Hi Macky
Two more cents worth......
On one hand, some ink companies (i.e. Union and Rutland Plastisols) have their own primary color range and a computerized formula guide that give you recipies for a given PMS#.
In most cases, they make the software available for free:
http://www.unionink.com/software/software.html http://www.rutlandinc.com/new/download.htm#download
On the other hand, some ink companies (i.e Matsui Waterbased Inks) use Pantone's primary color range where you can directly use the fan deck as a guideline or employ their computerized version:
Matsui-Color | Color Matching System
Although we're a certified matching center for all three, I'll admit that we default to Rutland M2000 if given the choice
.......more formula variation choices for the advanced color-matcher.
Most distributors offer quart size mixing kits from a variety of manufacturers to help get you started.
Earlybird tip: all PMSystems will use relatively larger amounts of yellow and white as higher use primarys.
Happy trails!