During the beginning of the film when Dallben uses Hen Wen's magic to find the Horned King, the first image that appears in the water was a recycled section from "The Night On Bald Mountain" sequence from Fantasia (1940).
This was the first (and last) movie since The Jungle Book (1967) where the old multi-plane cameras were brought briefly out of retirement (with a few improvements this time). New technologies such as computer-generated imagery now available to all studios have made multi-plane photography obsolete.
The production of this film can be traced back to 1971, when the Disney Studio purchased the screen rights to Lloyd Alexander's "The Chronicles of Prydain". The film took over 12 years to make, 5 years of actual production, and cost over $25 million. Over 1,165 different hues and colors were used and 34 miles of film stock was utilized.
This was the first animated Disney movie to be filmed in widescreen since Sleeping Beauty (1959). Movies released prior to The Black Cauldron (1985) and after Sleeping Beauty (1959) involved matting of the top and bottom of the filmed image in order to make a widescreen image suitable for the movie theatres.
The first Disney movie to not have "THE END" at the end of the film. Instead, it just goes straight from the final scene to the closing credits of the movie. A few later films, such as The Great Mouse Detective (1986) and Aladdin (1992) would have "THE END" appear before the credits roll, but this was for a special occasion usually.
Tim Burton, who worked as a conceptual artist on this film, wanted to incorporate minions of the Horned King that were akin to the "facehuggers" from the Alien movie series. Some samples of his work can be seen on Disney's 2000 DVD of this title.
The management team at Disney changed during Cauldron's production. New studio chairman Jeffrey Katzenberg screened the mostly-completed film and was appalled by its darkness. He suggested editing the film, and when producer Joe Hale protested (animated films are typically not edited in post production the same way live-action films are), Katzenberg himself brought the film into an editing bay and began cutting it himself, ultimately extracting three minutes from the final run time.
The movie is loosely based upon the first two books in Lloyd Alexander's Prydain Chronicles ("The Book of Three" and "The Black Cauldron"). The Chronicles, in turn, are loosely based on the mythology of ancient Wales, a collection of tales known as the Mabinogion.
A technological breakthrough in this movie was the development of the APT (Animation Photo Transfer) process. The first major change in the Studio's method of transferring the artist's drawings to a cel since Xerox copying replaced hand-inking over 20 years earlier, the APT greatly improved the quality of the animator's art. Dave Spencer was awarded an Oscar for his development of the APT process.
Video cameras gave animators and directors an immediate and inexpensive record of what their efforts might look like. The dimensions and volume of the objects were fed into a computer and then their shapes were perfectly maintained as their movement was generated by programming.
According to former Disney animator Michael Peraza Jr., there were multiple openings that were conceptualized by different people. Peraza worked with art director Don Griffith and artist Vance Gerry on one version that showed the Horned King and his gang burning down a village. Sweeping flames were used as transitions between scenes of destruction. Mike Peraza and the artists wanted a contrast to the peace and quiet of Taran's farm life.
According to animation artist Michael Peraza Jr., when Disney started having screenings for the public at the studio theater to gather their reactions to the rough cut of this film, he knew that the "un-dead" section would most likely be revolting to some in the audience who would not expect to see a bunch of rotted corpses slowly fermenting. When the film reached the "un-dead" sections close to the end of the film, the doors opened and a mother was angrily leaving with her two wailing children. She was followed by another, and soon there was a sizable exodus of crying kids and upset parents fleeing from the theater. So the un-dead sections were quickly cut from the film.
According to producer Joe Hale, "When [Jeffrey] Katzenberg first screened the film he told us to cut it by 10 minutes. Roy [Disney] and I got together and found some scenes we could get rid of that didn't affect the story that much." When they ran it again for Jeffrey Katzenberg and the film finished he asked Roy Edward Disney, "Is that 10 minutes?" When Disney replied that no it was only around 6 minutes. Katzenberg stated, "I said 10 minutes!" Hale continued, "Eventually he cut out about 12 minutes, which really hurt the picture."
According to Animation artist Mike Peraza, Disney showed this film to the public at the studio theater to gather their reactions to the rough cut of this film. But the reactions of the audience were mostly negative due to the dark content of the film. So some scenes were cut from this film.