4 color CMYK VS Simulated or Spot color Separations
In order to compensate for the dot gain that is inherent with the textile screen printing process, the original RGB file must be converted and adjusted to allow for the excessive gain. Not only do the separations have to be adjusted but the press production crew has a set of very strict parameters to limit the dot gain to the absolute minimum. Many variables affect the success of the print. Specific guidelines dictating substrate, mesh tension, mesh count, line screen, squeegee pressure, squeegee sharpness, and durometer or contact and ink brand are just a few. The fact that we are printing with plastisol (which is basically plastic particles suspended in clear base) does not allow us to achieve the transparency of litho process inks.
4 color process printing on t-shirts can cause frustrating production runs by chasing the color, trying to balance the halftones, and eating up hours on press without good results. When the graphic has more secondary and tertiary colors than primary colors, it will be very difficult to balance the halftones to achieve the clean greens, browns, purples and neutral grays with no obvious color shift. In almost all cases spot color bumps are added to the 4 color process seps to help achieve the red, green and neutral gray in order to match the original art. Conceivably a 4 color process print with only 4 screens will cost as much or more than 10 or 12 color job due to the time and effort involved in printing it. In addition, 4 color process prints will usually fall short of the close color match and vibrancy that a simulated process spot color print is likely to achieve.