Lasers and the Fine Art of Art Conservation

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  • Daniel Dawes

    R esearch on analyzing and cleaning art with lasers has abounded in the UnitedStates since the early 1990s at universities such as Harvard, Duke and theUniversity of California at San Diego. Still, only one major U.S. museumthe Los Angeles County Museum of Artregularly uses the technology. John Miller, a laserscientist at Oak Ridge National Laboratory for 23 years and currently a grant review man-ager for the Department of Energy in Gaithersburg, Md., is among those who feel lasersoffer great promise for the art conservation world.

    I believe that safe, effective techniques have been demonstrated and the time is ripe forlaser ablation cleaning to be incorporated into the conservators arsenal of tools, Millersaid. Lasers are now available in a growing variety of sizes, wavelength ranges and powers.Also, importantly, many are now turnkey lasers that can be operated safely by those whoare not Ph.D.-level [scientists].

    Although there has been sporadic research into laser cleaning since the birth of the laser in the 1960s, the large spurt in research came when the Europeans began to provide[more] funding for cultural heritage type projects, Miller said. The accumulated researchinto laser-materials interaction in the physics and chemistry communities also led to alarge number of labs and scientists with the right experience to think about applicationslike art conservation.

    16 Optics & Photonics News September 2004

    Most museums in the United States are not entrusting their pricelesspaintings and statues to laser cleaning, but as lasers become cheaper,safer and more precise, art conservators may find them hard to ignore

    as replacements for more traditional cleansing techniques.

    1047-6938/04/09/0016/4-$0015.00 Optical Society of America

    Lasers and the Fine Art of Art Conservation

  • September 2004 Optics & Photonics News 17

    Daguerreotypes, which were madefrom iodine-coated plates, were the first commercially available

    photographs. They were popularbetween 1840 and 1860. Scientist John

    Miller cleaned the daguerreotype onthe facing page using a Nd:YAG laser.

    Tell us what you think: http://www.osa-opn.org/survey.cfm

  • Still, Miller understands why art conservators are wary of lasers. He hasworked mostly with daguerreotypes, thefirst commercially made photographs,which were developed in the mid-1800s.If lasers arent used carefully, they can doirreparable damage to an object.

    But so can conventional cleaning ifdone by inexperienced people, he said.In earlier eras, daguerreotypes werecleaned quite effectively with chemicals.But after the passage of time the processturned out to have inflicted invisibledamage that was only evident years later.I believe that the techniques of laser-ablation cleaning must be perfected anddemonstrated on similar media first.Then a partnership between laser scien-tists and conservation professionals mustguide the application.

    The techniques Laser researchers at American universitiesare experimenting with several differenttechniques for analyzing and cleaning art.

    The methods include laser-inducedfluorescence, where a low-intensity lasergives a fluorescence emission identifiableby its spectral features to analyze both

    organic and inorganic materials, such as paints and varnishes.

    Laser-induced breakdown spec-troscopy (LIBS) is a technique in whichthe spectrum of ionized material is ana-lyzed and the encrustation on metal andstone is ablated. Only one-tenth of ananogram of the material is burned offper pulse, and LIBS can give more selec-tive, unambiguous results than laser-induced fluorescence.

    Raman spectroscopy is a nondestruc-tive laser-based technique in which a laserbeam is reflected off a sample and thewavelengths that are different from that ofthe laser are measured. In this technique,the pigments under study are identifiedthrough matching of the wavelengths oftheir molecular chemical bonds.

    While at Oak Ridge, Miller used LIBSto analyze daguerreotypes. A daguerreo-type is an image exposed onto a mirror-polished copper plate in a box camera.The plate was light sensitized with iodine,placed in the camera, exposed to an imagefor one to two minutes, developed withmercury vapor, fixed with sodium thiosul-fate and coated with gold chloride. Theprocess was labor-intensive not only for

    the photographer but also for the subject:Whenever you see daguerreotypes ofchildren, you can almost hear dad in thebackground saying, You better not move,I paid $25 for this! Miller said.

    Daguerreotypes were popular forabout 20 years. They were replaced bycheaper and easier photographic tech-niques after 1860. Of the 20 million madebetween 1840 and 1860, several thousandare in museums. The silver sulfide, or tar-nish, that is found on daguerreotypes canbe cleaned using lasers.

    For the most part, Miller used LIBS tostudy the composition of daguerreotypesurfaces. He also used laser Raman andlaser-ablation mass spectrometry, albeitto a lesser extent, for the same purpose.Cleaning is usually done at lower laserpowers, without a visible spark, whichcould damage rather than clean the sur-face. The cleaning process can be calledlaser ablation, desorption or vaporiza-tion; it is a gentler process than LIBS,Miller said.

    Miller calls the daguerreotyperesearch sandbox science because it felt to him more like a hobby than a job.Michael Gresalfi, a co-worker at OakRidge and an amateur collector ofdaguerreotypes, introduced Miller tothe idea of laser cleaning after attendingan annual meeting of the DaguerreianSociety, which unites people from aroundthe country who are interested in the art form.

