[rotorwrench]

When matching by eye, the person doing the mixing doesn't always carefully measure the amounts of different base colors that go into the end result. If that person did make carefull account of the tint bases for a given quantity, there would be a formula that could be replicated. It's too bad that someone hasn't taken on this task for some of the more popular colors of the more popular cars but this might be a daunting task even with a handfull of colors let alone the hundreds of different colors used between 1929 and 1959.

One thing that would help in making formulas would be to start with modern (as new as possible) chips in one brand of product and get close with chip formulas then add to the formula for a match taking account as the process progresses.

I just go through my Dupont (since that just happens to be what I'm used to using) chip charts and pick something that's close to the eye and that's what I use. At least I can get the stuff replicated if I have to do a repair later. This practice keeps me sane. Otherwise, my obsesive compulsive side takes over and I regress into a drooling idiot.