The Scientific War Work of Linus C. Pauling Narrative  
Home | Search | All Documents and Media | Linus Pauling Day-By-Day
The Right Recipe
<  38  >

The goal for Pauling and his team was to create a series of inks that, before being treated with a developer, left no visual traces on the document and could only be made visible by a limited number of chemicals. From September to October 1944, Pauling assigned Dr. George Wright, William Eberhardt, and Frank Lanni to making preliminary examinations of potential methods for developing invisible inks, the specifications of which were not defined in Pauling's official reports to the OSRD. Once the preliminary tests were complete, Pauling and his team began a wide range of experiments, testing a variety of potential methods for developing secret inks.

The team began with possible protein-based inks. They applied various proteins including rabbit serum, human saliva, and homogenized milk to standard typing paper. Then, after steaming and ironing the treated page, they painted it with a mixture of ink, acetic acid, and sodium chloride. The combination of acid and ink caused the protein to darken slightly, making it legible in well-lit conditions.

In another test, the experimenters used diluted potassium iodide as an ink. After drying, the test screed was painted with gold chloride, rinsed, and then treated with a substance referred to only as "the silver physical reagent," a compound used by the Office of Censorship. Some of the test screeds were placed in the Eastman Kodak Company's "tropical room," a sealed chamber meant to mimic the temperature and humidity of an equatorial environment. There, the ink quickly decomposed, making it clear that potassium iodide was not a viable option.

Previous Page Next Page

Audio Clip  Audio: A Secret Code Developed by Pauling. August 23, 1991. (2:03) Transcript and More Information

Get the Flash Player to see this audio player.


See Also: "Outline of Method 1." February 20, 1945. 
See Also: "Further Observations on the Use of Acid Dyes for Development of Protein SW." April 24, 1945. 
See Also: "LC 4 - A Simple Method of SW Using Gelatin." November 10, 1945. 

Click images to enlarge 

Page 116
Test screed developed as part of a research program on invisible inks. November 14, 1945.


Page 1
"Progress Report, OSRD Contract Symbol No. 4990." November 1, 1944.

"A study of the interceptions of enemy agents' communications made by the Office of Censorship over the past three years has shown that many factors are involved in the recognition of such suspicious correspondence in addition to the technical problems of chemical testing for secret writing."

E.C. Pierce
May 7, 1945
Home | Search | All Documents and Media | Linus Pauling Day-By-Day