Automotive Paint Colors: What Affects Color Match?
Why is auto paint color match such a difficult task?
Automotive Paint Colors: What affects color match?
In this article I will be discussing the main factors of why color match is such a difficult task. I believe if you can grasp a little bit about what auto paint colors are made of and how their application shifts color, then you could understand what causes color to change and what you need to do to match them.
There are three basic ingredients in automotive paint:
The resin is the component that holds together the pigment in suspension, provides adhesion to the surface applied, and determines the quality and paint durability.
The pigment comes in a powder form similar to concrete, and the average aftermarket automotive paint mixing system includes about 100 colors or toners to be able to mix formulas including metallic and pearl paint colors.
The solvent is what provides the transferability, without the solvent the paint would be to thick in viscosity to transfer from container to container.
Now that you know the three basic ingredients, let’s talk about the different paint systems and the applications for each.
Prior to 1985, the majority of the domestic cars had single stage paint from the factory. This was a major problem in trying to match the metallic colors for several reasons. In single stage metallic paints, the paint film is all one layer combined including the gloss resin, pigment, metallic and solvent.
The painter was challenged in painting a single stage metallic system because he only had 4 coats to achieve coverage and layout the metallic in a uniform matter by dusting light coats but still maintain an acceptable gloss.
This challenge was overcome by applying the first and second coat medium wet to achieve coverage and good bond to the surface. The third coat was applied medium wet and immediately followed by a mist coat until the metallic was even. The painter had to move fast and paint panel by panel and jump side to side to keep the overspray melting.
The secrete to this application was to keep the paint film wet, so when you mist the metallic on the wet surface it would flow to the bottom of the paint film and let the gloss resin rise to form the glass look we were looking for.
The same process is used in basecoat colors today except we are not worried about gloss because the urethane clearcoat is applied as the final topcoat and provides the deep gloss we need.
So what affects color match? Now that you know the ingredients and application process of automotive paint, I will explain what happens to color during the application.
Auto paint colors are made up of a combination of pigment colors and metallic sizes including pearls. The first challenge is the factory standard. Today, the average paint code has between three to seven alternates that are worth formulating. There is actually more but the auto paint manufacturers have narrowed them to down to keep the databases simple to use.
So why do the car manufacturers have so many variances? Most car manufacturers have three major paint suppliers. The manufacturer decides on a standard color for production and submits a painted sample to their suppliers. The paint manufacturer then produces a formula for the “standard sample” and is allowed a tolerance of plus or minus 5% when they deliver the paint.
This is the first problem because the plant in the east coast may be getting a 5% shade greener on a blue metallic standard and the plant in the west coast may be getting a 5% shade violet on the same blue metallic standard. When compared side by side, they look like a completely different color. This is the reason the paint manufacturers usually have the standard formula followed by two alternates. If the alternates are not available, the painter in the body shop usually mixes the standard formula and tints it accordingly.
The second reason for variances in paint colors is the metallic color applications. The metallic colors are now classified in 7 categories. Extra fine, fine, medium, medium coarse, coarse, and extra coarse. The metallic colors control the value (lightness and darkness) of the color similar to what white does in a pastel color.
Metallic colors will cause variances in color when applied. Temperature, paint film thickness, flash off time between coats, fluid tip sizes, speed of the spray gun, surface type (Plastic or Metal) and humidity will all cause the color to shift lighter or darker.
The rule of thumb: the longer it takes to dry, the darker the color will change as it dries. This is caused by pigment floatation. The metallic flakes will settle down to the bottom of the paint film and push the pigment up causing the color to shift darker.
The reasons above only mention the variables at the car manufacturers level. So what happens to a color after three years of sunshine? Many people think that colors do not change, but they do, and I will prove it. If you own a car that is at least three years old and has been out in the sun most of the time, remove a pinstripe and you will see the original color when you bought the car.
The sunlight has ultra-violet, and has absorbed some of the pigments. Blue metallic colors sometimes shift to a greener shade, and reds will turn pinkish or more orange. The auto body shop has to deal with matching an oxidized color in addition to new OEM colors. The new paint to be applied will look brighter and cleaner but the rest of the car looks dead even if you polish it.
Auto Body Shops today have a greater challenge than just color match. The texture or (Orange Peel) also has to match the original finish in order for it to look pre-accident condition. This can be accomplished by using the proper spray gun, polishing equipment and experience.
Why do plastic bumper covers change color? Every once in a while we get a phone call from body shop client that is trying to deliver a car and their customer will not take it because the bumper looks different than the car. The most amazing thing is that the bumper and the front end of the car was painted at the same time, with the same gun, same air pressure, same temperature and the same paint.
How do you explain the bumper color change to the customer? Plastic bumpers will always change color especially in metallic colors. The plastic has a static charge and the metallic paint will settle different than on the sheet metal parts, causing pigment floatation that will shift the color darker or lighter. The other reason is surface temperature, if the sheet metal is colder, the bumper will look lighter, if the sheet metal is hotter than the bumper, the color on the bumper will look darker. The third reason is flex additive. If the clearcoat is applied on the bumper with a flex additive, it will shift the color slightly.
How do you prove your point after explaining this to the customer? Your customer will probably think your trying to fool them with this explanation, Luckily, the majority of our body shop clients in our area are dealerships. So they walk the client to the show room floor and point out that just about every car on the lot with a metallic color has a shade different on the bumper covers, front and rear, plastic door handles and plastic mirrors, all have different shades. Most clients are more at ease when they realize that they bought the car this way but had never noticed.
Here are some tips you should consider when spot repairing:
Always blend the color to achieve color match. Do not panel paint and expect a quality color match, even if it looks close enough, blend it! You have too many variables to deal with.
Always tint the value first before tinting the hue. 80% of the time it will hit or it will be bendable. Never try to blend a color that is off on value, it will always look to dark or too light where you spot repaired.
Auto Body Supply, Inc has been in the automotive paint industry since 1969.
Raul Jr.
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