LABORATORY EXPERIMENT pubs.acs.org/jchemeduc
An Investigation into the Creation, Stability, and X-ray Fluorescence Analysis of Early Photographic Processes: An Upper-Level Undergraduate Laboratory Corina E. Rogge*,†,§ and Aniko Bezur‡ † ‡
Department of Chemistry, Rice University, Houston, Texas 77251-1892, United States The Museum of Fine Arts Houston, Houston, Texas 77265, United States
bS Supporting Information ABSTRACT:
Photography is one of the few fine art forms that were initially developed by scientists such as Herschel and Talbot; however, in the modern chemistry curriculum, photography has become divorced from its scientific beginnings and resides in the studio arts department of most universities. An upper-level undergraduate experiment is described in which students duplicate William Henry Fox Talbot’s original silver-based photographic methods and analyze their prints by X-ray fluorescence spectroscopy. The students are able to successfully make prints and experimentally confirm whether the prints had been halide stabilized, thiosulfate-fixed, or toned with sulfur, selenium, or gold. Their experimental results are discussed in the context of preservation of museum collections and photograph conservation. This experiment introduced students to the field of conservation science, where chemistry is applied to the investigation and preservation of artistic or cultural materials, activities that often involve the re-creation of historic techniques. KEYWORDS: Upper-Division Undergraduate, Analytical Chemistry, Inorganic Chemistry, Interdisciplinary/Multidisciplinary, Laboratory Instruction, Hands-On Learning/Manipulatives, Applications of Chemistry, Fluorescence Spectroscopy, Oxidation/ Reduction, Photochemistry
R
In the 1830s, William Henry Fox Talbot began attempting to produce photosensitive paper by in situ formation of silver chloride;14 he first soaked the paper in an aqueous solution of sodium chloride and subsequently brushed on an aqueous silver nitrate solution:
ecent trends in chemical education have emphasized the cross-discipline connection between chemistry and art as a means of introducing students to a “hard” science. Several excellent articles outlining courses and laboratory experiments have been published in this Journal,113 but they have primarily focused on introductory courses and material. A two-period (4 h per period), upper-level undergraduate laboratory is presented that emphasizes the connection between chemistry, conservation science, and museums through the re-creation of historical photographic images and their analysis by X-ray fluorescence spectroscopy (XRF). The chemistry of silver(I) salts is a rich area involving photochemistry, oxidationreduction, complex ion formation, and solubility and precipitation equilibria. This intersection of chemistry and photography is a largely unexplored area for students, many of whom have never used anything other than a digital camera. Copyright r 2011 American Chemical Society and Division of Chemical Education, Inc.
AgNO3 ðaqÞ þ NaClðaqÞ f AgClðsÞ þ NaNO3 ðaqÞ
ð1Þ
Upon exposure to light, these papers darkened owing to metallic silver formation, allowing the shadow or photogenic drawing of an object to be captured: 2AgClðsÞ þ hν f 2AgðsÞ þ Cl2 ðgÞ
ð2Þ
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However, the papers remained photosensitive and the darkening process could not be halted. Through observation, Talbot noted that lower concentrations of halide led to more photosensitive papers; he, thus, could photosensitize papers using low concentrations of chloride, but then stabilize the exposed print by immersing it in an aqueous solution with a higher concentration of halide, either chloride, iodide, or bromide. Communication with another early photographer, Sir John Herschel,15 led him to try removing unexposed silver halide with sodium thiosulfate or “hypo” (Na2S2O3), which forms a soluble coordination compound, [Ag(S2O3)2]3 AgClðsÞ þ 2S2 O3 2 ðaqÞ f ½AgðS2 O3 Þ2 3 ðaqÞ þ Cl ðaqÞ
ð3Þ a process that came to be known as “fixing” the print. The images produced by these processes came to be known collectively as salted paper prints. Because of the inherent instability of silver with respect to oxidation, many of the thiosulfate-fixed prints were also “toned” where the silver particles are converted to more stable compounds such as Ag2S or Ag2Se or are partially replaced by more noble metals such as gold or platinum. The diversity of methodologies used to create early photographs means that museums often own photographs where the materials and their stability are only tentatively known. In one instance, this led to improper display conditions of one of Talbot’s prints and resulted in irreparable damage.16 As part of an upper-level undergraduate laboratory course investigating early photographic methods, an experimental protocol was developed that allows the students to recreate Talbot’s methods, thereby making their own salted paper prints. The stability of these prints could be assessed over the short term allowing the students to understand the limited lifetime of the objects and display and conservation issues faced by museums arising from this instability. The prints were also analyzed by X-ray fluorescence (XRF) spectroscopy to determine if this nondestructive method could accurately distinguish how the student prints were made.
