Harley Earl, legendary vehicle stylist for General Motors from 1927 through the end of the 1950s, revolutionised the design of mass-produced automobiles by thinking of the car as a work of art — or, at least, fashion — rather than a purely utilitarian product. One of his main weapons in that revolution was clay. A sculpted model helped his clients (first, movie stars and millionaires, and later GM executives) get a feel for a proposed design in a way that sketches and diagrams simply couldn’t communicate.

But that was a long time ago, and modern automotive designers now have at their disposal computers, specialised design software, giant monitors, large-scale 3D printing, computerised milling processes, and fancy virtual reality setups. Yet, the automotive design gods continue to take handsful of clay, and breathe into them the breath of life.

“Why clay?” laughs Joe Dehner, Head of Ram Truck and Mopar Design for Fiat Chrysler, “I asked the same question when I got here 28 years ago, yet here we are doing the same thing. I explain it as using an erasable pencil versus permanent ink, and clay lets you go back and make changes.”

Lloyd VandenBrink, modelling manager at Ford Truck Studio in Dearborn, Michigan, is a big believer, as well. “Clay has two characteristics that make it good for use. It’s easy to change — you just add it, or take it away. It allows you to be creative and come up with something quickly. 3D printing, on the other hand, is just that — printing.”

“Secondly, it’s a great collaborative tool,” he continues. “Everyone can get around it, brainstorming three-dimensionally.”

The first thing to know about this marvelous medium is that it isn’t actually clay. “Clay is different waxes with some filler in it,” says VandenBrink. “That used to be sulfur, and more recently small glass beads, but it’s mostly waxes. Honestly, it’s hard to know exactly what’s in it, because the formulas are proprietary.” There are half a dozen companies that make plasticine clay suitable for full-scale design modelling (a few car companies make their own blends), and they deliver their product to design shops on flatbed trucks by the pallet-load. In a typical year, Ford goes through about 100 tons of the stuff, formed into hard, extruded cylinders about 3 inches in diameter. When a designer is ready to build, a lump of it is heated to about 66°C (150°F), and applied.

I explain it as using an erasable pencil versus permanent ink, and clay lets you go back and make changes.

This isn’t a reductive process, in which a sculptor just removes everything that doesn’t look like an SUV (that’s the role of a milling machine, more of which later). Instead, hand modeler applies the clay to 12 to 18 inches of foam cut into the rough shape of a vehicle, which is itself attached to an armature of lightweight aluminium with adjustable fittings. Those fittings are placed to reflect the briefing the designers are working from, so that the model is built with hard constraints showing overall wheelbase, powertrain, and people packaging. “The model would weigh probably ten tons if it were all made of clay,” notes Dehner.

The entire design process takes about a year, starting with concept sketches and working to delivery of what Dodge’s Dehner calls a “toolable surface for the engineering team.”

Between paper and pavement, design follows a path that’s linear, but with a lot of loops as changes are integrated, tests are run, and outside opinions are brought in. First there are concept sketches and designs, and a few of those are made into scale models at 4:10 scale. Usually, those models are made directly from a CAD program running a milling machine, in which a block of clay is whittled down to form a meatspace model of what’s been living inside the computer. From there, a few are selected and distributed to interested parties (management and marketing in particular) before a base design is selected for full-scale modelling.

That leap to full-size is vital. “There’s something about having that scale on a physical model,” says VandenBrink. “We do scale models, and make them as realistic as possible, but when we scan and blow it up full size, it looks cartoony.” There’s a flip side as well, he says. “When you work on a computer, you have a tendency to zoom in, and you get too concerned with the details. You end up spending hours working on the radius of curve, when it’s just going to get lost in the stamping.”

One thing that’s often overlooked about clay models is that they aren’t simply output; clay can be an input medium, as well. The perfect fender curve or B-pillar transition may take shape with a few flicks of the wrist in clay, while trying to get that same level of artistry through computer and stylus might take hours. And once it’s in clay, a whole car can be scanned into a CAD program in an hour and a half. You won’t do that with a stylus, or a mouse, or a fancy 3D headset.

Testing is another place where the flexibility of clay is key. “Wind tunnel time is expensive, but you need to confirm your design to get the most efficient exterior,” says Dehner. “It’s easy to slap on a little more clay and make a shape, so you get more runs and get more data.”

I keep hearing, ‘virtual reality is coming in, and is going to take away the whole thing.’ But we need to understand that it’s not an either-or, it’s a hybrid of all the different tools we need to get where we need to go.

As a design reaches maturity, items like headlights and turn signals get added to clay to turn it into a “hard model.” The entire model is then coated with a stretchable modelling film (known, Kleenex-like, by the original trade name DI-NOC) that mimics the look and feel of a painted surface. (“From 10 feet away you’d never know it wasn’t a functioning car,” says VandenBrink.) The design remains flexible, though, with clay being smoothed on or scraped off until the final design is approved by corporate executives milling around in some secret interior courtyard. Once that happens, a model (still nonfunctional, but very expensive) of fiberglass or resin, perfect inside and out, is created for people to see at press events and car shows.

And that clay model? At Dehner’s design studio, the full-size models are whisked off to a secret storage facility called The Tomb. “Once we’re sure that the program has truly moved on, then we’ll take it apart and recycle.”

At Ford’s studio in Dearborn, there are about 160 modellers, 125 of whom can model by hand, with many being able to drop what they’re doing in a CAD program to scrape clay from a fender. Some come from design schools with specialisation in auto design, but others come from the auto-body industry, or from the arts. But not a lot of future designers think about clay on their career path, according to VandenBrink, so Ford sends recruiters to colleges and offers training internships. “We have to spread the word that this exists,” he says.

Part of that lack of awareness may be that clay modelling seems so old-fashioned. VandenBrink says, “I keep hearing, ‘virtual reality is coming in, and is going to take away the whole thing.’ But we need to understand that it’s not an either-or, it’s a hybrid of all the different tools we need to get where we need to go. In the 80s we invested in milling, and everyone thought it was the end of clay.” But here we are, still scraping.

“Up to this point,” says Dehner, “we’ve simply never found anything better.”

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