At the time it was made, it was hailed as the only live action film in which a human character makes no appearance. With the exception of some wide-shots of the Gelflings, it would've been the first live-action film where no human actors appeared.
Pre-production work revolved around Brian Froud's designs, without a finished script. When Froud originally presented Jim Henson with concept drawings for the crystal, Henson seemed totally perplexed. When Froud asked why, Henson said he had no idea what the designs were for. Froud had misunderstood Henson during early production conversations; Henson intended to call the film "The Dark Chrysalis," referring to the Skesis dominance over the world. Henson, however, loved the concept art, and integrated the idea of the crystal into the storyline.
Early drafts of the script featured Jen and Kira traveling through the underworld, where they encountered a race of underground mining creatures. The concept was later integrated into Fraggle Rock (1983).
Jim Henson's plan with the film was to get back to the darkness of original Brothers Grimm fairy tales. He felt that children liked the idea of being scared and that this was a healthy emotion for them to deal with.
Jim Henson personally trimmed 20 minutes from the film after a disastrous preview in San Francisco. He also ordered many of the character voices re-dubbed to eliminate some of the invented character languages, making the film more accessible and the plot easier to follow.
In February 1978, Jim Henson and his daughter Cheryl Henson found themselves stuck at an airport hotel when Kennedy Airport was struck by a snowstorm. They worked out the details of the film's world on numerous sheets of hotel note paper. The notes became inspiration for screenplay. Work on the film didn't begin in earnest until 1979, after the completion of The Muppet Movie (1979) which was shot in Los Angeles. This film was shot in England, back to back with The Great Muppet Caper (1981).
Conceptual designer Brian Froud was behind the look and feel of virtually every aspect of the film's production, from creatures and landscapes right down to the font of the opening title. In total, it took up five years of his life.
The name Jim Henson came up with for the planet on which The Dark Crystal takes place was 'Mithra'. When some people thought this sounded to much like a Persian god, the name was changed to 'Nithra', and then finally shortened to 'Thra'. However, the name is never mentioned in the movie.
It was Frank Oz's Idea for Kira to have a pet, Fizzgig, similar to Miss Piggy's little dog Foo Foo, who at that time had recently been added to The Muppet Show (1976). Jim Henson only reluctantly agreed because he did not like repeating himself.
The little hairy things that crawl across and that the Creatures eat are modified wind-up toy robots that run like crazy on two legs as a round rolling central body that houses the wind up motor. The wind-up key was removable.
Brian Froud based the Mystics on a previously designed troll from his 1977 book "The Land of Froud". In order to keep the two creatures separate for licensing purposes, he designed the Mystics to have four arms. This way Froud would keep copyright of his trolls while Jim Henson got the right to the Mystics. The Skeksis also have four arms, but their second set, a pair of tiny chicken legs beneath their shoulder blades, are mostly hidden from view. The only time you can catch a glimpse of them in the film is after the Chamberlain has been stripped of his robes.
The invented language of the podlings in the film and the character of Kira, when she is speaking to animals, actually contains a number of Croatian/Serbian/Bosnian words. They are poorly pronounced but easily intelligible. 'hvala vam', 'dobro', 'dodji', 'dolje' and others. They are not randomly placed either but are used properly in the situations.
The Special Edition DVD and the Blu-Ray disc feature several "workprint" takes showing early passes at dialogue. This early voice-over work differs from the final dialogue in several ways: the Skeksis speak in a foreign language, Frank Oz provided the voice of Aughra (sounding very similar to his voice work for Yoda in the Star Wars movies), and the Mystics were referred to by (presumably) their original name, the ur-Ru. The novelization was apparently based on this earlier version, referring to the "Trial By Stone" contest by its original name - "Hakskeekah" - and calling the Mystics the ur-Ru. In the final film, one reference to ur-Ru was not redubbed: when the Mystics enter the Skeksis Great Hall, SkekOk, the Scrollkeeper sees them and shouts "Ur-Ru!" Moreover, in the film's German dubbed version the Mystics are also referred to as ur-Ru. The filmmaker's decision to rename them came too late for the German dialogue track, which was already in the making at the time.
