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Designs That Sparkle: Metallic Painted, Factory Finishes

Metallic paint coatings can add a vibrancy and visual appeal to architectural projects because of the way visible light reflects off the metallic flakes. But the same qualities creating depth and brilliance also may cause variations in appearance within a project or even within a single part. The question for architects, owners, contractors and material suppliers is how to minimize the risk of metallic variation and achieve the desired design.

The reflective property of metallic flakes means the same metallic 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 of the metallic flakes in the paint will affect the brightness of the color. Sometimes, this is referred to as the "flop of the flake"-the undesirable but necessary reality of metallic paints.

 

Optical Dynamics

To understand the optical dynamics of metallic paints, it helps 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 lay perfectly random. This will achieve the greatest level of "sparkle" and depth.

 

Consider two extreme alternatives:

If all the flakes in the paint lie horizontally, the surface will seem very bright because maximum light reflects back to the observer. If metallic flake content is high, the surface will actually appear to be a solid-color paint rather than a "sparkling" metallic.

 

In the other extreme, if all the flakes lie vertically in the paint, very little light reflects back to the observer making the surface appear dark. Here again, less "sparkle" will be apparent.

 

A consistently random flake orientation provides the ideal medium. Achieving this is practical and realistic with coil-coated sheet stock. With a coil-coating process, virtually all application variables are constant: part geometry (continuous flat sheet), spray distance, etc. This results in a consistent, random orientation of the metallic flakes, as well as uniform color and brightness.

A spray application cannot be as controlled as a coil-application process but typically must be used on any aluminum parts other than flat sheet in stock colors. The variability in the spray-application process reduces the ability to achieve perfectly random flake orientation. These process variables include different part geometries, electrostatic/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.

 

The Risks of Metallic Variation

Managing and minimizing the risk of metallic variation begins with recognizing projects with the greatest risk. Jobs that have the following design or location characteristics increase the risk of visible metallic variation:

  • Bright silver metallics-the paint applicator can advise if a particular metallic color presents a higher risk.
  • Wide, continuous painted surface area-a project with numerous, contiguous panels is more likely to show variation than a project with aluminum extrusions or one where panels are 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/bent panels are more likely to show variation than flat panels or sheets, and these issues may be accentuated with complex shapes and large parts.

 

Reducing the Risks

If the architectural project has the above characteristics, consider the following options to reduce that risk of color variation and achieve a more consistent appearance:

  • Paint all material at the same time. If not practical, at least paint all adjacent parts at the same time.
  • Minimize the number of paint applicators to better control color variations. Different paint applicators use different painting equipment, which create differences in color, especially with metallics.
  • Advise all building team members that some degree of variation is expected. Industry standard variation is typically 2 Delta Es, and samples can be provided to show what this looks 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 the paint applicator about alternative metallic colors. Some metallic colors are more prone to show variation because of differences in size of flake and amount of flakes in that paint.
  • Substitute two-coat mica flake paint rather than 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 always have as much brilliance and depth compared to metallics.

Above all, a collaborative relationship with the finisher will yield a quality metallic finish and the desired architectural statement.

 

Tammy Schroeder is the national marketing specialist for Linetec, Wausau, Wis. With a decade of experience in paint and anodize finishing, Schroeder develops and maintains Linetec's AIA/CES and other educational presentations.