EDIT: I've altered the title of this thread to be more specific to dyelines and cactus prints for the original Star Wars movie. But it's really purposed for any sort of print used in the production of the movie Star Wars. Many of the techniques used in producing Star Wars, were fairly unique to this particular movie, and although the same sorts of prints were used on other productions around the same era (Battlestar Galactica, for instance), by the time The Empire Strikes Back was being produced, much had apparently changed, including the use of dyeline & cactus prints.
Preamble - My Personal Interest in the Subject
I was 10 years old in 1977, when my dad took me and a friend to the local theater to see Star Wars for the first time. As a kid I was deeply fascinated with the behind the scenes stuff that went into the production of the special effects for the original Star Wars movie. I loved building plastic models, and I dreamed of working at the ILM model shop. So it's no suprise my collection has begun to reflect those interests I had as a kid.
As a collector, I love delving into the history of the items I collect. I make it a practice to try to get to know where they came from, who they came from, and how they relate to the movie I loved so much as a kid. So my limelight photos will be accompanied by other material that explains their place in history. I enjoyed learning about these pieces, and I hope you will also enjoy seeing these items, and perhaps learning something about their place in SW history.
Joe Johnston's Sketches
In August 1975, Joe Johnston was hired to work as a storyboard artist at the newly created ILM (Industrial Light & Magic). He soon became one of the primary artist working on the pre-production material, along with Ralph McQuarrie. Joe Johnston would refine some of the designs that Ralph McQuarrie & Colin Cantwell had worked on, creating his own sketches of the various vehicles & spaceships to be used in the film. These sketches by Joe Johnston would be used by both model builders & set builders at Elstree Studios in England, where primary filming was to be done. Often his sketches would also be used as the basis for more detailed technical drawings and blueprints. The original sketches were created on vellum paper.
One of Joe's earliest sketches was of the rebel 'Pirate Ship', what was later to become known as 'The Millenium Falcon'. I believe the original sketch is locked up in the LFL archives. A picture of it can be seen on page 72 of the book "The Making of Star Wars".
Early 'Pirate Ship' Sketch by Joe Johnston (see reference  below)
The early 'Pirate Ship sketch' actually has quite a rich history, in that it was a concept piece for the original Millennium Falcon (see reference  below), and after the Millennium Falcon was re-designed in late 1975/early 1976, it later became the Rebel 'Blockade Runner', Princess Leia's ship, the 'Tantive IV'. As the story goes, Lucas was in England when it came to his attention that the 'Eagle' spacecraft from a then new British television sci-fi production called 'Space:1999', somewhat resembled the design for the original Millennium Falcon. This bothered Lucas, and he ordered the Millennium Falcon be re-designed. This was just after the giant 6'+ model had been completed back at ILMs model shop. Quite a bit of the model shops budget had been put into the now rejected design & model. Later, when it was determined that they would re-use the design as the 'Tantive IV', the scale of the model was then altered, and a new cockpit and other pieces were designed for the ship.
Many years later, during the production of the prequel movie "The Phantom Menace", this early concept sketch also inspired the design of the ship Radiant VII, which transported Master Qui-Gon Jinn and Obi-wan Kenobi at the beginning of the movie.
Dyeline (Diazo) Prints
Of course, if Joe Johston's sketches were to be used as reference for the production of the movie, they had to be duplicated for distribution to the various departments. So 'master' copies of the sketches were created using a form of printing known as 'dyeline' or 'diazo' printing.
Dyelines were created by passing UV light through the translucent vellum paper of the original sketches. The UV light then struck a special paper known as 'diazo', that was UV sensitive, and would lighten (whiten) where exposed directly to UV rays. The ink on the original sketch would block the light in places, casting a shadow of the sketch, onto the diazo paper. This left the diazo paper 'unexposed' (blue) wherever the shadow of the original sketch fell on it, creating a 'blue line' copy of the original sketch. Dyeline prints were also sometimes referred to as 'bluelines' or 'blueprints' (though they are more like a reverse blueprint).
These dyeline prints of Joe Johnston's artwork were used as a type of 'master' print/proof. Although they were sometimes used as reference for model/set building (see reference  below), they were mainly held by the ILM and Studio executives, and used to create other less costly mimeographed prints. Dyelines were produced in limited numbers, and as a collectible, are sometimes as close as you can get to the original sketched art.
The Pirate Ship Dyeline Print
The following dyeline print was created from the original artwork, as early as mid 1975, and was used during the production of the movie Star Wars. It was obtained from an ILM source, and provenance is direct from that source.
The early 'Pirate Ship' (Millennium Falcon) model was the first of many built for Star Wars, in the later half of 1975. So material related to its construction dates from that period.
