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ENGINEERING

A Round Pie in a Square Box

Mismatched pairs of simple things can inspire ingenious solutions

Henry Petroski

Out of Shape

2011-07PetroskiFA.jpgClick to Enlarge ImageThe world of things is full of mismatched objects. Like round pegs in square holes, they do not fit neatly together. But when they are joined, neither do they easily fall apart. The world of things can be a world of awkward pairings, marked by misfit, imperfection and compromise, but even in these there can be lessons to be learned about why and how they came to be. And their stories can reveal the secrets of how so many things do fit together, albeit imperfectly.

The white-boxes-and-string world of the old-time bakeshop is alien to the baked-goods department of today’s supermarket. Here, most things are prepackaged in transparent plastic cases formed to conform to the shape of their contents. Round pies tempt us from beneath round transparent domes. Tops snap onto bottoms and lock in place without the use of string. The packages are neither biodegradable nor easily carried with one hand, but they do fit, if not geometrically congruently—along with the round cans and bottles and globular fruits and vegetables—into the ample trapezoidal hold of a shopping cart. The incongruity of things made and things found is a fact of life, and like most facts of life it is accepted as the way things are, if not embraced as welcome variety. Maybe it would be a more efficient use of resources and space if all things, including pegs and holes, were square, but who would want to slice a squarish pie or catch a cubic ball?

So, we not only accept the shapes of the world as we find them, but we also adapt to the idiosyncrasies of their interaction. And one of the most common surviving examples of this is the round pizza delivered in the squat square box. As my father accepted without comment his chocolate cake and apple pie in white boxes bound in candy-cane string, so most of us accept our pizzas in corrugated-cardboard containers that come in a wide but limited range of styles and colors. The basic container comes in the neutral earthen color of corrugated-cardboard boxes, but some restaurants think it to their advantage to use white cardboard and imprint the boxes they use with the name of the business, often in the green, white and red colors of the Italian flag. However dressed up, the corrugated-cardboard box is near-ideal packaging for a hot pizza that must endure a 15-or-so–minute journey from commercial oven to domestic table.

Relatively thin and unreinforced cardboard, the stuff of which cake and cereal boxes are made, is a rather flimsy material and hardly suitable for bearing the weight of a pizza pie distributed over the reach of a 16- or 18-inch circle. That box material worked for pies and cakes not only because their diameter is typically only about eight inches, but also because they were usually supported by a pie tin or cake base that enforced their burden’s flat shape. Pizza pies, on the other hand, are notoriously soft and floppy—especially when they are hot—and if there is anything between them and the box they are placed in, it tends to be a flimsy sheet of waxed paper, whose purpose is to provide not structural stiffness but a modicum of gentility. Where the pizza is especially oily, the paper also may help keep the box bottom dry.

Like the old bakery-cake container, every pizza box begins as a flat sheet, which is die cut into an irregular shape that can be folded into a (usually prismatic) box. Like the cake container, the box gains stiffness by being closed, but with the flaps tucked inside rather than being tied down outside. Some of us have experienced the transformation from flat to full first-hand by assembling gift boxes out of the unassembled parts we have been provided by a department store. For those of us who have not, we can reverse engineer any cardboard box to gain a tactile appreciation for the advantages of the closed structure. We know from shopping at the supermarket that full and sealed boxes of corn flakes hold their shape and protect their fragile contents through the successive processes of being filled at the plant, packed into cartons there, shipped to the store, stocked on the shelf, taken down from the shelf, placed in the cart, slid past the scanner, thrown in the bag, stuffed in the car, jostled on the road, dropped on the drive, squeezed into the pantry and brought to the table—intact. Soon as the box is opened, however, we can feel its rigidity drop. That is because the sealed top had prevented the sides from altering their geometry.

Reverse engineering the cereal box begins with emptying it of its contents and unsealing the bottom. This leaves an open-box structure, which is readily felt to be much less rigid than its closed counterpart. The doubly-opened box can be sighted through, as if it were a tube. However, unlike a circular tube, whose shape cannot be changed without some crushing, the rectangular tube of the cereal box can be transformed into a parallelogram without altering the flatness of any of its sides. It is this nature of the rectangle that requires it to be braced with diagonals if it is to be used as a basic structural shape for, say, a building or a bridge. Since diagonals bisect a quadrilateral shape into triangular ones, we see triangles dominating the structural pattern of so many bridges and buildings—at least before they are clad in an architectural facade. Without diagonals, the open cereal box is more a mechanism than a structure, and its interior shape can be transformed from rectangle to parallelogram and even to a flattened box with ease. Locating the seam that usually runs down one corner of the box and separating its glued surfaces allows us to open the box fully and lay its insides flat out. This is how the cake box in the bakery and the pie box in the pizzeria are delivered from the box factory.

The corrugated cardboard box is remarkably well-suited for transporting a hot pizza, and this is no doubt why for decades it has remained generally unchanged in design and use. Starting out flat as it does, it takes up relatively little storage space, which is often at a premium in mom-and-pop pizza shops. A basic pizza box is relatively inexpensive, costing perhaps 25 cents when bought off the Internet in lots of 50 and considerably less when purchased wholesale in chain-store quantities. Corrugated cardboard is a relatively stiff material and so, especially when closed, a box made of it is good at holding its shape and so at preserving the shape of its contents. In addition, the nature of the corrugation process is to include channels of air in the sandwich structure, thus providing insulating properties somewhat similar to those of a double-glazed window pane. This, of course, helps the pizza retain its heat while in transit. Finally, cardboard is absorbent, and so to a degree keeps olive oil or other pizza juices from dripping out.




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