What is undeniable is that these Prussian blue stains have been caused by the use of Zyklon B. This is now known to be what was used to kill hundreds of thousands of people in gas chambers at locations such as Auschwitz Birkenau, but it was originally used as a cyanide based substance used to delouse clothes.
And this area of the camp are barracks 41, with signage indicating that this is where prisoners were gassed. However, there is some considerable argument about whether this can possibly be true, and on the camp’s own web-site there’s a document saying:
“It is certain, however, that gas chambers were not used for extermination after the executions of 3 November 1943 and that the chamber adjoining the shower room in barracks No. 41 and the chamber in the west part of the bunker were used for the disinfection of blankets and clothes, including those belonging to murdered Jews. These were disinfected using Zyklon B. First, the chamber was warmed up with heated air and, after disinfection was complete; the gas was removed through openings in the roof with the use of a ventilation fan.”
So although it’s clear that significant numbers of people were killed at Majdanek, I’m not sure that this area is where they actually were murdered. The blue stains do appear to be from when the room was used to delouse blankets and clothing, although it is possible that killings took place earlier on.
I have to admit to be entirely confused by much of the signage at Majdanek, I ended up with far more questions than answers.