Stories in Stone (31 page)

Tectonic stresses also affected the internal crystalline structure.
More deeply buried marble developed larger crystals of
calcite with straight grain boundaries.
This is the rock Michelangelo wanted because it is easy to work and allows light to
penetrate deeply.
In contrast, crystals in the heart of a fold developed an elongate fabric, like a grain of rice, a texture
that resists weathering and bending but is hard to sculpt.
Another rock difficult to sculpt but good for building panels resulted
from Carrara getting slightly rebaked during its long-term burial and having its straight-edged grains changed to serrate-edged
ones.
These various textures can be found throughout the Carrara quarry district, with single quarries containing all three
textures.

A detailed understanding of the internal structure has helped clarify one of the long-known curiosities of Carrara, the exploding
block of marble.
According to an American geologist I know, truck drivers would stop in a bar on the way out of Carrara and
come back out to their rigs to find blocks that “just popped and exploded.” Nothing so dramatic happened, said Conti, but
the edges of blocks would start to fall apart because of the release of stress on strained, or deformed crystals.
In essence
the stone was stretching after being released from its millions of years of squeezing.
Conti added that quarry workers have
an easy method for dealing with potentially exploding stone.
They sweep their work area clean each night; if they find debris
on the ground in the morning, they know their quarry walls may not be safe.

John Logan, the geologist hired by Amoco to determine what went wrong with their Carrara panels, also has studied the Carrara’s
internal structure and geologic history.
He placed much of the blame for panel warping on the stone’s past.
³⁴
First, that warm, shallow sea of 200 million years ago produced calcite that was the basis for marble formation.
Calcite
has an unusual characteristic that emerges when the sun bakes marble on a regular basis.
Thermal radiation starts to expand
calcite crystals along one of their three internal axes, or dimensions.
Heat-induced expansion is an attribute that all of
us have experienced: Just think of a balloon sitting in a hot car.

Calcite also contracts along different internal axes when heated.
Known as anisotropy, the change becomes a problem when calcite
cools because crystals that have grown and shrunk jab into each other and cannot return to their original shape.
Over time,
with “thermal cycling” and the “mismatch in expansion and contraction,” as Logan has written of the changes, the disturbed
crystals can alter the shape of a panel.

Carrara’s metamorphic history created the second problem for the Amoco panels, said Logan.
Once anistrophic calcite growth
weakened the marble, it became more susceptible to a release of stress, also seen with the “exploding” blocks of marble.
Although
some sections of the marble deposits experienced more folding than others, all marble in Carrara suffered during metamorphism,
so all marble will release strain at some point in time.
When that marble is a thin slab and it’s tightly secured in place,
it can warp and bow to the point of failure.

Near the Dante quote, Conti also pointed to several rusty pulleys mounted into the wall.
They were left over from cutting
technology developed in the late 1800s called the helicoidal wire saw, sort of an industrial-scale Rube Goldberg contraption.
It worked like a modern diamond wire saw cutting down through the marble like a wire cheese slicer.
But this cheese slicer
was more akin to one that sliced cheese with a wire moving along at fifteen feet per second that started in the kitchen, traveled
down a hallway, around a corner, and up a flight of stairs to the den, where the block of cheddar was placed.

The helicoidal wire consisted of three strands of steel braided into a quarter-inch-thick wire.
Speeding along, the wire traveled
away from a motorized drive unit, over wheels mounted on a guidepost or wall, to a movable rig consisting of four pulleys.
By passing through the pulleys and turning ninety degrees at each, the wire formed a rectangle.
Cavatori
cut a block by lowering the four pulleys until the wire bottom of the rectangle slid across and abraded the marble.
A slurry
of sand and water facilitated the cutting.
Helicoidal wires could be over a mile long to allow the steel strands to lose their
heat.
The wires dramatically improved quarrying techniques, but if a wire snapped, whipping across the quarry, the results
could be calamitous and deadly.

Transport also improved in the nineteenth and twentieth centuries from what Michelangelo had to deal with.
Trains arrived
in 1876 to ferry stone to the sea, but not until the 1910s did tractors, called
ciabattoni
, or shufflers, replace the oxen-drawn carts used closer to the mountains.
Another decade would pass before winch-pulled trucks
resting on rails took over the human-powered
lizzatura
slopes.
Instead of dying under the wheels of carts or getting crushed by blocks crashing down a
lizzatura
, the
cavatori
had the pleasure of breathing the dirty air produced by inefficient machinery.

