The art of Process Control pt 2- Fingerprinting
Each person’s fingerprint is unique. That’s why they are so useful for identification purposes. In the printing industry, each press has it’s own unique set of characteristics. That is why presses need to be ‘fingerprinted’.
A fingerprint on a press means that a test form is printed and then the resulting image on those sheets is analyzed for a variety of things.
The image on the left is a typical fingerprinting form used by printers. There are a variety of targets and images on a fingerprinting form, and each one has a specific purpose.
There are many targets that are placed on a fingerprint form. Below is a partial list and what they are used for:
- Color Bar- used for measuring solid ink density of Cyan Magenta Yellow and Black inks. Can also have targets for Trap/overprint density, dot gain and slur (doubling)
- Profiling Target- A profiling target is needed on the form, because once the printing condition is verified as accurate, then the targets are used to create an ICC profile for color.
- Visual Targets- Since print is a visual medium, you need images to accurately judge how images will reproduce. There are several standard images used on fingerprint forms. They usually consist of several 4c images, and at least one grayscale.
- Line and Text Targets- These are used to check what the smallest size text and lines can be accurately printed- in single color, 3c and in knockouts (white in a black field)
- Gray Finders and Color Ramps- these targets are used for computing the best neutral 3c gray balance as well as dot gain per ink unit.
Typically, anywhere from 500 to 1000 sheets are printed, and then 10 from throughout the entire run are checked and all of the data on the sheets analyzed. Sometimes, after looking at the press sheets, you have to go back to step one and adjust the curves on your plates to insure that the final print is what you are aiming for.