I'm doing research about a chemical (prussian blue) and found out that it was apparently used to stain clothes, including uniforms of prussian soldiers. Now, prussian blue doesn't do so well when it comes into contact with soap (or bases in general). It will break apart and turn into what is essentially rust.
Are there any records of prussian soldiers having bleak uniforms after some time on the front or not wanting to wash them? I remember reading a sentence or two about it and one of my supervisors mentioned this when we talked. Is it true?
Prussian Blue is certainly degraded by alkali : it's not much good in fresco painting, because of that. I've also thought that the powder blue found in very old paint finishes might at least sometimes be due to the alkali in milk paint: but in theory that should turn it brown.
It would be nice to find a 19th c. German source mentioning unclean Prussian soldiers but I couldn't roust one out, and the few texts I found on mid 19th c. dye chemistry ( in which the Germans were very much leaders) are printed in Fraktur, and I'm afraid I read German slowly, Fraktur very slowly. However, this seems to be used as a problem question in German chemistry classes now ( "Why didn't the Prussian soldiers wash their uniforms?" ) so in Germany it looks to be at least common knowledge. It's not as solid a source as I'd like, but this one reference below to Prussian soldiers not washing their uniforms is typical. My rough translation:
Strangely enough, the soldiers never washed their blue uniforms, not because they were were particularly unhygienic - but the Berlin blue has a major weakness.... It is unsuitable for clothing because it disintegrates in an alkaline environment, and Brown iron (III) oxide hydroxide [FeO (OH)] is formed. Washing with soaps and other basic detergents is therefore not possible.
Sabine Marx, Max Waldenburger: Metall-Komplexe -Zusammenhang zwischen Struktur und Farbe anhand von Beispielen