You see them all the time, you know, the shimmery coatings on surfaces and products. Those metallic paints can be useful for coating anything from furniture, to mountain bikes, to automobiles. These paints tend to add a luxe shimmer to a surface that is appealing to the eye.
Metallics are an attractive coating, but they present challenges for touch-ups as anyone manufacturing products with a metallic finish will attest. Why is it so challenging to create a touch-up solution for a metallic coating?
First, let’s define metallic coatings. A metallic finish is anything that looks like metal or has a mirror-like reflective effect, sparkle, glitter, pearlescent, silver, bronze, gold, or chrome finish. There is a huge range, however, they all exhibit some sort of appearance change at different viewing angles. It is not always easy to tell if a finish is metallic or pearlescent as some finishes are quite subtle and it requires a trained eye or a special microscope to know for certain.
How are Metallics Made?
Metallic coatings are made with a variety of pigments that include aluminum and bronze pastes, aluminum and bronze powders and a range of mica and synthetic particles. All of these pigments come in different colors, flake shapes, and sizes that help contribute to the effect. There are many hundreds if not thousands of different metallic and pearlescent pigments available on the market.
These metallic and/or pearlescent pigments can be combined with opaque or semi-transparent pigments in the paint base to form the coating. There is a wide range of OEM (original equipment manufacturing) coating types and many of the metallic coatings are powder coatings, which means they are applied as a dry powder that electrostatically clings to the surface while it is melted into a solid coating through a baking process.
Why Metallics are Hard to Match
Consider metallic coatings as hundreds of thousands of tiny, reflective metal plates. How these plates are aligned within the coating film will affect how the coating looks and behaves (i.e. a mirror reflecting light toward you is light, and away from you is dark.). The term for this change in appearance is “the flip flop”, a simplistic way to describe the light/dark shift you see as you tilt the metallic coating. The behavior of this is greatly affected by the coating type and application method.
When someone needs to match a metallic it is usually because they need a touch-up application, or they need a seamless transition between a powder-coated part and a material that cannot be powder coated. It would be nice if you could just dab a little extra powder coating on the spot needing repair, but this is not possible with powder coating. (note: there are some methods to combine solvent with powder coating to create a touch-up but generally this technique doesn’t work very well). Powder coatings require an oven, and if it needs a repair, the part may need to be completely stripped and recoated – a very expensive and time-consuming process, not to mention the transportation costs to get the part back to the plant and then back to the customer. Therefore a touch-up solution that doesn’t require the part to be completely stripped doesn’t need to be baked, and/or can be applied in the field is ideal. This is the least expensive and easiest option.
Liquid paint offers the best option or touch-up paint. However, liquid paint is an entirely different chemistry and application than the original powder coat. The electrostatic application process affects the alignment of the particles and creates a particular flip-flop behavior. Even if the liquid paint were using the exact same ingredients (which it can’t), the absence of the electrostatic application would give it a different look. Typically, the liquid paint match will have an opposite flip-flop behavior than the powder coat. When you flip it in one direction the original powder coat will flip bright and the liquid will flop dark, and it reverses in the opposite direction. This means that for any viewing angle, the liquid and powder won’t match. We always match to a fixed 45-degree viewing angle.
Moreover, spectrophotometers and matching software cannot be used to formulate a metallic match (we wish they could!). Even the most expensive multi-angle spectrophotometers and expensive software can only be used to QC a match, not help create it.
Our process always begins with evaluating the part for color, particle size, and flash (aka how reflective) to select our starting pigments and then the sheen to select the starting base. From there, we intermix bronze, aluminum, mica pigments, colorants, and dyes to achieve the best possible mix. This is a scientific process for us, and involves not only a lot of experience but also a lot of experimenting! For each step, we keep detailed notes so that if we need to start over, we can improve on the last, best formula.
We have invested in an extensive pigment library (well over 60 different metallic and pearlescent pigments) combined with our even larger library of non-metallic pigments to give us a big range of materials to choose from. We are continually learning and adding new materials, processes, and techniques to achieve the best results.
Often, it’s just not possible to create an exact match with metallic coatings but we always do the best we can. The process takes time and we often go through several batches and iterations during the process. We often only know we’ve achieved “best” when everything we try makes the match worse. We’ve matched A LOT of metallic coatings so we know what we are doing.
Have a metallic you’d like to match? Learn more about our color-matching services.
