When your job is started on our printing press it goes through a process called make-ready, or MR. Make-ready consists of two major tasks, getting register to fit and getting color to match. The MR process will vary but for each plate takes about 15 minutes and 200 sheets. Once MR is completed, the actual production run begins printing.
Each process color, CMYK, is imaged onto a separate metal plate by computer-to-plate or CtP. To mount or hang the plates onto the press the plates are first punched and bent to fit onto the plate cylinder. During MR small test trials or samples of about 100 sheets each are printed, we call these pulls. The goal is to get the separate plate images to superimpose on top of each other so their register fits. This makes images look sharp, crisp, and in focus. Register tolerance of less than one full row of halftone dots is about 0.006” at 175 lines per inch, or Lpi. Smaller and thicker sheets with less ink coverage usually register better.
Color is achieved by adjusting the amount or thickness of ink first applied to the ink rollers, then plate, then rubber offset blanket, then finally onto the paper. Adding more ink makes the color darker and less ink makes the color lighter. While we have software and hardware technology that assists in achieving color, such as ink key presets and closed loop scanners, setting color still requires the art and craft of experienced technicians who visually compare the degree of color match between press and proof. The ink film thickness is measured with instruments called densitometers that measure optical density. Our presses have been calibrated to comply with international printing standards, such as ISO, SWOP, SNAP and GRACoL’s G7. Solid ink density tolerance is 0.10 units darker or lighter, this should produce consistent color. Density is used as a quality and process control metric to set the initial color, check for uniformity and evenness across the sheet (important for crossovers), and monitor consistency throughout the entire press run from beginning to end.
If you have any questions about this article please contact Steve Suffoletto at firstname.lastname@example.org.