The Star Destroyer Dyeline Print
The following dyeline print was created from the original artwork, sometime in 1975-76, and was used during the production of the movie Star Wars. It was obtained from an ILM source, and provenance is direct from that source.
The Star Destroyer model was one of the last to be readied for filming. Due to time constraints it was largely built using a cactus print of this particultar Joe Johnston sketch as reference. This is supported by the following references:
- Imperial Star Destroyer info found on Page 5 in The Star Wars Sketchbook (see reference  below).
- Cactus print of Star Destroyer sketch on workbench, seen in image used on page 90 in Sci-fi & Fantasy Modeller, Volume 5. (see reference  below).
Later, in 1977, after Star Wars had been released, Joe Johnston produced a book based on his sketch work, titled "The Star Wars Sketchbook". Both of the above dyeline prints were also used to create the exact related images in Joe Johnston's book.
Relatively speaking, dyeline printing wasn't the cheapest form of printing available. So when further copies of Joe Johnston's artwork were needed for distribution, they would use the dyeline prints as 'masters' to create mimeographed prints of the same sketches. The paper used for these mimeograph prints has an interesting feature. On the backside of the paper are small cactus symbols, similar to watermarks. Since most (but not all) of these mimeograph prints feature one or more cactus symbols on the back, they are often referred to as 'cactus prints'. These cactus prints were distributed to various crew members to be used as reference material for model and set building (see reference  below).
The 'Pirate Ship' Cactus Print
The following cactus print was created using a dyeline print, and was used during the production of the movie Star Wars. It was obtained from a source related to the British film crew working at Elstree Studios in England, where most of the principle filming took place. It may have been used as an early set building reference, since a life sized version of the Millennium Falcon was to be built in England, originally based on this early 'Pirate Ship' (Millennium Falcon) design.
Sets were built to replicate the cockpit of the Millennium Falcon. Preparations for princple filming, including set building, were already underway in England when Lucas ordered a design change for the Millennium Falcon. Thus several key pieces of the old Millennium Falcon model were removed from the model, and used in the new design and model build. These included the cockpit, and the radar dish. As you can see in the early Joe Johnston sketch of the 'pirate ship', the cockpit is very similar to the one designed into the final version of the Millennium Falcon. Here's another look at the the original Millennium Falcon (see reference  below) model, with its distinctive cockpit intact.
Cactus Prints In More Detail
In response to a question in another thread, I put together some more detailed information about 'cactus prints', and their nature. I hope this helps to show the difference between these genuine production prints, and lower quality, or more modern, non-production copies.
The cactus print paper has contrasting appearance and textures on either side. The printed side feels waxy, and appears semi-glossy. It's also more white. The backside is off-white, and both non-shiny & non-waxy. Almost like a finer grade of newsprint. The back side often has one or more faint cactus watermarks.Originally Posted by lkraan
I should also mention that I am describing the print as it is today. I am uncertain whether the contrasting nature of the paper's front & back side are completely due to the processing of the paper stock, or whether some of it is due to the mimeographing process that created the image, or how much should be attributed to aging. I recall in art class, we sometimes applied a waxy coat to ink sketches to help preserve the image, which might also keep the paper whiter over time.
Here's some pictures that let the light play on the surface of the print. Also, in the second print, you can see how the same light plays on another surface before it reaches the print. The other surface is a semi-shiny poster board, and yet the light shines even brighter off of the cactus print, even though its farther away from the source. Then finally a few pictures showing the cactus logo/watermark, and showing the location of these on the back of the print. The light black circles are added to the picture to help show the location of the cacti marks. As I understand it the cacti don't always appear on the print backs at the same frequency. This print has three. If I recall correctly, another collector, who has had some 300+ various production used pieces in his collection at one point, mentioned that some may not have the cactus, or they may just have one. I'm not sure what accounts for the varying frequency the cacti appear on each print sheet, but it may be that the placement of the cacti on the paper stock is inconsistent, and the sheets may come from a roll of paper stock that may have been cut to varyng lengths during processing (just a somewhat educated guess on my part - I live and grew up in paper mill towns).
The print's nickname 'cactus print' comes from the cacus logo that is frequently found on the back of the paper stock. Hopefully this description and these pictures are helpful.
 The soft cover publication "Sci-fi & Fantasy Modeller, Volume 5" which features an article entitled "A Boy, a Girl, and a Universe... A Look Back At The Making of Star Wars - 30 Years Later" by Paul Taglianetti and Gene Kozicki. Published in 2007. Particularly pages 80 & 90, which feature images used above.
 "The Star Wars Sketchbook", by Joe Johnston. Published in 1977.
 "The Making of Star Wars", by J.W.Rinzler. Particularly pages 71 & 72, which feature images used above.