None of these earlier advances showed up on Conti’s quarry tour.
All that remained were a few rusting pulleys and an abandoned
lizzatura
or two.
Diamond wire saws, hydraulic hammers, trucks, and front-end loaders were the new tools of choice, just as they had
been in Indiana and Minnesota.
With the machines, the
cavatori
have cut deeply into the mountains in the past fifty years and have removed more stone than in the previous two thousand.

Active quarry, Colonatta basin, Carrara, Italy.

As we left Colonnata and rejoined the main quarrying road back to Carrara, truck after truck rumbled out of the quarries.
The majority were filled with blocks destined to be crushed and ground to powder.
Only a few carried the big blocks needed
for architecture or sculpting.
Michelangelo’s marble has now become more valuable as an industrial powder than as a sign of
elegance and opulence.
The fate of the Amoco marble, as a pond filler, is being replayed on a global scale.

“Everyone will tell you that Michelangelo’s stone is the worst for building,” said John Logan.
“The rock is too porous.” Michelangelo’s
Marmo statuario
has a coarse-grained texture with smooth boundaries between grains, which allows water to seep into the marble and weaken
it.
Perhaps a greater irony than using Michelangelo’s marble for toothpaste is that Michelangelo, who sealed Carrara’s reputation
for beauty and prestige, chose a variety of Carrara with such poor qualities for architecture.

Amoco’s troubles exemplify how the prestige and allure of marble can lead architects and builders down a slippery trail, but
Edward Durell Stone and John Swearingen were not alone.
An international study in 2005 found marble panel warpage from Cuba
to Australia, with a concentration in Scandinavia.
Finlandia Hall in Helsinki, designed by the great architect Alvar Aalto,
had its Carrara marble panels replaced in 1999 because the marble bowed concavely, as opposed to Amoco’s, which bowed convexly.
Finnish designers chose Carrara again.
The new Carrara panels began to bow within a year, but this time they bowed convexly.
Three towers in Lidingo, Sweden, are more peculiar; the marble panels bow convexly and concavely on alternate rows.

Like Stone and Michelangelo, the architects of these buildings had been seduced by marble.
Each designer knew that when they
used marble, people would read the stone and see it as shorthand for grandeur.
They didn’t have to boast or shout about their
clients; the marble would speak for them.

“The trend of corporations [is] to recognize the value of good architecture and its influence on the morale and pride of its
personnel and the prestige that architecture can give to a business enterprise .
.
.
Apparently the belief that ‘Good architecture
is good business’ is gaining ground,” wrote Edward Durell Stone in his memoir,
The Evolution of an Architect
.
³⁵
I wonder how the failure of the Carrara marble, particularly in a company that employed hundreds, if not thousands, of geologists,
affected those employees.
³⁶

Perhaps good architecture might benefit from some good geology.
Another Stone-designed, Carrara marble–clad skyscraper opened
in Toronto in 1975.
The panels of First Canadian Place have also bowed extensively, and on May 12, 2007, a 250-pound panel
dropped fifty-two stories and crashed onto a roof below.
First Canadian’s owners haven’t ruled out recladding the building.

9

R
EADING
,W
RITING
,
AND
R
OOFING
—E
AST
C
OAST
S
LATE

He was like a general on a battlefield of slate.

—Johnny Cash, “The Baron”

Here was a demonstration that a slate could speak in a foreign tongue.

—Hiram Bingham,
A Residence of Twenty-one Years in the

Sandwich Islands
, 1847

I
ATTENDED AN elementary school three blocks from where I lived.
Built in 1906, it was an elegant three-floor structure made
of wood on a foundation of brick.
A portico with fluted Ionic columns framed the front entryway, although I generally entered
through the plain back door because it was closer to home.
Above the front doors, which repeat the pediment-column pattern
of the portico, in black script, was written ISAAC I STEVENS SCHOOL.
As every child who passed beneath those words learned,
Stevens was Washington State’s first territorial governor.

Wide stairways with banisters, perfect for sliding down, connected Stevens’s three floors.
The hallways had wood floors and
dark wood paneling and were not well lit.
In contrast, the thirteen-foot-high classrooms had windows that stretched almost
to the ceilings.
If you were lucky, you got to pull down the long window shades when the teacher hauled out the movie projector
for some grainy black-and-white instructional film.
At the back of each classroom was a small room where we hung our coats
and stored our lunches.

