David Thompson wrote:
Pressac explained the presence of blue staining in the disinfestation chambers by saying that, in the disinfestation process, clothes, etc. were exposed to heavy concentrations of the Zyklon b for long periods of time -- 10-16 hours. However, Pressac says, in the homicidal gas chambers the gas only took 10 minutes or so to kill the folks inside, after which time it was pumped out.
The above would only apply to homicidal gas-chambers that had an air-extraction system.
A building that had been designed as a morgue, as for example the large room in Crematorium I, had such a system to remove the decomposition gases emanating from the stored corpses; that is what enabled the conversion of the space to a homicidal gas chamber.
By contrast, neither Bunker I nor Bunker II had such systems. According to the testimony of surviving members of the prisoner Sonderkommando serving those buildings, the homicidal gassings were carried out in the evening. The chambers were left closed all night, containing the bodies of the victims and the HCN-laden air. In the morning the chambers were opened on either side, and the HCN-laden air was vented out by the natural airflow through the building, which took some time.
In other words, the normal methodology for delousing a building or objects had been adapted for homicidal gassing. The walls of the chamber would have been exposed to the HCN for several hours, and presumably would have started to show the blue staining. However, neither of the two buildings survived.
So far as I know, neither Crematorium IV or Crematorium V had air-extraction systems, the gas being removed by natural ventilation, which took some time. So the staining might have started to develop on the inside wall of those buildings.