The Brownstone Chronicles, Part 11: Black Crusting and Spalling, the Chicago Club, the Loop, Chicago, Illinois, USA (1929)
(Updated May 14, 2024)
As I write this, the Chicago region is blanketed by a pinkish-yellow haze (official Air Quality Index = 194, rated "Unhealthy" and close to "Very Unhealthy" for all ages). That's the result of the much-publicized Canadian-wildfire plume descending on this part of the Midwest. However concerning this nasty air pollution is, it's a temporary condition, albeit one that heralds more disturbing changes yet to come in the climate system.
But imagine living and working in Chicago where this sort of toxic brew had to be breathed in on a daily basis. In the late nineteenth century and earliest twentieth, when bituminous coal mined in the Illinois Basin powered this city, unfiltered soot and acidic compounds found their way onto every exposed surface, and into everyone's lungs. I discuss this meaner, grittier version of the Windy City at greater length, and even quote one contemporary visitor, H. G. Wells, in my Chicago in Stone in Clay (see link at bottom).
If this is indeed plain soot rather than biofilm, I suspect much of it on the Lower-Jurassic Portland Sandstone of the Chicago Club's northeastern corner actually dates either to the Age of Bituminous Coal. Either that, or at least to the days of abundant automotive exhaust before the activation of the Clean Air Act (various provisions beginning in 1970).
Because this cladding was apparently face-bedded (tilted up 90 degrees from its original horizontal bedding plane), it's especially susceptible to a lot of peeling and spalling as it weathers. The much brighter-toned patches of stone represent fresher surfaces exposed by that spalling. They seem to be very recently exposed, but I'm sure darkening proceeds at least somewhat more slowly than it did, for reasons discussed in the previous paragraph.
To see the other photos and descriptions of this series, visit
The Brownstone Chronicles album. And for more on this specific site, see my book Chicago in Stone and Clay, described at www.cornellpress.cornell.edu/book/9781501765063/chicago-i...
The Brownstone Chronicles, Part 11: Black Crusting and Spalling, the Chicago Club, the Loop, Chicago, Illinois, USA (1929)
(Updated May 14, 2024)
As I write this, the Chicago region is blanketed by a pinkish-yellow haze (official Air Quality Index = 194, rated "Unhealthy" and close to "Very Unhealthy" for all ages). That's the result of the much-publicized Canadian-wildfire plume descending on this part of the Midwest. However concerning this nasty air pollution is, it's a temporary condition, albeit one that heralds more disturbing changes yet to come in the climate system.
But imagine living and working in Chicago where this sort of toxic brew had to be breathed in on a daily basis. In the late nineteenth century and earliest twentieth, when bituminous coal mined in the Illinois Basin powered this city, unfiltered soot and acidic compounds found their way onto every exposed surface, and into everyone's lungs. I discuss this meaner, grittier version of the Windy City at greater length, and even quote one contemporary visitor, H. G. Wells, in my Chicago in Stone in Clay (see link at bottom).
If this is indeed plain soot rather than biofilm, I suspect much of it on the Lower-Jurassic Portland Sandstone of the Chicago Club's northeastern corner actually dates either to the Age of Bituminous Coal. Either that, or at least to the days of abundant automotive exhaust before the activation of the Clean Air Act (various provisions beginning in 1970).
Because this cladding was apparently face-bedded (tilted up 90 degrees from its original horizontal bedding plane), it's especially susceptible to a lot of peeling and spalling as it weathers. The much brighter-toned patches of stone represent fresher surfaces exposed by that spalling. They seem to be very recently exposed, but I'm sure darkening proceeds at least somewhat more slowly than it did, for reasons discussed in the previous paragraph.
To see the other photos and descriptions of this series, visit
The Brownstone Chronicles album. And for more on this specific site, see my book Chicago in Stone and Clay, described at www.cornellpress.cornell.edu/book/9781501765063/chicago-i...