Choke and Spread

Offset printing system depends on transfer of ink from plate to offset blanket and then from blanket to paper.    Depending on how hard the pressure is set between each contact, ink spots are easily squeezed to fatten to produce darker than desired image.       In order to compensate such "gain", halftone dots are reduced in size matching the printing machine's characteristics.      It is easy nowadays to do this by simply adjusting  tone reproduction curve on film/plate scanner but in 1980's there were no such digital equipment so that printers had to struggle to adjust (reduce) the dot size by adjusting exposure during the contact duplicating process.       Depending on what the final plates is used, either choking (thinning the edge of dots of positive film for positive plates) or spreading  (fattening dots to squeeze openings for negative plates) were used.      And in 1980 duPont promoted the use of daylight film saying it reduces waste due to the bright lighting condition rather than the darkroom condition when regular high sensitivity film was also used for contact purpose.        Seeing this to be a new trend Clark R&D focused on the development of daylight film, DLD and DLP around the time when I arrived Clark.        When Al Wietling kindly sent me a bunch of samples, they brought vivid memory of how Gene Wilkerson with his aids worked day and night to develop these film.      As I recall the duplicating film technology was a challenge but we came out with a superb product.        After 35 years we now know these were short lived but was a profitable technology for us.     I am sure most of the current members of graphic arts community would not recognize the word "choke and spread".     But those who experienced the challenge and battle of film world would chuckle and say we were there to meet the market challenge successfully
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