Designs That Sparkle:
Metallic Painted, Factory Finishes
Tammy Schroeder,
Posted
04/01/2008
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.
www.linetec.com