Hi PD's...Robert ..there are hundreds of snaps of 'turn of the century' old paddlers belching volumes of black smoke in various publications..

...mind you they hadn't thought of bodies like the Environmental Protection Group....

I think Polish coal is brown coal which is a smokey burner...where as black coal is cleaner.......I am sure any reader with naval knowledge could remind us of WW1 stories & snaps of clean burning coal to avoid detection over the horizon from that tell tale smoke plume
Here is a snap of PS Eagle doing one of her stage shows .......these early boilers were normally aspirated ie., no forced draft boiler fan....so the burning/combustion efficiency would have been low.........Derek