But the focus of class was the slate blackboard at the front of each classroom.
I am sure that one of the things each of my
teachers did on the first day of school was to write her name on the blackboard in large, blocky letters.
Miss Smith.
Mrs.
Bangs.
Miss Baker.
She wrote on a glistening blackboard, recently washed and ready for a new year of students.
Along the bottom
ran a wooden tray, which held erasers and fresh sticks of chalk.
As the weeks of school progressed, the board turned gray,
the chalk eroded and broke, and the tray became covered in chalk dust, but a quick wipe with a wet cloth could return the
board to a pristine state and no matter how well worn the chalk was our teacher could always find some bit to write with.

Over the years, I probably went up to the blackboard tens or hundreds of times.
That was where I struggled with spelling and
where I discovered how to add, subtract,multiply, and divide.
I am sure I got chalk dust on my clothes and in my hair.
I am
sure I occasionally wrote at the wrong angle and made the chalk screech as I went along.
I know I wouldn’t have done that,
or run my fingernails down the slate board, on purpose, because I still cannot stand those agonizing squeals.
I also remember
that like Bart Simpson, I invariably had to write “I will not .
.
.” over and over again on a blackboard, a penance for some
transgression or other.

When I wasn’t bad, I got to go outside and clean the erasers by clapping them together or hitting them against the brick foundation.
I remember that cleaning the erasers was a reward: I got to go outside, whack things, create clouds of dust, and do something
to please the teacher.
Other friends of mine, as well as my mom, remember eraser cleaning as punishment.
I also thought wiping
down the blackboard was fun.
The surface dried from shiny black to flat black almost instantaneously, as if the slate abhorred
being wet.

Friends from coast to coast told me similar stories of learning from blackboards, cringing at the chalk squeal, and cleaning
erasers.
Their association with blackboards continued through high school and into college.
Stories abounded of legendary
professors who would zing sleeping students with bits of chalk or equally infamous teachers who always had lines of chalk
stains on their backs.
Blackboards were as much a part of growing up as skinned knees, learning to drive a car, or dating.

Slate blackboards are a wonderful teaching tool.
They don’t break or warp.
They can be cleaned forever, either with an eraser
or with your hand.
They produce a pleasing click-clack sound when written on properly.
Often taking up an entire side of a
room, they provide a blank wall for jotting down anything from music to drawings to numbers.
They also seem eternal and permanent.
Just think of the photographs of Einstein, or any number of mathematicians and physicists, writing out complicated equations
on a blackboard and you will recognize the role they have played in education and communication.

Or consider how our use of slate blackboards has seeded our language.
We wipe the slate clean.
We chalk up something to experience.
We refer to a tabula rasa, literally a scraped tablet, but more often defined as a clean slate.
We vote for one of a slate
of candidates.
We are slated to do something and those who had a debt were formerly said to be on the slate.
No other stone
has contributed a comparable literary etymology.

The precursor to the blackboard was the school slate, a handheld tablet upon which students could write with chalk or slate
pencils.
¹
Made of slate with a wooden frame, school slates had been used for hundreds of years in Europe and were starting to become
more widespread in America in the late 1700s and early 1800s.

Blackboards arrived in America with George Baron, a military academy teacher from England.
According to historian Stephen
Ambrose, Baron began teaching math to cadets at West Point on September 21, 1801, and “illustrated his lecture by making marks
upon a standing slate with a white chalk, thereby introducing the blackboard to America.”
²
By the 1820s blackboards had spread to primary schools and colleges in Maine, Connecticut, and Massachusetts.

Not everyone cottoned to the newfangled blackboard.
In 1830, during a math class, the fine youth of Yale College rebelled
against having to describe a theorem depicted on a blackboard instead of using the traditional method of merely reciting from
a book.
The “Conic Sections Rebellion” resulted in the expulsion of forty-three of the ninety-six members of the class of
1832.
Not content with simply expelling the mathematic malcontents, Yale administrators sent the students’ names to surrounding
colleges alerting them to admit the reprobates at their own risk.

Teachers liked school slates because students could share and reuse them and teachers could bring them to exotic places.
Some
of the largest artifacts found at the Donner party’s final camp in the Sierra Nevada are pieces of slate, thought by archaeologists
to be school supplies carried across the country by Tamzene Donner.
In 1820 missionary Hiram Bingham helped introduce writing
to the Hawaiian islands with school slates.
³

Not all early blackboards were made from slate.
Many were simply wood boards painted with black paint, later modified to a
specially formulated application called liquid slating.
Toward the end of the 1800s, a wood pulp and cement mixture known
as hypoplate appeared.
These blackboards suffered either from cracking; chipping; warping; absorption of oil, dirt, and water;
or uneven wear, but they were inexpensive, at least in the short run.
For the long run, however, nothing could match slate.