’ EXPERIMENTAL DETAILS Student preparation for the lab included a handout outlining a brief history of salted paper prints and an introduction to XRF (see the Supporting Information). Before coming to lab, students were also required to read a paper outlining the use of XRF in museums.17 Students used a negative (typically a black and white transparency) to make chloride-, bromide-, and iodide-stabilized prints using Talbot’s procedure with a slight modification suggested by Alfred S. Taylor in 1839 ([Ag(NH3)2]+ instead of Ag+ was reacted with NaCl) as outlined by Mike Ware18 using contact printing frames.19 They then utilized the same negative to make thiosulfate-fixed prints using a multistep procedure involving a prefixing bath, fixing with thiosulfate, and then a final wash.20 The thiosulfate-fixed prints were toned using commercially available Kodak sepia (sulfide) or selenium toners, or Clerc’s thiourea gold tone.21 Use of the same negative for all prints allowed a more direct comparison of final image tone, an important clue photograph conservators use to identify processing technique. The finished prints were analyzed spectroscopically using a Tracer III-V (Br€uker AXS) handheld XRF instrument (15 kV accelerating current, 15 μA anode current, 180 s of live collection
Figure 1. Bromide-stabilized salted paper print from an antique glass negative. Vertical lines that look like folds are tidelines caused by diffusion of the silver nitrate solution after the paper is brushed with the solution.
time) equipped with a vacuum adaptor to enhance detection of chlorine and sulfur. Because of the difficulty in quantitatively determining concentrations and also to better illustrate how the instrument is actually used within a museum setting, relative peak intensities were compared rather than quantifying relevant elements.
’ HAZARDS Appropriate eyewear and protective equipment should be worn at all times. Silver nitrate, ammonium hydroxide, and hydrogen tetrachloroaurate(III) hydrate are corrosive and poisonous and should be handled with care. Kodak Professional Sepia II Warm Toner kit contains potassium ferricyanide, which releases cyanide gas upon exposure to acids. Potassium iodide and sodium thiosulfate are skin and respiratory tract irritants. The instructors had previously obtained radiation safety training and were conversant with safe operation of the X-ray fluorescence instrument. The instrument was positioned so to avoid accidental exposure of students to radiation and the students were monitored at all times during instrument use. Additional guidelines and safety measures are provided in the Supporting Information. ’ DATA ANALYSIS AND RESULTS The students produced both halide-stabilized and thiosulfatefixed prints with no difficulties (Figure 1). Halide-stabilized prints were visually distinguishable with chloride, bromide, and iodide having violet-, gray-blue-, and yellow-colored highlights, respectively; accurately reproducing Talbot’s results.14 Unexpectedly, the iodide-stabilized prints were the most unstable, with one print reoxidizing back to silver iodide over a period of a few days.18 Another iodide-stabilized print was not soaked in the potassium iodide stabilization solution for long enough, resulting in a print that remained photosensitive; over a few hours, the highlight areas darkened to a violet color due to formation of silver particles within the silver chloride crystals.22 These incidents aptly demonstrated to students the extreme vulnerability of early photographic prints, highlighting challenges faced by conservators with regard to handling and exhibition of such 398
dx.doi.org/10.1021/ed101185d |J. Chem. Educ. 2012, 89, 397–400
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Table 1. Relative Intensity of XRF Peaks Arising from Image Materials in Salted Paper Printsa Print Type
Ag
Cl
Br
Chloride stabilized
++ ++++ -
Bromide stabilized Iodide stabilized
++ ++ -
Thiosulfate fixed, sulfide toned
I -
S Se Au -
-
-
++++ ++++ -
-
-
++ -
-
-
+
-
-
Thiosulfate fixed, selenium toned ++ -
-
-
+
+
-
Thiosulfate fixed, gold toned
-
-
+
-
+
++ -
a
A single dash (-) indicates that the element was not detected. Plus signs (+) indicate the relative peak height of the detected element, based upon peak height, with (+) being very small and (++++) being very large.
