This is the best article I have found describing the dissection of the o-neg:
As a consequence, the restoration team was forced to struggle with a negative that was not only dirty but badly worn, from making thousands of prints, and was seriously faded, even though it had been stored at prescribed temperatures and humidity in a vault 650 feet down in a salt mine near Wichita, Kan. Blue skies and rich blacks had lost their luster. Silver had almost vanished from the emulsion in certain scenes, like the prelude to Kenobi's duel to the death with Darth Vader. Flesh tones had turned pallid. Strobing effects and those red fluctuations had mysteriously appeared. Some parts, such as the Tatooine desert sequences shot in Tunisia, had never had much luster to begin with. ("Star Wars," it's useful to recall, was first considered the slapdash work of a brash young upstart.) Other pieces weren't even original negative, but intentionally degraded duplicates that Mr. Lucas had stuck in to avoid emphasizing the quality of adjacent optical effects, some of which were so crude as to be almost unacceptable.
Tom Christopher, the Lucasfilm editor in charge of restoring the "Star Wars" trilogy, describes the team's three-year travail as deconstruction; another term might be Herculean, as in those nasty stables. Each optical effect had to be taken apart, layer by layer, link by link. Gaps and defects were replaced by original trims and outtakes, which Mr. Lucas had kept in his own vaults. Precious pieces of negative were washed, rewashed, matted, filtered ("We were handling the Holy Grail!" Mr. Christopher says), chemically or optically manipulated when possible, replaced with other original or duplicate material when necessary. Eventually 748 of the 2,228 shots in the movie were redone in the course of creating a new negative, from which some 2,000 new prints have been struck for the current national release. (Similar though less extensive work has been done for the two sequels, "The Empire Strikes Back" and "Return of the Jedi.")
When I met Messrs. Christopher, Gagliano and Briggs in a projection room on the 20th Century Fox lot in Los Angeles earlier this week, they ran a demonstration reel of their work. Side-by-side, before-and-after comparisons of a dozen or so shots convinced me that they'd done wonders, albeit incomplete ones. "It can't be a perfect restoration," Mr. Christopher acknowledged, "because you can't go back 20 years. But this film has a heart, which is what we hope audiences will respond to again. This is a film that lots of people remember in the same way they remember key moments of their lives; they talk about the day they first saw 'Star Wars.'"
http://online.wsj.com/article/SB854660380658056000.html?mod=googlewsj