This is only partly true NazgulNazgul wrote: ↑Sat Jul 26, 2025 9:52 amThere is no iron in plaster so Prussian Blue cannot form from HCN on plaster. Bricks have iron the quantity depending on the brick. There are other factors such as moisture which determine the formation of P blue. Plasterwork would prevent any formation of prussian blue unless it was cracked or some parts removed to expose the bricks.

Really the iron content of plaster can vary, example above of a plastered wall - with plaster low in iron content. As we can see, for this reason and othes such you have mentioned, we see only minor blue staining.
However, thanks to the work done by Rudolf, we know exactly the iron contents of the plaster samples taken at Krema II demonstrating consistent iron contents with the heavily blue stained samples from other iron-rich plaster
This picture shows the interior plaster wall from the delousing chamber, and represents samples 9 and 11, with the given iron contents of the plaster samples
