When stop-motion animation meets visual effects, the creative process can be both demanding and rewarding. For the short film The Girl Who Cried Pearls, the production team faced a unique challenge: enabling the puppets to speak without altering their intricate designs. This led to a technical journey filled with experimentation, ultimately resulting in an innovative solution using invisible ink and ultraviolet (UV) light.

Eric Pouliot, Technical Director of Animation at the National Film Board of Canada (NFB), shared insights into the process. Assigned to the project in 2019 as his first role with the NFB’s French Animation Unit, Pouliot was tasked with finding a way to animate the puppets’ mouths for CG replacements. While his initial approach leaned toward digital solutions, directors Chris Lavis and Maciek Szczerbowski encouraged a spirit of exploration and innovation.

For nearly twenty years, Chris and Maciek have collaborated with the NFB to push the boundaries of visual effects in animation. With The Girl Who Cried Pearls, the team needed a method that was both functional and inventive. Many VFX supervisors suggested traditional techniques such as modifying the puppets’ features or adding visible tracking markers. However, the directors were committed to preserving the puppets’ original appearance, ruling out any physical alterations or visible markers.

The breakthrough came when Pouliot was inspired by a neon black-light dance performance, which used glowing patterns visible only under UV light. This sparked the idea to use invisible tracking points that could be revealed with UV exposure. Since stop-motion animation captures each frame individually, the team could shoot every frame twice: once under standard lighting for the final image, and again under UV light to reveal the tracking points. This process was facilitated by DragonFrame’s multi-exposure and automated lighting features.

The next step was identifying a suitable paint that would remain invisible under normal lighting but glow under UV. The puppets, made of latex and finished with delicate paintwork, required a solution that wouldn’t damage their surfaces or become visible in the final footage. After testing various highlighters and glow-in-the-dark paints, Pouliot discovered the OPTICZ Invisible Ink Pen, commonly used in security applications. This UV-reactive, water-resistant ink adhered well to the latex and remained invisible under regular lighting, while providing reliable tracking points under UV.

This approach allowed for precise and consistent tracking without compromising the puppets’ appearance. The UV-reactive ink not only solved the immediate technical challenge but also preserved the artistic integrity of the puppets. Remarkably, the invisible markings have endured, and the puppets still glow under UV light six years later.

The use of invisible ink and UV light in The Girl Who Cried Pearls stands as a testament to creative problem-solving in animation. By thinking beyond conventional methods, the team achieved a seamless integration of VFX and stop-motion, opening new possibilities for future projects.

• Project: The Girl Who Cried Pearls
• Directors: Chris Lavis and Maciek Szczerbowski
• Technical Director: Eric Pouliot
• Studio: National Film Board of Canada
• Year of R&D: 2019

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