Some 27 letters with secret messages written in urine, sent from the women’s concentration camp in Ravensbruck with information about medical experiments conducted on prisoners, have been gifted to a small museum in Poland where they will undergo preservation work.
The collection of the letters, gifted to the “Under the Clock” Martyr Museum in Lublin, in eastern Poland, came from the family of one of its authors, Krystyna Czyz-Wilgat.
Secret messages were written in urine using a thin linden stick. As a result of an acid reaction with the paper, the urine lost its color after a short time and became invisible.
In order to reveal the encrypted message it was necessary to heat up the letters. In the first letter that was sent there was a clue that the next letters will be written with urine.
“The next letters were read properly, how? The letters were ironed and the writing turned brown,” explained Barbara Oratowska, the curator of the museum.
Thanks to the encrypted messages, a list of 74 women from Lublin that were subjected to medical experiments by Nazi doctors in Ravensbruck, such as being injected with gangrene to test new drugs, eventually became public knowledge.
“There, in the German camp the experiments were carried out by German doctors with professor titles,” Oratowska said.
“Even though there were broad reports about the Auschwitz camp, on Ravensbrück there were was little information released. And only those female Poles were the ones who conveyed this information. That is why these letters are such a valuable material and historic evidence,” she added.
The letters, sent between 1943–1944 from Ravensbruck, a German concentration camp 50 miles (80km) north of Berlin, had messages written in urine between the lines and in the margins of regular letters to families, which were censored.
Oratowska said some of the letters were in a poor condition and needed preservation work. It is unknown whether and if they will be on a public display.
Between 1939 and 1945 some 130,000–132,000 female prisoners passed through the Ravensbruck camp, with a third of them being Polish.