Technology & Science

'Spy lab' decodes disappearing ink

A U.S. historian and chemist have teamed up to crack an old mystery: the formula the East German secret police used to make invisible ink.

A U.S. historian and chemist have teamed up to crack an old mystery: the formula the East German secret police used to make invisible ink.

"Secret writing is a classic method of communication for spies," Kristie Macrakis, a historian of science at Michigan Statue University, said in a release Wednesday. "This is a high-level formula. It's not just lemon juice. It's much more sophisticated."

Macrakis discovered a partial formula in the archives of the East German secret police, the Stasi, after the fall of the Berlin Wall in 1989.

Sheapproached chemist Ryan Sweeder, a colleague at MSU's Lyman Briggs School of Science, to see if they could crack the ink code.

"We wanted to decipher the question marks in the formula. We knew nothing about amounts and concentrations," Sweeder said.

Working in a room dubbed the "spy lab" with undergraduates, the researcher found the missing links.

The Stasi used a system in which an agent would put a piece of paper impregnated with the chemical cerium oxalate between two pieces of plain paper. As the agent wrote on the top piece, the chemical was pressed on to the bottom piece.

The bottom piece was sent to another agent, who useda solution of manganese sulfate, hydrogen peroxide and other chemicals to activate the cerium oxalate to reveal the hidden text. If the process worked, orange writing appeared.

"From a chemical standpoint, this is very cool," Sweeder said.

The Stasi, the East German secret police, was formedin 1950and closely allied with the Soviet secret police. It was reputedly one of the most efficient secret forces in the world.

It hadtens of thousands of employees anda huge network of informers. Bytime East Germany collapsed, the Stasi had secret files on 2.4 million people, one out of every seven people in the country.