Ask the Expert Question-and-Answer Archive

by Ron Joseph

May, 2004

Paint Toners

Q. My question is in regards to paint toners. Here's some background info before I get to my question.

I had painted a vehicle a few years ago as an ongoing restoration. Just recently the owner has returned to have more parts painted. He brought back the paint that was initially purchased and used on the car . It's PPG's single stage DAU paint. It's a light gray in color. The paint can was sealed and stored in a cabinet. I decided to check the color by spraying out a paint sample. After it dried, I put it up to a part painted a few years ago (the part hadn't been exposed to the environment), to my surprise the color was off! This is the second time this has happened to me and only with light solid colors.

Now, my question is: What happens to paint toners in the original paint can that has been left in storage for months/years etc.,? I'm aware toners have a shelf life but what can I do to prevent this color shift - other than paint the entire car within a certain time window but with so many ongoing restorations it's difficult to paint the entire car at one time. The customers cars we restore take a few years or longer to restore/paint etc., depending on the type of restoration. Any help would be appreciated.

Thanks Ron!!

Sincerely,

Ernie

A. Paint products do change over time. Most of the time paint products have a shelf life of about a year because of the stability. You did not mention if you added any solvent to the old paint to make it spray.

In addition to all the possibilities for change, a major concern is the pigments used to match the color. You stated the paint was light gray in color; beside the prime pigment which is white, there may be a 3 or 4 other pigments used including the black. As this combination of several pigments ages, there are chemical changes taking place. The pigments are being soaked or wetted at different rates causing the visual change. Also consider the 2 or 3 years between the initial spray application and your sample panels.

Unless all the variables, viscosity spray gun, air pressure, the applied thickness are considered, I would be surprised if the sample panel did match the original parts.