Via Starwars.com:

WHEN IT CAME TO CREATING THE EFFECTS OF THE ORIGINAL TRILOGY, THERE WAS NO QUICK AND EASY PATH.
Creative wisdom says that unless you’re willing to invest the necessary amount of enthusiasm and labor into your project, then you might as well walk away and never look back. The original Star Wars trilogy remains a testament to this adage as it continues to ignite the imagination of aspiring filmmakers — and it’s obvious why: creator George Lucas and all hands involved pushed themselves beyond their physical and mental thresholds to blur the line between fantasy and reality. It was clear during Star Wars’ early stages that Lucas intended it to be an unparalleled experience of onscreen magic, and in order to achieve such verisimilitude, meticulous attention was poured into its visual effects (perish the thought that someone sees the strings and shatter the illusion). Some effects were more arduous than others, but few compare to the following that were responsible for so much blood, sweat, tears, and aching muscles.

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