Press trick using spot color. Spot color inks use opaque bases primarily. A trick we used on press was to keep halftone clear base nearby. By adding a tiny bit of this to the ink in the screens you can manipulate how secondary and tertiary colors form. It literally expands the colors in the print to get those halftone overlay areas to make great secondary color. The transitions from say red to yellow bring out shades of orange that wouldn't appear otherwise. This can also help balance color in the design. If it is too red, keep adding halftone base to the red until the color cast of red is reduced. We came upon this for the first Lord of the Rings movie where the poster we had to match had tons of different colors. We spent a half a day tweaking the inks in the screens with halftone base. Time consuming, but faster than redoing seps, new screens, and starting again with the halftone base to balance the print to match the poster. Halftone base only, it's perfectly clear, and prints a better dot which helps spot color that can be thick and build up on subsequent screens in the print cycle. Also helps to use mesh counts in the 300-350 range that put down less ink so the translucency of semi opaque inks can accomplish this technique easier. You can keep a digital scale by the press to note additions of halftone base. We put in X grams of spot color, then a teaspoon at a time weighed onto an ink card (on the scale tared out to 0) then kept a running total of gram additions, then scrap it off with a spatula onto the set up screen. This helps to be able to start mixing gallons that have the same ratio of clear base to spot color as the job progressed
