The Radiography of Panel Paintings by Electron Emission Author(s): Charles F. Bridgman, Sheldon Keck and Harold F. Sherwood Source: Studies in Conservation, Vol. 3, No. 4 (Oct., 1958), pp. 175-182 Published by: Taylor & Francis, Ltd. on behalf of the International Institute for Conservation of Historic and Artistic Works Stable URL: https://www.jstor.org/stable/1505008 Accessed: 02-05-2020 13:25 UTC REFERENCES Linked references are available on JSTOR for this article: https://www.jstor.org/stable/1505008?seq=1&cid=pdf-reference#references_tab_contents You may need to log in to JSTOR to access the linked references. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected] Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at https://about.jstor.org/terms Taylor & Francis, Ltd., International Institute for Conservation of Historic and Artistic Works are collaborating with JSTOR to digitize, preserve and extend access to Studies in Conservation This content downloaded from 188.8.131.52 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms CHARLES F. BRIDGMAN, SHELDON KECK and HAROLD F. SHERWOOD The Radiography of Panel Paintings by Electron Emission Received 19/5/58 materials are irradiated with very penetrating X-rays, they emit electrons.' The intensity of RADIOGRAPHIC examination of paintings is not new; in fact, shortly after RSntgen discovered X-rays in 1895, radiographs were being made of paintings [I]. Improvements in X-ray equipment and films and an understanding of the technical problem involved have facilitated the examination of paintings on canvas and the interpretation of radiographs. However, difficulty has been encountered in the rr' 44; radiography of panels fitted with wooden cradles on the backs to prevent warping (Figs. I and 2), as well as those on panels that might be as thick as 1I inches with paintings on both sides. X-rays are absorbed to varying degrees by everything they traverse-the layers of paint and ground, the wooden panel, and the cradle. In the radiograph (Fig. 3) we see much of the image of the portrait; however, superimposed on this is the structure of the wooden panel with the twisting wormholes filled with lead. There is also the image of the structure of the cradle with alternate rectangular areas denser than the others. These are caused by the spaces between the battens of wood forming the cradle. It can readily be seen how these images of the panel and cradle interfere with complete visualization of the image of the paint layer. Methods have been devised to eliminate FIG. I. Reverse of panel showing cr holes, and painted accession num 1The various methods of analysis these unwanted images. One has employed an may be briefly described as follows: arrangement whereby the film and painting Conventional radiography-A photo are moved during the X-ray exposure in such a manner that the image of the cradle is blurred more than that of the pigment . We have approached the problem from a different direction, based on the fact that when produced by the differential absorp they pass through a specimen. Electron emission radiography-Und tion, the various elements in a specim intensities of electrons. These elec graphically recorded to produce an 175 This content downloaded from 184.108.40.206 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms 176 C. F. Bridgman * S. Keck * H. F. Sherwood -:: . ! :. :..- - -- - ---. --- .------ --- ? i?. . ? . .. ?ii~iii ~ .. . . . . .........: .... . ...... . : ..4. ?":..... ::.......... J i'": . ...,......... : ..... ,, :l!ii":i:;;i," i ?~ T:1i ...,." -1.N , ':":" --MM , .... . .:.... 24.. :. t .....: .". ." i'ni% N i. -M ? '.i: ? .,: i...... N-V .. . . "V '3! "n,,;,,N FIG. 2. 