What Is Cel Animation, And How Does It Work?

From Ink and Paint to Pixels and Code: The Enduring Principles of a Handcrafted Era

There’s a particular magic to the animated classics, the fluid warmth of Snow White, the expressive energy of The Lion King, the breathtaking depth of a Studio Ghibli landscape. This magic wasn’t conjured by algorithms but born from the meticulous, frame-by-frame alchemy of cel animation. For over half a century, this labor-intensive craft was the heartbeat of animation, requiring armies of artists to hand-draw and paint on transparent celluloid sheets

From Flipbooks to Feature Films

Cel animation, short for “celluloid animation”, was born out of necessity in the early 20th century. Before cels, animators drew every single background element on every frame,  a soul-crushing amount of redundant work. In 1914, Earl Hurd patented the cel technique: painting moving characters on transparent sheets of celluloid (later acetate) and layering them over a single painted background. Suddenly, studios could churn out cartoons faster, cheaper, and with jaw-dropping consistency.

By the 1930s, Walt Disney perfected multiplane cameras and xerography, pushing cel animation into full-color, cinematic territory. Snow White and the Seven Dwarfs (1937) became the first feature-length cel-animated film. For the next six decades, nearly every theatrical animated movie,  The Lion King, Akira, The Iron Giant,  relied on this labor-intensive yet breathtaking process until digital tools finally took over in the late 1990s and early 2000s.

The Step-by-Step Magic: How Cel Animation Actually Works

1. Storyboarding & Animatic

Everything starts with storyboards,  comic-book-style panels that map the film shot by shot. These are timed with temporary dialogue and sound effects to create an “animatic” (a moving storyboard). This is the blueprint no studio skips, whether they’re making a 90-minute feature or a 15-second brand loop.

2. Character Design & Model Sheets

Artists create hyper-detailed model sheets showing characters from every angle, complete with color callouts and expression guides. Consistency is everything when hundreds of animators will touch the same character.

3. Layout & Background Painting

Layout artists draw the scene composition in pencil, defining camera moves and perspective. Master background painters then create gorgeous, static gouache or acrylic paintings,  often museum-quality works you only see for a few seconds on screen.

4. The X-Sheet (Exposure Sheet)

Think of this as the conductor’s score. The director and lead animator fill out a frame-by-frame chart telling the camera operator exactly which cel goes where, how many frames each drawing is held, and when dialogue hits. It’s the DNA of timing in traditional animation.

5. Key Animation

Senior animators draw the “key” poses,  the extreme moments that define the motion (the squash before a jump, the stretch at the peak). These are rough pencil drawings on paper, often tested in a “pencil test” video to check timing.

6. Inbetweening

Junior animators (or “inbetweeners”) create the drawings that smooth the motion between keys. For full animation, that’s usually on “ones” (new drawing every single frame) or “twos” (one drawing held for two frames). The more frames, the silkier the motion.

7. Clean-Up

Clean-up artists trace the rough animation with precise, consistent line work,  usually in pencil again ,  so every character stays perfectly on-model.

8. Ink & Paint (The Classic Cel Process)

Here’s where the “cel” part actually happens.

• Tracing: Inkers hand-trace each cleaned-up drawing onto a transparent acetate cel using crow-quill pens or, later, xerography (a photocopy-like process Disney pioneered for 101 Dalmatians).
• Painting: Painters flip the cel over and apply vinyl-based paints to the reverse side. Painting on the back prevents brush strokes from showing and creates that iconic crisp, saturated look. Each color had an official Pantone-style code; one tiny deviation and Cruella’s coat would look wrong for 1/24th of a second.

9. Compositing Under the Camera

A massive rostrum camera (think a refrigerator-sized precision machine) points downward at a pegged animation table. Background painting goes on the bottom. Then, in order, the cels: distant characters first, closer characters on top. The camera operator follows the X-sheet, shooting one frame at a time,  sometimes moving cels a fraction of a millimeter between exposures for parallax effects on multiplane setups.

10. Film Processing & Editing

Exposed film is developed, then physically cut and spliced in the editing room. Only when the workprint is approved does the final negative get conformed. That’s 10-15 months of work and thousands of painted cels for a single 80-minute movie. The Little Mermaid used over 1 million individual drawings and cels.

Why Cel Animation Still Turns Heads in a Digital World

Even though software like Toon Boom Harmony and TVPaint can perfectly mimic the cel look in a fraction of the time, there’s something irreplaceable about real paint on acetate under camera glass. The slight imperfections, the rich color vibration, the warmth of hand-painted shadows ,  digital tools chase it, but physical cels nail it.

Directors like Hayao Miyazaki (Spirited Away) and Richard Linklater (Waking Life, rotoscoped but still cel-painted) kept the technique alive into the 21st century. Modern indie studios like Cartoon Saloon (Wolfwalkers) and Science SARU blend hand-painted textures with digital pipelines to get “that cel look” without the insane overhead.

And yes,  even sleek Android app development teams study cel principles. The 12 Principles of Animation (squash & stretch, anticipation, follow-through) were literally codified by Disney’s Nine Old Men during the cel era. Every buttery-smooth micro-interaction in your banking app owes a debt to those painters hunched over light tables in Burbank.

The Frame Endures

Cel animation, as a physical practice, belongs to a bygone era, concluded by the last hand-painted frames of Disney's Winnie the Pooh in 2011. However, to view it as obsolete is to miss the point entirely. Its true legacy is not in the cellulose acetate cels themselves, but in the fundamental framework for creating complex, engaging visual systems.

Cel animation reminds us that sometimes the slowest, most labor-intensive method produces the most soulful result. We are in an age where AI can churn out motion in seconds, the deliberate, human touch of painting 150,000 individual frames still stops audiences in their tracks.

Whether you’re building the next billion-dollar animated franchise or simply want your startup’s onboarding animation to feel premium, understanding cel animation gives you an unfair advantage. It teaches weight, timing, and emotion in ways no tutorial on After Effects ever will.