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57 J. Crim. L. Criminology & Police Sci. 368 (1966)
Reappraising Infrared Photography's Worth in Deciphering Erased Writing

handle is hein.journals/jclc57 and id is 378 raw text is: THE JOURNAL OF CRIMINAL LAW, CRIMINOLOGY AND POLICE.SCIENCE Vol. 57, No. 3 Copyright @ 1966 by Northwestern University School of Law Printed in U.S.A. REAPPRAISING INFRARED PHOTOGRAPHY'S WORTH IN DECIPHERING ERASED WRITING ORDWAY HILTON The author maintains a practice in the field of questioned document examination in New York City, where he has served as a consultant since 1946. Mr Hilton has served as Police Science Editor of this Journal since the 1940's, is the author of The Scientific Examination of Questioned Documents, a fellow in the American Academy of Forensic Sciences, and a member of the American Society of Questioned Document Examiners. He has been active in organizing the Second International Meet- ing in Questioned Documents, Copenhagen, August 1966, and has contributed to technical and legal publications in this country, Canada, England, and Europe. There are indications or suspicions that pencil or typewriting has been erased. How can the erased matter be retrieved? Simply make an in- frared photograph. This statement is an over simplification of pub- lished decipherment methods,' but an answer that is quickly given by many with only casual experi- ence in this field. Possibly it represents a document examination myth. Unfortunately, this simple formula does not work with clockwork regularity. After some years of careful and comparative in- vestigation both with experimental and actual case problems involving erased pencil, typewriting, and infrared absorbing inks, it is clear that infrared photography has little, if any, advantage over other photographic decipherment techniques. In theory infrared photography, or examination with infrared viewing equipment, should hold an advantage in deciphering erased pencil or type- writing because carbon and other metallic sub- stances absorb infrared, while paper and dye inks do not. It is this absorption-reflection differential which originally suggested infrared photography's special value and is the basis for its utility. Fur- thermore, certain dye inks are completely trans- parent to infrared, and for this reason it is of some unique importance in document examination. But with erased carbon based material there seems to have arisen an assumption that the absorption of carbon is greater in the infrared than in the visible portions of the spectrum. Thus, infrared photog- raphy should be highly efficient in picking up par- ' An example of published references to the use of infrared in deciphering erased writing can be found in J. A. RADLEY, PHOTOGRAPHY IN CRTAn DETECTION, Chapman and Hall, Ltd. (London, 1948), p. 158. Also PHOTOGRAPH IN LAw ENFORCEMENT, First Edi- tion, Eastman Kodak Company (1948), p. 195. ticles of carbon which have penetrated into the paper fibers. In the case of typewriting or pencil erasures, and in a measure with carbon based inks, such as India inks, the original writing substance does not penetrate the paper fibers. Unerased fragments of the original writing remain on the surface, most likely wedged into the crevices between the paper fibers. They can all be viewed visually or with magnification. Consequently, we are not con- fronted with the problem of revealing fragments hidden within the fibers. Therefore, infrared's ad- vantage, if any, must result from greater sensitivity than panchromatic or other emulsions. Compara- tive testing does not substantiate this assumption (figure 1). There are several different infrared emulsions avaliable. As with orthochromatic and panchro- matic photographic emulsions, manufacturers have built different contrast and resolving power char- acteristics into infrared films and plates. (In this country the Eastman Kodak Company is the sole producer of infrared films and plates, except for Polaroid infrared film and for Thermofax (in- frared) office copying machines. Accurate informa- tion on European manufacturers is difficult to ob- tain in the United States.) Contrast, speed, and wave length sensitivity differ.2 Experimentation with erased pencil writing and typewriting using various available infrared emulsions reveal that some give better results than other, but none con- sistently outperforms standard films, such as Eastman Panatomic-X, Eastman Contrast Pan- chromatic (or Orthochromatic) Process, or Ko- 2 Eastman Kodak Company supplies the following infrared sensitive materials: Infrared film, Infrared plates, and Spectroscopic Infrared plates, type I-N and type IV-N. These last are available only on special order and must be purchased in quantity.

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