Doing a simple design with Speedball acrylic. Basically what I have is a neon green background with a black smiley face in the middle. My question is there any noticable difference between printing the background as a solid rectangle and then overprinting the face after the neon green dries or would it be better to use color seperation and print each color as spot. Basically what happens if you overprint a layer of black onto of another color.
As long as the color being over printed is dark and opaque I like to over print. You should have nothing to worry about with speedball black, but to be sure or in the future with different colors you should always do a little test with the inks you'll be using. This is also the basic idea of trapping.