Non-laser light divestment in conservation and preservation John F. Asmus * Institute for Pure and Applied Physical Sciences, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0360, USA Abstract Over the past 10 years, laser technologies have found acceptance for surface divestment both in industry and in art conservation. The initial endeavors in exploring and assessing the utility of this art conservation tool are recounted for investigations involving ruby, glass, ion, YAG, carbon dioxide, dye, and excimer lasers with particular emphasis on the limitations that were encountered with each (in terms of speed, cost, wavelength, spectral width, and reliability). In response to these issues, a research effort is described that was instituted to assess non-laser (viz., incoherent) light sources (e.g., flashlamps, sparklamps, arclamps, and pinchlamps) for radiation cleaning. Initial demonstration projects with these sources included Parisian textile theater seats, leather-bound books, architectural stencil designs, courthouse ironwork, and Ming Dynasty marble statues. With non-laser light generators, substrate thermal alteration and debris redeposition often present problems. These may be minimized or avoided through the incorporation of a gas jet, static liquid, liquid jet, or dry-ice blast. © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Laser conservation; Cleaning; Divestment; Flashlamp; Pinchlamp; Surface modification 1. Introduction Soon after the discovery of laser divestment for art conservation [1], it became clear that laser surface treat- ments were too expensive for widespread utilization. Whereas laser investment, operating, and maintenance ex- penses have dropped and reliability has improved, costs can still be high in comparison to conventional cleaning. Numerous early radiation-divestment projects had to be accomplished with non-laser sources through economic necessity. With the advances in laser performance, many applications can now be cost-effectively accomplished with modern lasers. However, many classes of large-scale surface-divestment processing still require lower-cost pho- tons than can be produced with commercially available lasers. Prior to the invention of high-performance commercial lasers, the standard high-intensity light generator for com- mercial and domestic applications had been the xenon flashlamp (viz., the electronic photoflash). It had been used for decades in high-speed photography, beacons, and lithog- raphy. Some flashlamps were capable of producing tens of megawatts of optical power (e.g., for dye-laser pumping). However, flashlamp technology is incapable of generating the directivity and spectral purity of a laser. On the other hand, flashlamp systems are simpler, less costly, and more efficient than lasers of comparable power and energy. This is especially the case at the short wavelength end of the spectrum from the green through the ultraviolet. As spectral purity and directivity are unimportant in many laser-cleaning applications, the xenon flashlamp may afford an adequate low-cost alternative to the laser. Some examples are described in this paper. For challenging applications, advanced lamps such as the pinchlamp or the vortex lamp are described that offer performance advan- tages. 2. Surface divestment with flashlamp radiation Flashlamp cleaning was first attempted with encrusted marble and limestone objects based on the favorable results attained with lasers in these circumstances. Satisfactory results were only occasionally achieved [2]. Sometimes, a residue remained. Frequently, the skin of the stone experi- enced vitrification and a change in color (usually to brown). SEM analyses of the vitrified skin usually revealed the presence of microscopic shrinkage cracks that did not bode well for the conservation state of the surface material. Shortening the flashlamp pulse length (from milliseconds to * Corresponding author. E-mail address: jfasmus@ucsd.edu (J.F. Asmus). Journal of Cultural Heritage 4 (2003) 56s–58s www.elsevier.com/locate/culher © 2003 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 1 2 9 6 - 2 0 7 4 ( 0 2 ) 0 1 2 2 8 - 1