Blackboard slate and the smaller school slates came primarily from Lehigh and Northampton counties in Pennsylvania.
Smooth,
durable, and uniform, the slate took chalk easily and legibly, didn’t absorb water, and stayed straight and true.
By 1905
the majority of blackboards sold in the United States were made of slate.
Six years later, the
Cyclopedia of
Education
reported on blackboards that “It is doubtless no exaggeration to say that [slate blackboards] .
.
.
should be used [in] all
brick, stone, or concrete buildings.”
⁴

Although I did not know it during my youthful days of scribbling on the blackboards at Stevens School, I could not have used
a better combination of materials for writing, at least from a geologic point of view.
If I could have looked at chalk dust
under a high-powered microscope, I would have seen a skeletal menagerie of countless single-celled marine algae.
Known as
coccoliths, they lived by the billions in the upper surface of the sea and were less than twenty micrometers wide.
Some had
shells shaped like steering wheels, others like pig-snouts surrounded by ruffles, and many resembled a hollow disc with radiating
fingers.
When these plankton died they accumulated in a white ooze on the seafloor and later lithified into chalk.

Pennsylvania’s slate also began as a muddy ooze deposited in an ocean, when rivers carried clay, silt, and sand out into a
deep marine basin.
The 450-million-year-old sediments first formed into shale, followed tens of millions of year later by
metamorphosis to slate, under thousands of feet of rock.
At present, up to seven thousand feet of slate beds make up the valleys
and ridges around Pen Argyl, seventy-five miles north of Philadelphia.
⁵

Chalk and slate are the peanut butter and jelly of the geology world.
You can write on many surfaces with chalk, and other
stones can write on slate, but no combination looks as good or works as well together as slate and chalk.
It is a relationship
that needs no special preparation or processing.
Any chunk of chalk writes perfectly well on any slab of slate.
No other pair
of rocks has such an integral and elemental connection.

Slate has dozens of uses aside from blackboards, though none of the uses are grand or known for their exquisite beauty or
elegance.
Instead, slate became the most utilitarian of materials, the building stone you turned to because “it is non-absorbent
and germ-proof .
.
.
sanitary and easily cleaned,” as one early promoter described it.
Slate doesn’t compress under a load
so it works well as paving, floor tile, and steps.
It also can be inscribed in great detail and resists erosion, making it
ideal for grave markers.
Hard and impermeable, it works well for desktops,wainscoting, and urinals.

We look to marble for its beauty.
We turn to granite for its durability.
We build with brownstone because the Vanderbilts
did.
Sometimes, though, we just need a rock that gets the job done.
Nothing fancy or famous or beautiful.
And for that, no
rock surpasses slate.

If you had been born a hundred years ago, you would have rarely spent a day of your life without seeing slate.
Your mother
would have washed your clothes in a slate laundry tub, set you to rock in a cradle next to a slatemanteled fireplace, and
chopped food on her slate countertop.
Your father would have used slate if he worked at a leather factory, brewery, or printing
shop.
When friends visited, they could have tied their horse to a slate hitching post, stepped over a slate curb, walked over
a slate sidewalk, and up slate steps to enter your slate-floored residence.
As electricity in the home became widespread in
the 1920s, your family would have purchased slate electrical panels, because they could be drilled cleanly, didn’t warp, resisted
fire, and didn’t conduct electricity.

The years around the turn of the twentieth century were the halcyon days of slate, when it was the modern equivalent of plastic:
ubiquitous and practical.
You’d be less likely to encounter slate today, in a modern home.
Slate floors and countertops have
had a resurgence of popularity, but few people seem to want to go back to the slate laundry tub or slate refrigerator shelf.

Of all slate’s many applications, roofing is by far the stone’s most widespread use.
In 1830 an estimated 50 percent of the
homes in New York City and one-third of the homes in Baltimore had slate roofs.
During the peak years of slate production
in the early 1900s, 75 percent of all quarried slate went to roofing.
⁶

No other natural roofing materials possess qualities as appropriate for roofing as slate.
Fireproof, resistant to rain and
snow, and able to withstand high winds, a slate roof doesn’t rot or get eaten by insects.
Slate shingles don’t deteriorate
in the sun.
They don’t curl and lose their water resistance with age.
They also look good and can last for centuries.

Some of the earliest archaeological evidence for slate roofs comes from Roman-era England.
The eighteen-by-twelve-inch shingles
resemble the bottom end of a necktie, with a flat top and triangular bottom.
A single iron nail held the slate in place.
Although
archaeologists suspect that the use of slate roofing faded when the Romans left, by the 1300s slate roofing was on the rebound.