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Examination with Infrared Radiation

So far in this discussion all of the techniques used to examine the print and decipher the restorations are relatively straightforward and low tech.

A final and innovative technique used to image the repairs uses thermal infrared radiation (thermography).

For years conservators have used near infrared reflectography to examine works of art in order to see underlying materials and to distinguish between materials that would otherwise look the same. IR reflectography has enabled conservators to look at works of art and learn more about artist's materials and techniques, physical make-up and condition. Infrared reflectography has had its greatest application in painting conservation in the study of underdrawing or underpainting. (See CMA web entry for conservation exhibition The Mass of Saint Gregory: Examining a Painting Using Infrared Reflectography.)

For the examination of works of art on paper, particularly Western prints and drawings, IR reflectography has had a more limited application simply because there are typically no layers to see through and thorough examination with various natural light sources, i.e., raking and transmitted, usually reveals the essential information about condition, materials, and artists' technique.

Cleveland's Battle of the Nudes and Examination with Infrared Radiation

Here are the front and back views of the Cleveland print captured with near IR reflectography. Some of the repairs are indicated in these images and our ability to detect them is aided by a prior knowledge of their characteristics.

Image of 84. Pollaiuolo, <I>Battle of the Nudes</I>, CMA first-state impression, overall view front captured using near infrared reflectography.
84. Pollaiuolo, Battle of the Nudes, CMA first-state impression, overall view front captured using near infrared reflectography.
Image of 85. Pollaiuolo, <I>Battle of the Nudes</I>, CMA first-state impression, overall view of verso captured using near infrared reflectography.
85. Pollaiuolo, Battle of the Nudes, CMA first-state impression, overall view of verso captured using near infrared reflectography.
Now look at the front and back views of the print captured with thermal infrared radiation. The amount of information that can be gleaned from a seemingly plain flat piece of paper using thermal IR imaging is quite extraordinary; from the back of the print in particular the repairs are clearly visible, and visible in a manner not previously encountered or anticipated.

Image of 86. Pollaiuolo, <I>Battle of the Nudes</I>, CMA first-state impression, overall view of front captured using thermal infrared reflectography.
86. Pollaiuolo, Battle of the Nudes, CMA first-state impression, overall view of front captured using thermal infrared imaging (thermography).
Image of 87. Pollaiuolo, <I>Battle of the Nudes</I>, CMA first-state impression, overall view of verso captured using thermal infrared reflectography.
87. Pollaiuolo, Battle of the Nudes, CMA first-state impression, overall view of verso captured using thermal infrared imaging (thermography).
Both views of the print captured with thermography are composites, pieced together from 20 individual pictures using Adobe PhotoShop. The composite for the front image was extremely difficult to obtain as the recorded raw data was slightly uneven in scale and tonality and fitting all of the pieces together required extensive manipulation in the software program. For the front view, a fairly small amount of information was lost during the process of reassembling the pieces. This was not a setback, however, as the vast majority of information initially captured came from the back of the print; this image suffered virtually no loss during reassembly.

All of the major restoration sites (as well as several minor ones not discussed) are clearly imaged because every material has unique chemical and physical properties and will absorb, transmit and reflect radiation, in this case ambient heat, in a distinct and characteristic way. The thermal infrared camera equipped with a specialized lens is so sensitive that even very similar papers can be distinguished in the captured images.

It is important to point out that not all of the details captured and imaged with thermography are understood at this time and much more experimentation looking at various papers (prints and drawings), with and without repairs, is necessary to become more proficient at interpreting the thermograms.

Thermal IR imaging is a new examination technique at the Cleveland Museum of Art and its full potential with regard to many different materials and types of art has yet to be explored. Its usefulness in finding and helping to identify repairs that previously went undetected or were not fully understood is clearly demonstrated in the case of this print.

Conclusion

Implicit in this presentation is that despite all the admiration they evoke, the historic repair techniques presented here are (typically) not practiced today by paper conservators. The techniques for all their merits are now regarded as too invasive: they necessitate too great a loss of original undamaged material and, undetectable or not, too great an alteration to the art. Contemporary paper conservators are not averse, when possible, to making beautiful and invisible repairs provided they are properly documented. For fine art in particular such attention to aesthetic concerns is entirely appropriate. However, current thinking is that the physical and historical integrity of the art cannot be subordinated to the opportunity or one's ability to make highly cosmetic and invisible repairs. Consider Schweidler's comment regarding a successful tear repair where he explains that "if all the printed lines join well then no retouching is necessary as no damage was done to the print during scraping." While it would be difficult to argue that the actual image is not more important than a blank surface on the opposite side, current teaching and practice considers the integrity of the art to include the back; in Schweidler's day (early to mid-twentieth century) it did not.

To understand the shift in attitude and approach to treatment that is being alluded to here in a very specific manner, it is useful to consider some of the developments in the discipline of art conservation that emerge in the twentieth century but have only taken hold in the last fifty years or so. Perhaps the most evident change is one of terminology: the term "restoration" itself has been replaced with "conservation" and "restorer" with "conservator". Conservation encompasses restoration but places heavy emphasis on preservation - that is, taking preventive measures to avoid damage in the first place. For example, sound preservation relies on implementing good storage and handling practices, limiting light exposure on light sensitive materials, and maintaining a clean environment and stable climatic conditions with respect to temperature and relative humidity.

Another trend is an increasing awareness of and reliance on scientific analysis and technology. This development is very aptly illustrated here with the use of thermal IR radiation to image the repairs in this print. The ability to uncover information that will help us interpret works of art as well as inform our decisions as to how to best treat and preserve them is immensely enhanced by scientific and technological resources.

The later part of the twentieth century has seen an expanded concern for the physical, aesthetic, conceptual, and historical integrity of works of art and material culture. This combined with a heightened recognition of the fact that interpretation of artifacts and technical know-how will change over time is seen in the move towards minimal and reversible treatment procedures. Conservators embrace the adages "less is more" and "better is the enemy of good." This approach to treatment leaves room for reinterpretation, and provides a certain peace of mind in that if later we change our minds, no "harm" will have been done.

In the nineteenth and early twentieth centuries, a good amount of mystery surrounded the restorer's craft; trade secrets were a means to succeed in a growing and competitive art (and print!) market. Now conservation requires a free and open sharing of information and encourages collaboration. Research findings and treatment experiences are exchanged through publications and conferences. The need to educate and raise the performance of the profession overall is seen in the development and refinement of documentation procedures and efforts at standardization - this includes establishing accredited graduate conservation training programs and professional organizations, which provide members with a conservation code of ethics and standards of practice.[Bibliography: See Kosek; Brueckle; and Cohn]

Despite marked shifts in attitude and our ever evolving ethos concerning the discipline of art conservation it is no surprise that conservators are generally eager to study Schweidlers and other historic restoration manuals carefully. There is always the possibility of coming across techniques and tips for augmenting ones own treatment repertoire but more importantly, through these resources, conservators are better equipped to understand and care for works of art that have old repairs -- repairs that when skillfully executed are not only admired but now regarded as integral to the art.



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