What to tell customers about metallic paint

Metallic paint coatings can add vibrancy and visual appeal to your project. Their lively appearance is caused by the way visible light reflects off the metallic flakes.

Variations in appearance
Be aware that the same qualities creating depth and brilliance also can cause variations in appearance within a project or even within a single part. Specifically, metallics can have variations in the level of brightness or dark and light areas. The reflective property of the metallic flakes means that the same painted surface will look different depending on the viewing angle, the angle of the light source—the sun—and the intensity and type of the light source. In addition, the general orientation and direction of the metallic flakes in the paint will also affect the brightness of the color. This is an undesirable but necessary reality of metallic paints, and is sometimes referred to as the “flop of the flake.” 

To better understand the optical dynamics of metallic paints, it is helpful to think of the flakes as tiny mirrors. The flakes that lie horizontal in the paint will reflect the most light. In an optimally applied metallic paint, the flakes all lie perfectly random. This achieves the greatest level of “sparkle” and depth.

Now consider the two extreme alternatives. If all of the flakes in the paint lie horizontally, the surface will appear bright and almost solid rather than “sparkling.” Maximum light is reflected back to the observer. If metallic flake content is high, the surface will actually appear to be solid color paint rather than a metallic.

In the other extreme, if all of the flakes stand vertically in the paint, little light will be reflected back to the observer. The surface will appear dark. Less sparkle will be seen as well.

Coil-coat and spray application
A consistent random flake orientation is the ideal medium. Achieving this is practical and realistic with “coil-coated” sheet stock. With a coil-coating process, virtually no application variables will be involved. Part geometry—continuous flat sheet—is constant, spray distance is constant and so forth. As a result, it is possible to attain a consistent random orientation of the metallic flakes, and a uniform color and brightness.

Unfortunately, a spray-application pro-cess has more variability, thereby reducing the ability to achieve perfectly random flake orientation. These process variables include different part geometries, electrostatic and grounding effects—even if electrostatic equipment is not used—fluid pressures, paint-to-part distances, overlapping spray areas and supplemental hand spray to reach recessed or corner areas.

As a result, spray-application of metallic paints, used on any aluminum parts other than flat sheet in stock colors, will often show some variation. Faced with this reality, the question for architects, owners, contractors and material suppliers then becomes how to manage and minimize the risk of metallic variation.

Minimize risk of metallic variation
First step: Recognize jobs that have the greatest risk. Jobs that have the following design or location characteristics increase the risk of visible metallic variation:

Bright silver metallics. Your paint applicator can advise you if the particular metallic color selected represents a higher risk.

Wide continuously painted surface areas. A job with lots of panels will more likely show variation than a job with aluminum extrusions such as window or curtain-wall framing, or a job with panels separated by masonry or other materials that break the continuity of panels.

Shaded walls. The same panel will show more variation in shaded light than it will in full sunlight.    

Large break metal panels. Fabricated or bent panels are much more likely to show variation than flat panels or sheets. The variables in the paint application process mentioned above become even larger with complex shapes and larger parts.

If your job has these characteristics, consider the following options to reduce the risk of job-site issues and achieve a more consistent appearance:

Paint all material at the same time. If this is not practical, at least paint adjacent parts at the same time.

Minimize the number of paint applicators on the job to give the project manager better overall control of color variations. Different paint applicators use different painting equipment, creating differences in color, especially with metallics.

Advise all parties—architect, owner, general contractor, glazier and so forth—up front that some degree of variation can be expected. Industry standard variation is typically two Delta Es, and samples of two Delta E variation can be provided to the parties involved to show examples of what that variation can look like. 

Request color sample chips from the applicator rather than the paint manufacturer. The painter’s application equipment can result in a slightly different color or appearance relative to the paint manufacturer’s samples produced in a lab.

Ask your paint applicator about alternative metallic colors. Some metallic colors are more prone to showing variation than other colors, due to differences in size of flake and amount of flakes in the paint.

Substitute a two-coat mica flake paint rather than a three-coat metallic flake paint. Mica flakes are far less sensitive to flake orientation dynamics, and nearly eliminate the risk of variation. However, mica-based coatings do not have quite as much brilliance and depth compared to metallics. For more information on mica and metallic paints or other finishes and services offered by Linetec, visit www.linetec.com, call 888/717-1472 or e-mail sales@linetec.com.

Common brand names of metallic and mica paints: