To most people a flat coat of shiny paint defines the perfect finish to a job well done. It's really hard to beat: manufacturers invested heavily to create resins that flow out to create glassy, rock-hard coatings. A freshly cured coat of paint really is a thing of beauty.
To others, though, a freshly applied coat of paint, no matter how nice, is merely another step in the finishing process. No matter how flawless a finish appears, a good detailer can find flaws in it. They're minute flaws of course, and without the aid of a magnifying glass most aren't even visible; however, like barely distinguishable stars in a night sky they culminate into a visual feature of their own. Only nobody waxes poetic about the multitude of barely perceptible specs in a paintjob.
Perfection is impossible but you can get damned close to it by color sanding the finish. In a nutshell the process removes the outermost skin of a paintjob, the surface with the flaws in it. But by color sanding you can also get damned close to the primer if you don't know what you're doing. So we consulted a guru of sorts. We asked Jason Killmer to show us how.
He forgives you if you don't recognize his name. Killmer is but one of the army of craftsmen stuck in a no-man's land in the sense that his best work is literally invisible. His objective is to remove the defects that people don't expect to see. Here's the cruel irony: the painter usually gets the praise for his best work. Those in the industry know the value in what he does and as a result literally fly Killmer around the country to work his magic on show cars as they reach various stages and at the big events to give cars the final once-over. Fortunate for us, though, he co-owns Polished Image, a detail shop in nearby Tacoma. Even luckier, he hosts seminars on how to make a finish shine like no other. Best of all, he puts up with me.
To understand how color sanding works it pays to know what determines the quality of a finish. Light reflects much like a billiard ball off a table cushion: both leave the surface at the inverse angle by which they arrived. In real-world terms, push a ball into the cushion at a 90-degree angle and it'll bounce right back at you at 90 degrees. Reduce the angle to say 15 degrees and it'll leave the cushion at the inverse angle, in this case 165 degrees (consult a protractor if that doesn't make sense). If a billiard table or protractor isn't handy then shine a flashlight in a darkened bathroom's mirror and see where the beam goes. And if that doesn't work then focus the beam upward on your face and summon a ghost to explain it for you.
They appear completely different but a mirror and the felt on a billiard cushion are similar in another respect. "A surface may look perfectly smooth but if you were to magnify it you'd see a bunch of tiny peaks and valleys," Killmer observes. Though seemingly insignificant, the miniscule transition from each peak to its respective valley reflects light. The severity and complexity of the reflective angles determine the surface's reflective qualities. The deep and infinitely complex crags in the felt, for example, reflect light rays in so many random directions that the surface appears dull. A mirror has the same peaks and valleys but they could hardly be described as craggy. The relatively small and shallow surface angles reflect light rays in a consistent direction thereby making the surface appear shiny. That's what we're going for.
"Color sanding is just an extension of the block-sanding process," Killmer continues. Only instead of flattening waves it levels all of those tiny ridges that scatter light indiscriminately. In fact, the same techniques used in block sanding largely apply to color sanding.
Killmer chose a driver-quality '56 Cadillac to show that nearly any finish can benefit from color sanding. It's a perfect candidate for at least two reasons. For one, the poorly applied paint has the ideal combination of dry spots, extreme orange peel, and a haunted mansion's worth of cobweb-like scratches. For another, its prior owner elected for a clearcoated finish, an essential component in this specific case.
The clearcoat is essential in this case because the car has a metallic finish. The resins that float to the surface of a single-stage metallic finish as it cures protect the metallic elements from oxygen. Color sanding, however, eliminates that thin protective coating thereby exposing those metallic elements, at which point they oxidize rapidly. A conventional clearcoat, on the other hand, is far thicker than the film that protects the metallic elements from oxygen. Provided it was applied sufficiently thick, the clearcoat will successfully protect a metallic basecoat. And just to clarify, a non-metallic finish needn't a clearcoat to benefit from color sanding. It has no metallic elements that would oxidize if exposed to the elements.
Which brings up something to consider. "If you're painting a car then spray a few more coats on there," Killmer suggests. By the time you finish color sanding and polishing a car, he explains, a really thick paintjob ends up about as thick as a normal paintjob that hasn't been color sanded. Bear in mind that this applies only to single-stage paints and the clearcoats in multi-stage finishes. The base and intermediate coats in a multi-stage finish needn't be any thicker. If you sand into them you've got bigger problems anyway.
You'll also need to develop a new way to gauge your progress. We're all used to examining things head-on but that perspective doesn't reliably reveal a surface's finish. For reasons defined in the reflectivity explanation you'll have to study the reflections that appear in a panel from an oblique angle. Killmer studies the light pattern created in the panel by a stand-mounted utility lamp. My camera preferred the dimmer and larger reflections created by the fluorescent lamps mounted to the walls. You'll likely find your own ideal light source.
But just as the case with paint, color sanding isn't the final step in a truly finished paintjob. Color sanding is merely the preparation for extensive polishing that follows, a task that warrants its own entry, an entry that will follow in the near future.