Printing presses whether they're an older manual model (like the one pictured) or a modern computerized system, share one purpose in common - they must be able to lay down a film of ink with remarkable precision and consistency.For a typical offset press, one ink tower delivering one of the four primary colors in full color printing lays down an image covering an area approximately 40" x 28". That image is formed by splitting a film of ink 4 microns thick (a tenth the thickness of a human hair) twice (plate to blanket then blanket to paper), while at the same time emulsifying it in a chemical solution (made primarily of water) to a depth of a few molecules. Too much water and the ink washes away. Not enough water and ink starts to print in the background. The ink is carried by approximately 19,250,000 halftone dots averaging in size from 10 to 60 microns. The final film of ink deposited on paper over the whole 1,120 square inch area of the image and is held to a thickness of about 1 micron (one fortieth the thickness of a human hair) with a tolerance of +/- one-tenth of a micron. The positional accuracy of the image is held within one-three hundredths of an inch - about 40 microns. All in one quarter of a second on press.
Woow, this is great post Gordo written in a way that can be useful and fun for anybody .Even my son (10 years old) who is by my side now asks me how thick is his hair and how we can measure that.
ReplyDeleteGordon,
ReplyDeleteImage thickness control looks impressive. In absolute terms it is a small value. But variation is important too.
You have a variation of +/- 0.1 micron on a 1 micron thickness. This is +/- 10% or a total range of 20%. This is not a very good or tight tolerance relatively and that is important too.
Presses are relatively good at spreading a little bit of ink over a large area or an even smaller amount of ink over a small area but not so good at controlling the variation of that ink thickness because it can't control the amount of that small bit of ink with tight tolerances.
Never the less, the printing process is always so amazing to see.