A chapter from this is available:
Nitrate Won't Wait: A History of Film Preservatin in the United States by Anthony Slide (1992)
one hit for 'George Lucas' (SW comes up blank)
A few directors tried to press for clauses in their contracts requiring producers to make black-and-white separation masters on their films. Ironically, the only directors who could enforce such clauses were those, such as Steven Spielberg and George Lucas, whose films were so popular that it was in the best interests of the producers to make such master.
But from the Lucas/Nolan statement a few posts back it sounds like Fox didn't complete this part of the contract...