Something I've noticed - not always but frequently enough to use the
term "often" - is how freight cars were heavily weathered in the pre-1925
or so time frame and especially so in the pre-1920 time frame. This
photo is an excellent example of cars that are very grimy - an overall
kind of grime rather than showing any 'patterns'.
The world was a whole lot dirtier in "the good old days". ;-)
- Jim B.