Shooting Color: A Three Step Process
The final spray session actually begins with a preliminary step-the sealer coat-which technically is an extra primer coat. The sealer coat helps fill and smooth minute sanding scratches, and it imparts a consistent bed for the basecoat, which helps color uniformity. Primer sealers are designed to go on smoothly and require no sanding prior to the topcoat application. In auto refinish terminology, the topcoat is applied "wet-on-wet" over the sealer, meaning the paint is applied just after the solvents are allowed to flash from the applied sealer coat, in a matter of minutes.
 The first stage isn't a finish...  The first stage isn't a finish stage at all, but rather the sealer coat, which provides an improved surface for the color coats to come. We like the base tint to resemble the final color. |  The basecoat is where the...  The basecoat is where the real color comes on, though the finish is dull. With every step of the final spray process, the idea is to apply the material as smoothly as possible. |  Once given sufficient time...  Once given sufficient time to flash and dry to the touch, the basecoat can be given a light dusting with a tack-rag to remove any dry overspray that settled on the surface. |
One thing we like to do at the sealer stage is mix a sealer that is reasonably close to the color of the topcoat, orange in the case of our Corvette. Sherwin-Williams' sealer system comes in a full range of colors, and we used the available red and yellow to mix an orange primer. The advantage is the tinted sealer will allow the base color coat to "color-up" or hide the primer much more easily and consistently than would be the case with a contrasting base. Fewer coats of base will reduce the tendency for undesirable texture to develop while the color is applied. Another plus with a tinted primer is that minor stone chips that may come from driving the car are much less conspicuous if there is orange under the paint instead of a contrasting color.
For the final finish, we are using a basecoat/clearcoat system on this car, which is the most popular system in auto refinishing these days. This includes the basecoat, which gives the finish all its color properties, but none of the shine and durability of the completed paintwork. Once the sealer has been allowed to flash, the basecoat is the next step, but only after a careful inspection of the sealer coat. There is no room for flaws at this stage of the game, and if the sealer coat is rough from improper solvent selection, air pressure, contamination, or poor application technique, there is no use in continuing with the basecoat. Small dust nibs or other flaws need to be corrected without compromise.
The basecoat applies like the lacquer paints of old, going on with some solvent gloss, and then dulling and drying quite rapidly as the solvents flash out. The goal is to apply just enough basecoat for uniform color coverage, and no more. Two complete coats are adequate in most cases. Properly applied, the base should be smooth and consistently level, with imperceptible surface texture. As with the sealer coat, if the base does not meet these standards, there is no use in continuing with the clear before correcting the situation. You won't meet the goal of show-quality paint if the base does not lie down perfectly.