The Brownstone Chronicles, Part 37: Of Corrosion, Crusts, and Case Hardening | Durand Institute, Lake Forest College, Lake Forest, Illinois, USA (1892)

A close-up of the northern side of the main entrance steps.

To see this building's entire western elevation, check out Part 33 of this series. And the building's central portion is more fully displayed in Part 34. Both of these posts discuss the geologic origins of the rock type described below.

Choose your favorite metaphor or world view:

- The Earth is a high-energy machine that is constantly breaking down and rebuilding itself.

- The Earth is a living organism that recycles its old tissues and grows new ones.

- "There’s nothing constant in the universe,
All ebb and flow, and every shape that’s born,
Bears within its womb the seeds of change."

The last of these is a translation from the Metamorphoses of Publius Ovidius Naso, better known to anyone in my own culture who still actually reads the classics as the Roman poet Ovid.

My objective in giving you this assortment of conceptualizations is to point out that in this world the act of construction is just one part of a process that must also must involve decay and destruction.

Buildings seen through a geological lens are an especially good place to learn this. Some architects, particularly those of Ovid's own culture, have been amazingly good at mixing concrete and choosing stone that remains intact for two millennia or so. (Just think of the concrete-domed Pantheon, or my favorite unmortared aqueduct, in Segovia.)

But many building materials begin to break down long before that. For example, the Lake Superior Brownstone (LSB) here on the Durand Institute is suffering significant changes, at least in some places, after doing its duty for thirteen decades. It still looks just fine from a little distance, but if you know where to look, you'll spot interesting physical and chemical transformations taking place.

In this spot, there is both comb-chiseled and rock-faced ashlar. The former seems to have collected a denser coating of soot, though a lesser amount of grime is also evident on the cross-bedded blocks beneath it. And on one side it's home to quite a colony of foliose lichens as well.

The best way to see how much darker this feldspathic sandstone has become is to hunt for the patches where the old surface has spalled off to reveal lighter and still unweathered rock.

The spalling itself is the result of the weathering process known as case hardening. Water-soluble minerals originally distributed through the LSB are drawn out to the surface, where they accumulate and form a hard outer crust. The interior, however, is now bereft of these binding agents and so is softer and more crumbly. And eventually the outer rind breaks off to reveal the more vulnerable material.

Even the metal handrail is showing its age. It seems to have a bluish-green tinting suggestive of carbonate or sulfate weathering compounds of copper, but in addition it has corrosion spots more characteristic of iron oxidation. Hmm. Add to that the red stuff on top of it that looks like residue from the spalling stone above it.

Finally, much of the beaded mortar separating the comb-chiseled ledge from the blocks beneath it has fallen away. It looks like it's time for a little repointing.

To see the other photos and descriptions of this series, visit
The Brownstone Chronicles album.

Taken in: United States / Illinois / Shields Township / Lake Forest (show map)

Taken on: March 11, 2019

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Camera: NIKON COOLPIX A10, f/3.2, 1/100 sec, 4.6mm, ISO 80 (more info) (hide info)

Camera:	NIKON COOLPIX A10
Aperture:	f/3.2
Exposure Time:	0.01 sec (1/100)
Focal Length:	4.6mm
ISO:	80
Exposure Bias:	0 EV
Flash:	Off, Did not fire
Exposure Program:	Program AE
Metering Mode:	Multi-segment
White Balance:	Auto
Color Space:	Uncalibrated
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