Is different colored ink applied to the plate all at once, is it done in stages, a different way? Thanks for any insight.
step 1 - pick up a box of Crayola 64 - not 128 and not 32... but 64! Step 2 - find a quiet place in which to work I think it is done in stages, especially with lithographed notes. they way the colors overlap on the chinsey done notes, makes me think that each color was done seperately. On some notes, there are parts that you know are not supposed to run into each other, but on notes that are really badly done (war time Iraq notes for example) you have an element slightly overlapping another on 1 note, but not on a second note. So i think at least lithographs are done in stages or something similar. But with all the different 'processes' in manufacturing notes... each could easily be done differently!
Traditionally printed sheets were run through the presses as many times as there were individual ink colors being used. Often so-called transparent inks were used, and deliberate overprinting of colors would result in the appearance of additional colors/shades. The mechanical challenges to precisely aligning the sheets for multiple impressions were successfully met many years ago. Usually multi-color printing has been done in a single run on Web presses, with multiple impressions as the paper travels from the roll to the sheet cutter. Alignment problems were pretty much insurmountable with trying to run a web that would re-roll the paper and allow it to be fed through again in the opposite direction with proper registration of the impressions. Your computer will print pictures with many colors and shades at the same time, although you have a limited number of ink cartridges, as a result of programs that open and close ink valves at ultra high speed. Most printing today is still done with traditional presses, but an increasing amount is being produced computer-style. The U.S. Bureau of Printing and Engraving, however, still uses presses that print one color at a time on pre-cut sheets of paper, and I've never seen any news stories or internet information indicating that any major world currency printer has abandoned that method. (So far as I know Bureau experimentation with web printing has ended, but I may be wrong on that count.)
During one of the summers while I wasin college I worked on the presses of one of the largest printers of junk mail. These were 16 color web presses that had 8 stations that could hold 2 colors on each. The engineering on these was incredible. Everything was done mechanically except the printing of the addresses which was by computer. The folding and packaging of the pieces were all done on the presses so that at the end of the line the product was complete, addressed and sealed in the envelope without ever being touched by human hands. Each color had a separate station on the press. Everything that needed to be that color was printed at once. The paper moved on to the next station where the next color was applied. The full color pallet was achieved by a complex system which involved varying the depths of the "plates" and mixing colors by applying them over the same space. The plates were rubber wrapped around a cylinder with the images and text molded on them. These ran through the ink trays and rolled the imageson the paper. Registration of the colors was key. Any overlap would produce a blurred image and wrong colors. One of the really cool things was the press did not stop for the changing of the paper rolls. One roll was on top and one was on the bottom. The roll that was not running had a piece of tape on it. When the roll that was running ran low, a button was pushed that brough the rolls together at the tape which picked up the other roll. A blade cut the old roll so there was a splice in the printing. The computer that printed the personalizations "knew" where the splice was and would not address the material that printed along with the piece that was spliced instead printing all ##### in its place. That way the splice was not sent out to a customer. What does all of this have to do with theprinting of banknotes? It is not the way the BEP prints notes but it may be similar to the manner in which notes that are offset printed are done.