'Portrait Brooklyn Photograph X-ray of Museum C made diffraction--The this emission depends upon the material. It is c specimen deflect X-ray negligible for light elements, such as carbon, angles. The pattern of but increases as the atomic number of the sub- s characteristic of the part stance increases. Thus, pigments differing in X-ray fluorescence anal composition, such as lead carbonate, zinc oxtion, elements emit spec escence X-rays. ide, chromiumAnalysis oxide, or mercuric sulphide, o some of the elements will differ in their electron emission when in tion. irradiated. These electrons in turn will affect The present paper is concerned only with the second of these methods. a photographic film in contact with the pig- ments. This content downloaded from 220.127.116.11 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms Radiography of Panel Paintings by Electron Emission 177 ..... .. ... .. . ~~KA A .. ....... .. . . . .. i.1A 'Al -X Z-? IF~ ee:. ICw e,-W . . . . ...... . .... . .. . .. . It ACM ED r A? 0 FIG. 3. Radiograph wormholes, and acc its losses. The use of this method has been helpful in many fields, such as metallurgy and phi- lately [31. Even the design on a postage stamp will emit electrons if the printing ink contains heavy metallic pigments. The electron radiograph of the little portrait is most enlightening (Fig. 4).1 Not only is the 1The electron radiograph is printed as a positive image so that it will be easier to interpret alongside the standard X-ray image, which is a negative. image of the cradle entirely absent, including the accession number painted on it, but also the image of the panel with its filled wormholes. The brushwork of the ground, as well as of the paint layer, appears to be recorded. Note the horizontal brushstrokes which are completely continuous from left to right, extending throughout the entire painting, background, hat, face, beard, and garment. These seem to be caused by irregular horizontal AA This content downloaded from 18.104.22.168 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms 178 C. F. Bridgman * S. Keck * H. F. Sherwood ........ .. .. .......... ... .. . .. . . .. ...... .... FIG. 4. Electron are not recorde densities in the as well a be the image of A photo lar thicknesses i the exte the paint layer for com both large and (Fig. 4) irregular areas blac of materials of low indicatio After the rad due to t the painting w employ routineorigina proced emission dition of the p removal excepti of the This content downloaded from 22.214.171.124 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms Radiography of Panel Paintings by Electron Emission I79 ,iiiiN " [!..: .i, :: ::iiiii'i liiHii i : ?':'ii; ; ? . .... :: i ? .. :[ .:..... . *..? ? + ? ., .:? .i . ? ?;-. ? ? a:; ai: .0 . ... . . . . . . :: ....'~ll,:., i:,,_?;;;;" ........ 3 i .. .:i:% ., " ..::.... ?.iil~: ? ?' ' ?:::?:- i 1::".: : .. "i;~l:ii'i . [! ? ?.ii.. ?. ?...::" :i~i~~ir : .i! ?iiii ?:~:.ii . ? ::..! i l i~ :.- iii:;i FIG. 5. P may be These amined for cleavages, loose ar paint, or for exte radiogra sive worm tunnels which might cause collaps the of paint under rest vacuum. If it is free of these de compose fects, it is considered safe to proceed. With sheet of X-ray film on the paint surface, it TECHNIQUE then placed in the open end of the bag in th In as much as the bare film must be in intidarkroom. The open end of the bag is closed mate contact with the surface of the painting, rolled, and clamped. After this, the bag a large, light-tight bag of black vinylcarefully plastic carried into the exposure room an was devised with a fitting for the attachment of centered with respect to the X-ray tube (Fig 6). The a vacuum line . The painting is first ex- photographic effect of the primar This content downloaded from 126.96.36.199 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms I8o C. F. Bridgman * S. Keck * H. F. Sherwood w.Ma? .. ......... ... .... . .. ............ ... ... -z EV -Vgz SE Zr i'W 11..I FIG. 6 radiati sev mov electro by the wh with t elec X-rays exp face, b 40tion at the tube. Kodak No-Screen Medical the act to X-rayenh Film was used. vacuum is prod SUMMARY ment l cessive The utilization of electron emission r unnece than X-radiation makes it possible to Electro satisfactory images of the paint layers o penetr ings. Images obtained from electron betwee cannot supplant those formed by X-r 1 The authors do not know of any instances whereby However, the technique is particularl paintings have been damaged by X-radiation, although on panels which are thick for paintings such might be a possibility. Chemical changes may be heavy reinforcement. produced by penetrating radiation, but such a reaction The image created by X-radiation generally requires a dose many orders of magnitude will reveal information greater than that used for elecz:on emission radiography. This content downloaded from 188.8.131.52 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms concerning n Radiography of Panel Paintings by Electron Emission 181 :; ..:? .[:. i: ... ? :: ":::..I:.i N., .i :..: .. : .. .ii ? :. ? lid .... N 4- . . .. .::. .:'N-.' N , . :: : z:... 4:R.......... . ...: . . . .. . . M : .::. i~~~Iii ;.:!ii ? .. .. ..:::.: : NE.: : :.j :.,::::.... ..mm ..........~ ~ :ti~i iil i igiixi: -i: ? .. !tilill N ....:... 4 ::.A Tu 5 :::: s., x-. . . ?. . "p. %"::, N4.. - .: n! iti i: i i:;i:l;!i iN;/iii :l N:: ::? :: ii~~. :s:grg':' ... ::l~a~iij N. N No .'si ?:?i~*::?i si"iiEi~i B 4 N ':x'i s: N~-:1. ::::x .. . .. . .. . Fi, Ux.? -:: 4 ..... ... ? i:. .... Ei "!III. N.. -XI ?;Fif, N? . . ... .. ... is; : FIG. 7. On the left side of this electron radiograph a sheet of paper has been interposed between picture and film. This absorbs all electrons, leaving only the very faint primary X-ray image that is also produced. (Negative image.) the pigment layer or layers but alsoHowever, the sup- this is merely conjecture an specific rule can be established. port, whether it be canvas or wood. The image obtained from electron emission (Fig. 4), on CHARLES F. BRIDGMAN the other hand, reveals information concerning SHELDON KECK only the paint layer. If the paint layer is very thin and low in density, electronsEastman from an Kodak underlying pigment layer might conceivably Rochester 4, penetrate it and record an image on N.Y., the U.S.A. film. HAROLD F. SHERWOOD Co., This content downloaded from 184.108.40.206 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms 182 C. F. Bridgman * S. Keck * H. F. Sherwood References I Editorial. Electrical Rev., London, 30 April, 1897. 2 PEASE, M., 'A Note on the Radiography of Paintings', The Metropolitan Museum of Art Bulletin, Iv, pp. 136-9, No. 5. 3 POLLACK, H. C., BRIDGMAN, C. F., and SPLETTSTOSSER, H. R., 'The X-ray Investigation of Postage Stamps', Medical Radiography and Photography, xxxI, pp. 74-8. 4 SHERWOOD, H. F., 'Vacuum Exposure Holder for Microradiography', Review of Scientific Instruments, CCCxvnI (1947), pp. 80-3. LA RADIOGRAPHIE DE PEINTURES SUR PANNEAU PAR EMISSION ELECTRONIQUE Resume L'emploi d'dmissions 6lectroniques plut6t quel'image produite par emission 6lectronique de rayons X rend possible l'obtention d'images(Fig. 3) ne fournit que des renseignements satisfaisantes de la couche picturale des tab- sur la seule couche picturale. Si celle-ci est leaux. Ces images ne remplacent pas cellestris mince et a faible densit6, des 6lectrons obtenues " partir des rayons X, mais cetteissus d'une couche pigment&e sous-jacente pourraient le cas 6cheant pin6trer dans la technique est particuli&rement utile pour des panneaux 6pais ou fortement consolides. couche picturale et former une image sur le L'image fournie par les rayons X (Fig. 2)film. Ceci, cependant, n'est qu'une simple condonne des renseignements non seulement surjoncture, et on ne peut 6tablir de regle fixe. la (les) couche(s) pigmentie(s) mais aussi sur le support en toile ou en bois. Par contre, This content downloaded from 220.127.116.11 on Sat, 02 May 2020 13:25:28 UTC All use subject to https://about.jstor.org/terms C. F. B. S. K. H. F. S.