Molding & Casting Bruce's Dorsal Fin from JAWS (1975)
In November 1973, two unsung heroes of movie magic — production designer Joe Alves and mechanical effects wizard Robert Mattey — were tasked with bringing terror to life. Their assignment? Build not one, but three mechanical sharks for Steven Spielberg's new thriller, Jaws. The most famous of them, lovingly nicknamed Bruce by Spielberg, was notoriously difficult to work with on set. But despite the mechanical headaches, Jaws became a cultural phenomenon and box office juggernaut, with Bruce becoming a true icon of modern cinema.
By 1976, Universal Studios capitalized on the film’s success by repurposing screen-used props into a Jaws attraction for their Hollywood backlot tour. Among these cinematic relics was a massive dorsal fin, prominently featured during the ride's heyday.
Fast forward to 1986, when a young visitor to Universal Studios encountered that very shark fin. At the time, he had no idea he was standing next to a genuine piece of film history. Two decades later, he discovered the truth — the fin was from the original Bruce. While the full shark animatronic had been sent off to a junkyard, its dorsal fin survived, though barely.
Luckily, Hollywood effects artist Greg Nicotero and KNB Effects took on the task of restoring Bruce, who now proudly hangs from the ceiling of the Academy Museum of Motion Pictures in Los Angeles. But this story doesn’t end there — the same passion for preserving movie history inspired one fan to recreate Bruce’s dorsal fin using modern mold-making techniques.
From Fin to Form: Rebuilding an Icon
Reproducing the shark fin was no small feat. The first step? Scanning the original fin to preserve its dimensions, just in case something went wrong during molding. Using cardstock and plywood, the shape of the fin was traced, cut, and prepped for a two-part silicone mold. A wooden silhouette was attached to split the fin in half, which allowed for the first half of the mold to be made.
Oil-based clay was used to seal any gaps — avoiding sulfur-based clay, which reacts poorly with silicone. Then came the painstaking process of adding silicone, building up layers for strength and accuracy. Mold "keys" — small clay shapes — were embedded into the walls to ensure both halves of the mold aligned perfectly when assembled.
The artist also added trapezoidal silicone keys and layered on fiberglass and Cabosil-thickened resin to make a rigid outer shell, or mold jacket. To ensure the resin didn’t stick to the wood silhouette, everything was carefully waxed beforehand.
Casting the Fin
Once both mold halves were complete, they were bolted together, and a new fin casting began. The inside of the mold was painted with epoxy gel coat — the same durable material used in boats and motorcycle helmets — followed by several layers of fiberglass cloth. A precise edge application ensured the mold halves could be joined without overlap issues.
When the time came to remove the fin, a little elbow grease and patience paid off — the mold popped clean, revealing a near-perfect recreation.
Finishing Touches
To finish the piece, the artist trimmed excess material, applied Bondo to fix small imperfections, and carefully sanded the surface. Special care was taken not to damage the sharkskin texture inherited from the original fin. A final buff with acetone helped smooth the finish without losing detail.
The result? A beautifully crafted tribute to one of cinema's most fearsome creatures.
Preserving Film History, One Mold at a Time
Whether you're a prop collector, a DIY mold-maker, or simply a Jaws superfan, this project is a testament to the passion and ingenuity that goes into preserving Hollywood history. From Universal Studios' backlot to a home workshop and finally to a fiberglass casting of Bruce’s famous fin, this journey reminds us that movie magic doesn't end when the credits roll.
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