Quote:
Originally Posted by buckydent
The infamous "suntan" variation appears with cards throughout the 70's.
I think it's just ink changing or worn plates on the duller/ off color ones .
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My father was a pressman for 20 years and I myself became certified in off-set presswork years ago and did nothing with it.
The final color run in the CMYK printing process is and always will be K (which is black). Black is used for "trapping" which is a method of overlapping colors to fill in color gaps. After a color plate is switched and a new color run is started it generally takes about 25-50 sheets before the water in the press evenly distributes the ink from the rollers to the plate. During those first 25-50 sheets you get a slightly heavy dose of whatever ink you're getting ready to print.
All that to say this, in the "Sun Tan" variations you are finding cards run from sheets during the beginning of a black ink run making all colors throughout the print slightly darker. Once the run hit its stride it produces the normal variation. Pressman are supposed to throw the "error variations" away but they didn't sit there and look at each sheet. They usually know about how many sheets are bad in the beginning of a black ink run and, running on autopilot, just grab a small stack and throw in the discard pile. The "Sun Tan" cards are minor ink variations that slipped through the cracks.
Another less likely possibility is the pressman wasn't watching the water levels on his press and as the press slowly ran out of or ran low on water and the black ink became more prominent making the cards look darker. This usually occurs in the middle of the print run making it more difficult to remove the inaccuracies from the middle of a stack.