Additional. Zyklon B was Hydrogencyanide adsorbored on diatomaceous earth and lime. Used as pellets it releases gas. The absence of prussic blue has nothing to do I think. Prussic blue needs iron and alkaline conditions.
The bricks and stone of the chambers could have iron impurities. Also iron and steel parks in the areas as well. Notably, I've never heard anyone conform or deny that the pipes and spray heads, which I assume a iron, are or are not coated with the tell-tale blue color of Prussian blue. Again, this is selectively used evidence, used by different people, in different ways, to prove and disprove the same points.
So obtained by cooking meat and skins from animals with iron powder and potassium carbonate.
Uh ... interesting bit of trivia. I believe that organic and inorganic synthesis was well developed, in Germany, by this point in time. So not really relevant.
More trivia: development of early Zyklon formulations was done by Fritz Haber, a scientist who worked for Germany's war effort in World War I. His Noble prize was contested by French and British, for his war efforts against them. He was not yet thrown out of Germany, for being Jewish, but would be, before his death.https://en.wikipedia.org/wiki/Zyklon_B#Historyhttps://en.wikipedia.org/wiki/Fritz_Haber
Historically, the compound was manufactured from organically derived nitrogenous carbon sources, iron filings, and potassium carbonate. Common nitrogen and carbon sources were torrified horn, leather scrap, offal, or dried blood.
Not at this point in time.
The HCN gas alone cannot create pussic blue.
I really don't know the reactions involved. As a kid, I easily made Prussian blue with ferric ammonium sulfate and potassium cyanate. But those are soluble salts and the reaction is in aqueous solution. Some bricks show blue color outside
the chambers, or only on parts on the inside. This is very muddled chemistry, and very, politically muddled, forensic science.
I don't think its really worth working on, given what I said at the start of this thread.