CIA File of the Day
Supposed Soviet Formula for Secret Ink
A CIA information report, distributed 8 February 1951, on a supposed Soviet formula for secret ink. It states that the Soviet Intelligence Service was reported to have used the formula for a covert ink in the transmission of classified information on newspapers. The report marks the information as unevaluated.
Courtesy of the CIA FOIA Electronic Reading Room. Official page: CIA FOIA Electronic Reading Room. Document PDF: cia.gov reading room PDF. Copy: Internet Archive.