While serving in Paris as an agent of the Committee of Secret Correspondence, Silas Deane is known to have used a heat-developing invisible ink—a compound of cobalt chloride, glycerine and water—for some of his intelligence reports back to America. Even more useful to him later was a "sympathetic stain" created for secret communications by James Jay, a physician and the brother of John Jay. Dr. Jay, who had been knighted by George III, used the "stain" for reporting military information from London to America. Later he supplied quantities of the stain to George Washington at home and to Silas Deane in Paris.