Figure 2. XRF spectra of salted paper prints: (A) halide-stabilized prints and (B) thiosulfate-fixed and toned prints. Peaks arising from the imaging materials or, in the case of rhodium, from the instrument are indicated. Other peaks are due to the paper support.
prints. Visual inspection could also help distinguish between untoned thiosulfate-fixed prints and those toned by sulfide or selenide; but accurately distinguishing between the two toners was difficult. Likewise, visual inspection was unable to determine whether a thiosulfate-fixed print was gold-toned. XRF analysis was able to accurately determine how the prints were stabilized or fixed and toned. The prints were analyzed in their darkest-dark regions where the most image and toning materials are located. After obtaining the spectrum, the element of interest is selected and the program highlights the expected K, L, or M peak positions allowing the students to easily determine if the selected element is present. The chloride-stabilized print displayed an intense KR peak and a Kβ peak that was overlapped by the silver L peaks. The bromide-stabilized prints had intense
KR and Kβ peaks well separated in energy from other peaks, whereas the iodide-stabilized prints displayed the expected iodine L lines, iodine K electrons having too high an ionization energy to be ejected by the XRF instrument (Table 1 and Figure 2A). Residual chloride could not be detected in the latter two print types due to masking by rhodium L peaks arising from the instrument. Thus, XRF spectroscopy readily identified the halides responsible for stabilization in salt-stabilized prints. All thiosulfate-fixed prints displayed sulfur peaks due to the incomplete removal of thiosulfate during the final wash (Figure 2B); thus, determination of sepia toning by XRF alone is difficult. Selenide- and gold-toned prints were accurately identified by XRF analysis as the peak arising from the overlapping Se KR and Kβ lines was seen in the former and Au LRa peak was observed in the latter. As fixing with thiosulfate removes unreduced silver from the highlight areas of the print, additional confirmation of halide stabilization versus thiosulfate fixing came from comparison of the highlight area spectra. Thiosulfate-fixed prints displayed little to no silver in the highlight areas, whereas halidestabilized prints displayed relatively equal quantities of silver in dark and highlight areas.
’ DISCUSSION This lab was well received by the students for several reasons, including their surprise at obtaining high quality images using a historical technique, something that few of them had done in this age of digital photography. Because the students were able to choose between a wide variety of stabilization, fixing, and toning methods, they were more invested in the experience and could appreciate the challenges faced by photograph conservators in print identification and dealing with stability issues. The use of XRF allowed students to learn a new analytical method capable of nondestructive surface elemental analysis and aptly illustrated how this technique can play an important role in museums, an aspect of science to which most students are not exposed. Finally, the field of photograph conservation is a relatively new and unpopulated area and this, combined with the close collaboration with the Museum of Fine Arts Houston, allowed the students to feel as if they were making a real contribution to the museum community. From an instructor’s standpoint, this was also a satisfactory lab; apart from the XRF instrument all chemicals and materials are readily available. Many art museums have XRF units and may be willing to collaborate, and as pointed out in another recent article, there are many rental companies that supply XRF units so instrumentation should not be an insurmountable problem.23 During the laboratory time, different aspects of photographic chemistry were discussed, which served to reinforce classroom learning. With the use of the XRF unit, the students were able to accurately identify methods of image manufacture and analysis of the prints became a collaborative effort within the group, increasing peer learning. ’ ASSOCIATED CONTENT
bS
Supporting Information Instructions for the students and notes for the instructor. This material is available via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION Corresponding Author
*E-mail: roggece@buffalostate.edu. 399
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Present Addresses
(19) Barnier, J. Coming into Focus: a Step-by-Step Guide to Alternative Photographic Printing Processes; Chronicle Books: San Francisco, CA, 2000. (20) James, C., The Book of Alternative Photographic Processes, 2nd ed.; Delmar Cengage Learning: New York, 2009. (21) White, W. A Dash of Salt. In http://www.alternativephotography.com/wp/processes/saltprints/a-dash-of-salt (accessed Jun 2011). (22) Ware, M. Quantifying the Vulnerability of Photogenic Drawings. In Research Techniques in Photographic Conservation: Proceedings of the Conference in Copenhagen, 1419 May 1995; The National Museum of Denmark: Copenhagen, 1995. (23) Bachofer, S. J. Sampling the Soils Around a Residence Containing Lead-based Paints: An X-ray Fluorescence Experiment. J. Chem. Educ. 2008, 87, 980–982.