    Millers research has been published in peer-reviewed scientific journals such as the Journal of Cultural Heritage,the Journal of Imaging Science andTechnology and Applied Spectroscopy. Itwas extremely fascinating. [A daguerreo-type] is a remarkable thing youre hold-ing in your hand. Its living, in a sense,Miller said. Its 160 years old, but look at the resolution compared to a modernphoto. It looks great and has high resolution.

    Why lasers?Lasers have four main advantages overtraditional abrasive and chemical tech-niques for art conservation, Miller said.

    First, a laser can be selective withregards to what is being removed, Millersaid. By choosing the wavelength to correspond to the absorption of the

    18 Optics & Photonics News September 2004

    LASERS AND ART CONSERVATION

    Daguerreotype of the south side of the White House, probably taken in the winter of 1846during President James K. Polks administration. [Library of Congress, Prints & PhotographsDivision; reproduction number DLC/PP-1972:R01.2; photographer: John Plumbe.]

  • September 2004 Optics & Photonics News 19

    undesirable layer, one can in principlelimit the removal of any other layer withlower absorption. For instance, removingblack soot from marble could be self-limiting in that the removal stops whenthe lighter surface of the stone emerges.

    Also, real-time monitoring of lasercleaning is possible. If one monitors theemission from the laser surface interac-tion zone, that emission will changewhen the laser breaks through the lastlayer of the undesirable contaminant.The emission is then characteristic of theunderlying surface and the operatorknows to stop the laser cleaning or atleast slow down and be careful.

    A third advantage is that spot cleaningby laser is possible, offering more preci-sion than traditional techniques, such asimmersion in a solvent, or treatment of alarger area than is desired. If a fiber opticwand is used, the light can be directedinto hard-to-reach parts of an item orinto crevices, Miller said.

    Finally, if the laser power, distance ofthe laser, laser pulse rate, movement ofthe sample, and monitoring of the clean-ing is controlled by computer, then thecleaning process can be exquisitely deli-cate, comparable to computer-controlledrobotic surgery, Miller said.

    The interface of art and science is afascinating area, Miller said. The oppor-tunity to work with art conservation pro-fessionals opened the door to an entirelydifferent culture than that of the typicallyhard-science oriented community.

    Miller jokes about the interestingmix at art conservation conferences,where the laser scientists drink beer atone table and the art conservators drinkwine at another.

    The art communitys perspectiveCarol Dignard is an objects conservatorat the Canadian Conservation Institute,Ottawa, one of the largest art conserva-tion labs in North America. She agreeswith Miller that laser techniques are stillexperimental and that caution is neces-sary. All museum or heritage objectshold valuable information within theirshape and material composition, whichspeaks of the artist or craftsperson whomade them, and of the people who usedthem or to whom these objects werevaluable, Dignard said.

    In cleaning art, a conservator is boundby a professional code of ethics to usetechniques that are not abrasive and donot change the original surface color,appearance, texture, and composition.For now, laser cleaning is still to somedegree at a developmental phase. Thereremains much ongoing research,Dignard said.

    In addition to concerns about thesafety of the procedures, cost is a factorfor some museums. Sarah Wagner, for-mer senior photo conservator for theNational Archives and now in privatepractice, says a $100,000 laser would putquite a dent in the equipment budgets of smaller museums. Its not somethingpeople are opposed to in an anti-technol-ogy sense, but the costs of lasers wouldneed to drop to be commonly used. Itslike wanting to buy a plasma televisionbut waiting to spend $300, not $3,000,Wagner said.

    Meg Abraham, a laser researcher atAerospace Corp. in Los Angeles, alsoworks on the staff of the Los AngelesCounty Museum of Art, the only U.S.museum with an in-house laser lab.Abraham is one of the few laser scientistsin the country working for a museum.

    She has used Raman spectroscopy to study netsuke, intricately carved,ivory jewelry that is part of traditionalJapanese dress.

    Abraham notes that YAG lasers arethe real workhorse in the industry. Withprices of YAG lasers coming down, theycould be used for cleaning marble andstone. Abraham tested a generator-operated YAG laser to clean graffiti offboulders in Oregon at a national park.European art conservators use YAG lasersextensively to clean industrial pollutionoff marble statues and buildings, in partbecause they simply have more marbleart, Abraham said. But excimer lasers,necessary for cleaning more delicatepaintings, will not be cheaper in thenear future, she said.

    Still, Miller is optimistic about thefuture of laser-based art conservation.I hope that more conservation labs will acquire lasers and begin training staffto experiment and evaluate the usefulnessof the laser tool compared to traditionaltechniques. Over time, I believe that itwill prove to have important and uniquecapabilities.

    Daniel Dawes (ddawes@osa.org) is a member of theeditorial team in OSAs publications department.

    LASERS AND ART CONSERVATION

    The interface ofart and science is a fascinating area.The opportunity to work with artconservation professionalsopened the door to an entirely different culturethan that of thetypically hard-science orientedcommunity.

    John MillerU.S. Department of Energy

    Tell us what you think: http://www.osa-opn.org/survey.cfm

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