Stories in Stone

by David B. Williams

  Over the past few years, a cured pig fat called lardo di Colonnata has achieved a certain status among epicures, but for Carrara’s cavatori, lardo has been a staple of their diet for centuries—a cheap, abundant food that tasted cool and refreshing on a hot day. I knew I couldn’t quarry stone, but at least I could eat like a quarryman. The Carrarese make lardo in their dank basements by curing raw pig fat in a tub of marble. Additional flavor comes from a combination of rock salt, pepper, garlic, and rosemary. Like the cavatori, I ate my thin slice of lardo with onion and tomato on bread. It had a creamy, translucent texture and melted deliciously in my mouth. I followed it with a shot of espresso. Geologizing doesn’t get any better than this.

  Energized by pig fat and caffeine, we headed back out to find rocks. Conti whisked us down the road to a spectacular view into the Torano basin, where I could finally get a sense of the scale of quarrying. In the center of the valley, fifteen hundred feet lower and three quarters of a mile away, a ledgy quarry, known as Polvaccio, stairstepped up the valley face. Polvaccio has been worked since Roman times and was where Michelangelo quarried his Pietá block. Through my binoculars, I counted eighteen ledges of marble, each of which, Conti explained, was between fifteen and thirty feet thick.

  Road after road zigzagged up the nearly vertical faces, faces covered white in marble by decades of quarry debris. The bends on the quarry roads are so sharp that trucks cannot turn and instead back down every other switchback. More roads climbed the valley wall below, as well as the smaller valleys south and east of Polvaccio. At the high points of the southern and eastern valley ridgelines, quarries had lopped off the summits, creating openings shaped like gun sights. “I remember when there was a mountain there,” said Conti. The view was one of the most spectacular and disturbing I have ever seen.

  “A thousand trucks a day carry stone out of the mountains,” he said, as he discussed how quarrying has changed in the past few decades. Most do not transport blocks of marble. More stone now leaves Carrara as basketball-sized hunks to be used as a powdered, industrial filler called ground calcium carbonate (GCC). You probably have used a GCC-enhanced product. GCC makes paper whiter and more opaque. It stiffens plastic, in products such as garden furniture and coffeemakers. Ground-up Carrara marble goes into paint to prevent corrosion. GCC is also a filler in toothpaste, so brush up—if Carrara was good enough for Michelangelo, it’s good enough for your teeth.

  As GCC quarrying has expanded in the past twenty years, it has come at a cost. GCC is made by blasting the marble mountains, collecting the smithereens, and crushing, grinding, and sorting. Although GCC produces less waste, or ravaneti, than quarrying for building or sculpting purposes, it generates a finer waste, the snowlike slopes of the Torano basin.

  Ravaneti in the good old days consisted of fist-sized stones, impure or partially worked blocks, and perhaps a broken column or capital. Water from rainstorms could percolate down through the spaces in the loosely packed material. GCC ravaneti, in contrast, originates from finer-grained material that doesn’t get caught in sieves. It forms impermeable layers within the older ravaneti. Water that formerly could soak into the ground now builds up on the steep slopes and what would have been insignificant rainstorms now weaken the ravaneti and trigger landslides. In 1996 and 1997 researchers recorded fifty-two slope failures, the largest of which slid over two thousand feet.32

  GCC production has added another danger. Those thousand trucks have only a few roads to use through town and one goes by a school, which led a group of mothers to stage a protest by throwing garbage in the road and stopping the trucks. Conti explained that although the town owns the quarries, which are leased to quarry operators, marble so thoroughly dominates Carrara’s economy that passing any regulations, either safety or environmentally oriented, faces stiff challenges.

  Our final stop was in the Colonnata valley, at a small quarry where an earlier owner had placed a slab of marble carved with a quote from Dante’s Inferno. Many Carrarese take pride that Dante spent time in the area in the 1300s and mentioned the marble in his epic poem.

  Conti had stopped not to admire Dante’s verses but to look at the quarry and the blocks perched on the ledges above it. One of Michelangelo’s assistants described the color of Carrara marble as being like the “moon reflected in a well.” A lyric image, but Conti’s and others’ detailed studies show that Michelangelo’s pure white variety, known as Marmo statuario, is rare. More often traces of carbon or pyrite shade the Carrara gray. The rock’s location within the folds affects the mixture and texture of the impurities. Conti pointed out the most common types, blends of gray and white, called Marmo ordinario and Marmo veneto, as well as blocks of the rarer, pure gray Marmo nuvolato. Nearby were several blocks of the striped Marmo zebrino, which on one block had been tightly folded into a narrow V. Another block recalled a frozen sea breaking to pieces and is known as Marmo arabesque.33

  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

  READING,WRITING, AND

  ROOFING—EAST COAST SLATE

  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 t
he 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.