Originally the Skeksis and Mystics were supposed to speak in their own alien languages (the Skeksis version being a more crude version of the Mystic language) and David Odell developed words for the actors to speak on set. Ultimately, the only word in the Skeksis language that remains in the film is 'Haakskeeka', meaning 'Judgement by stone'. After the first test screening, British Sci-Fi writer Alan Gardner was brought in to write an opening narration for the film and Odell had to 'translate' his Skeksis dialogue back into English, all the while making sure the lines matched the creature's mouth movements on screen.
Two other actresses were considered for voice of Aughra. The first had to pull out and was never recorded. The second choice can be heard on the bootlegged 'directors cut' but she was deemed too difficult to understand by a test audience. Third choice Billie Whitelaw finally recorded the version as heard in the film.
Lew Grade sold his ITC Film Entertainment company to businessman Robert Holmes à Court who had no faith in the finished product, based on bad test screenings. As it looked like Holmes à Court was going to bury the film, Jim Henson bought the property back and funded its own release.
Jim Henson offered 22-year-old puppeteer Kevin Clash a job on the film, but since Clash was busy with both Captain Kangaroo (1955) and The Great Space Coaster (1981), he had to turn it down. Nevertheless, Clash afterwards became a regular member of Henson's puppeteer team, performing in several productions of his, notably as Elmo in Sesame Street media.
Jim Henson's original name for Aughra was 'Habeetabat'. Although he and screenwriter David Odell were fond of this name, Brian Froud was not. Froud's first concept sketches made the character into an ogre like character, so for a while she was renamed 'Ogra' before finally settling on 'Aughra'.
During production, the rumor mill suggested that the film was a huge folly and would be a disaster. Those theories were swiftly put to bed when the film began screening and audiences were completely awestruck by what they had just seen.
When Jim Henson and Brian Froud were still developing the story, they published a 20-page presentation booklet entitled "The Crystal" to pitch the film to potential backers. In this booklet, which is reproduced in the 2003 version of "The World of the Dark Crystal" book, all the characters and species save Jen have slightly different names: Skekses instead of Skeksis; Oo-urs instead of Uru/Mystics; Dee instead of Kira; Earth-People instead of Pod People and Garthem instead of Garthim.
In May 2017, it was announced Netflix is producing a prequel TV series to the 1982 film entitled The Dark Crystal: Age of Resistance (2018) and that the prequel mini-series will take place on Thra several hundred years before Jen embarked on his quest to find the missing crystal shard to The Dark Crystal. The prequel series is set to premiere in 2018.
Talented dwarf actors Mike Edmonds, Deep Roy, Jack Purvis, Malcolm Dixon etc. were used for the shots where the characters are seen walking, picking up objects, climbing and running, which they were dressed up as the characters in the film.
Director/puppeteer Frank Oz adamantly denies that he and Jim Henson ever considered ideas for a sequel, and has publicly denounced any attempts to make one. Nevertheless, The Jim Henson Company began touting plans for a sequel in the mid 2000's. Their plans finally came to fruition with the Netflix prequel series The Dark Crystal: Age of Resistance (2018).
In Bernie Brillstein's autobiography, he notes that Jim Henson originally did not want to license Merchandise for his children's show Sesame Street. He advised Jim Henson that the money could be used for projects he was passionate about. Years later when Bernie Brillstein had objections to The Dark Crystal's escalating budget, Henson reminded Brill stein of his own advice.
According to Duncan Kenworthy in the book "No Strings Attached - The Inside Story of Jim Henson's Creature Shop", the original idea was for the Gelflings to speak English, the Skekis in Greek and the Mystics Egyptian, the latter two being subtitled. This however is not reflected in footage from deleted scenes and the work-print, in which the Skeksis speak a fictional language.
It has been widely speculated that it was Jim Henson who directed the "good guy" scenes (Scenes involving the Gelflings, Mystics and other characters), and it was Frank Oz who directed the "bad guy" scenes (Scenes involving the Skeksis and Garth I'm) .