§
Department of Art Conservation, Buffalo State College, Buffalo, New York 14222, United States.
’ ACKNOWLEDGMENT The work discussed here formed a component of the laboratory module “The chemistry and scientific examination of historic photographic techniques” co-taught by the authors in 2009 in the Department of Chemistry at Rice University. At the time, C.E. Rogge was Wiess Instructor of Chemistry. The authors wish to acknowledge the support of the Department of Chemistry for the realization of the laboratory module. The Museum of Fine Arts Houston generously allowed use of their XRF spectrometer, the purchase of which was made possible by a 2007 grant from the Institute of Museums and Library Services. We thank Toshiaki Koseki, photograph conservator at the Museum of Fine Arts Houston, for his time, advice, and generously allowing us to use the XRF unit. A. Bezur's position at the Museum of Fine Arts, Houston, was supported by a grant from the Andrew W. Mellon Foundation. ’ REFERENCES (1) Jacobsen, E. K. JCE Resources for Chemistry and Art. J. Chem. Educ. 2001, 78 (10), 1316–1321. (2) Kafetzopoulos, C.; Spyrellis, N.; Lymperopoulou-Karaliota, A. The Chemistry of Art and the Art of Chemistry. J. Chem. Educ. 2006, 83 (10), 1484–1488. (3) Greenberg, B. Art in Chemistry: An Interdisciplinary Approach to Teaching Art and Chemistry. J. Chem. Educ. 1988, 65 (2), 148–150. (4) Beilby, A. L. Art, Archaeology, And Analytical Chemistry: A Synthesis of the Liberal Arts. J. Chem. Educ. 1992, 69 (6), 437–439. (5) Friedstein, H. G. A Short History of the Chemistry of Painting. J. Chem. Educ. 1981, 58 (4), 291–295. (6) Orna, M. V. The Molecular Basis of Form and Color. A Chemistry Course for Art Majors. J. Chem. Educ. 1976, 53 (10), 638–639. (7) Orna, M. V. Chemistry, Color, and Art. J. Chem. Educ. 2001, 78 (10), 1305–1311. (8) Uffelman, E. S. Teaching Science in Art. J. Chem. Educ. 2007, 84 (10), 1617–1624. (9) Scaccia, R. L.; Coughlin, D.; Ball, D. W. A Microscale Synthesis of Mauve. J. Chem. Educ. 1998, 75 (6), 769. (10) Gettys, N. S. Pigments of Your Imagination: Making Artist’s Paints. J. Chem. Educ. 2001, 78 (10), 1320A–1320B. (11) Lawrence, G. D.; Fishelson, S. Blueprint Photography by the Cyanotype Process. J. Chem. Educ. 1999, 76 (9), 1216A–1216B. (12) Abrahamson, H. B. The Photochemical Basis of Cyanotype Photography. J. Chem. Educ. 2001, 78 (3), 311. (13) Ware, M. Prussian Blue: Artists’ Pigment and Chemists’ Sponge. J. Chem. Educ. 2008, 85 (5), 612–621. (14) Talbot, W. H. F. An Account of the Process Employed in Photogenic Drawings. Abstracts of Papers Printed in the Philosophical Transactions of the Royal Society London 18371843, 4, 124–126. (15) Schaaf, L. J. Records of the Dawn of Photography: Talbot’s Notebooks P & Q; Cambridge University Press: Cambrige, 1996. (16) Rheinhold, N. The Exhibition of an Early Photogenic Drawing by William Henry Fox Talbot. Topics in Photographic Preservation 1993, 5. (17) Glinsman, L. D. The Practical Application of Air-path X-ray Fluorescence Spectrometry in the Analysis of Museum Objects. Rev. Conserv. 2005, 6, 7–21. (18) Ware, M. Mechanisms of Image Deterioration in Early Photographs: The Sensitivity to Light of W. H. F. Talbot’s Halide-fixed Images 18341844; Science Museum and National Museum of Photography, Film and Television: London, 1994.
’ NOTE ADDED AFTER ASAP PUBLICATION This paper was published to the Web on July 8, 2011, with an error in Figure 2. The corrected version was published to the Web on January 20, 2012. ’ NOTE ADDED AFTER ISSUE PUBLICATION Changes have been made to the corresponding author information and the acknowledgment after this paper was published on July 8, 2011. The revised version was published to the Web on August 14, 2012.
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