture to a comprehensive X-ray examination.

This was done in May 1996 by Conam Inspection, Inc., of Auburn, Massachusetts, using a radiation source and Structurix X-ray film from Agfa Division of Bayer Corporation.

Before arriving at the site, the film was loaded into typical industrial "flex" cassettes. Within each cassette, the unexposed film is sandwiched between lead screens that serve to intensify the exposure of images taken during the X-ray process, as well as to absorb scatter radiation that might otherwise degrade those images. Externally, the cassettes are sheathed in a bluish polyvinyl wrap that protects the film from light and dirt.

The inspection technique used is illustrated in Figure 1. An image on X-ray film is produced when photons of radiation energy cause a darkening of silver crystals in the film. The more intense the energy, the darker the image. The best example of this is the radiation energy that reaches the film without having to first go through the structure being examined, in this case the sculpture.

Figure 1 - Basic concept of inspection using X-ray technique.

Radiation energy traveling through an object, however, is attenuated by that object. The denser the object, the greater the attenuation, the lower the degree of silver crystal darkening, and the lighter (whiter) the resultant X-ray image on film. To compensate for this attenuation with denser objects, radiographers sometimes use faster film.

In general, however, slower films show finer details than fast film. To avoid losing the ability to detect fine details, one does not want to use any film faster than necessary. In most X-ray exams, this is not a problem because the density of the test object is usually known.

The density of Saint-Gaudens’ plaster is known, but since the location of the framing members was unknown, the density distribution behind the plaster was also unknown.

To make certain that the entire armature and attachment systems were located and identified as clearly as possible, different speeds of Agfa film were used.

As shown in Figures 2-6, an extensive series of radiographs was taken. As an example, the radiograph in Figure 7 is indeed eerie, but it clearly shows the position of the support system within the upper portion of the horse-mounted figure, the one representing Colonel Shaw.

Figure 2 - Shaw Memorial plaster sculpture as it has been displayed since 1959 at Cornish, New Hampshire.

 

Figure 3 - Technicians prepare to X-ray area where sculpture is attached to base. Note "flex" film cassettes.

Figure 4 - Close-up of film cassettes at base of sculpture.

Figure 5 - Cassette being moved into position for X-ray examination of Colonel Shaw figure (on horse).

 

Figure 6 - Cassette located for examination of upper portion of Colonel Shaw figure.

 

Figure 7 - X-ray image taken from cassette position as shown in Figure 6.

 

The X-ray examination of the Shaw Memorial was quite successful. It provided extensive knowledge of the sculpture’s framework, as well as of the nature and location of the base and rear wall attachments.

More importantly, it provided the knowledge that allowed this priceless work of art to be dismantled so it could be preserved for posterity.

 

* Joule Associates, 8 Carter Ln., Wesley Hills, NY 10952; (914) 354-5413; fax (914) 362-0208; e-mail rmh@pipeline.com

Copyright © 1997 by the American Society for Nondestructive Testing, Inc. All rights reserved.

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