By far, the majority of classic...
By far, the majority of classic Corvettes came through with the acrylic lacquer paint used by GM from the late-'50s until the early-'80s. Though still available for those looking to do a true OEM resto, these paints have been replaced in the commercial refinishing industry in favor of much more durable catalyzed acrylic enamels and urethanes.
The drawback to the factory acrylic lacquer was definitely long-term durability, especially in comparison to today's materials. The paint was susceptible to chemical and environmental damage, fade, and loss of gloss over time. Worst of all, the paint became brittle with age and would crack and check, literally self-destructing. Although acrylic lacquers are still available, these paints are all but obsolete in the world of commercial automotive refinishing. About the only application where these products would be considered would be in contemplating an authentic OEM restoration.
Eventually, by the '80s, General Motors phased out the lacquer paints in favor of an evolution of modern paint materials, beginning with acrylic enamels, and leading to the basecoat/clearcoat material formulations in use today.
The basis for the modern commercial finishing processes today are acrylic enamels, urethanes, and increasingly, water-borne or water-based products. As noted, acrylic enamels have been utilized by the OEM manufacturers for many decades, and these paints have long been the standard for the refinishing industry as well. The common air-dry enamels are at the bottom rung of the acrylic enamel ladder, typically the material of choice for a low-dollar, blow-over paint shop. Air dry enamels are very slow to cure, are only moderately tough in terms of chemical resistance, polish poorly, and are prone to fade.
Single-stage paint in a urethane...
Single-stage paint in a urethane or even a high-quality catalyzed acrylic enamel can be used for either a representation of the original paint, or cut and polished to a mirror-like finish in solid colors.
As early as the '70s, highly developed catalyzed acrylic enamel formulations began to come on the market, with cross-linked chemistry that offered exceptional gloss, durability, and an excellent ability to be polished. With these very desirable attributes, the catalyzed acrylic enamels became the mainstay of the commercial and custom painting industry. These paints are still readily available, and offer outstanding value and results. For a single-stage paint application (no clear coat) to mimic the OEM lacquer paint, these catalyzed acrylic enamels are a viable alternative.
The next level in the evolution of paints was the move from acrylic enamels to urethane paints. These formulations essentially took the best attributes of the catalyzed acrylic enamels and went one step further in durability. Most commercially available paint product lines, particularly the higher-end products, are all urethane formulations.
By far, the most popular approach...
By far, the most popular approach to modern painting is using a urethane base/clear system. The base color is simply the color and contains none of the gloss properties of the final finish. The base sprays on with the dull gloss and quick drying reminiscent of a lacquer.
Paint product formulations are continuing to evolve, with many of the changes having to do with reducing toxicity and meeting environmental concerns. With this there is a move towards reducing solvents, particularly those classified as Volatile Organic Chemicals. VOC levels are closely regulated in the commercial refinishing industry in some areas, prompting paint manufacturers to revise formulations to meet the ever-tightening requirements. An evolution resulting from these forces is the expanding use of water-borne or water-based paint products. These products are designed with formulations to allow them to be soluble in water rather than petroleum-based solvents. While early on, these formulations had significant problems, ongoing development has led to much-improved and sometimes superior products that fit under this category. Some localities have mandated these formulations to replace solvent based paints in commercial refinishing.
Single vs. Two-Stage
With the advent of modern paint systems, so came the prevalent use of clear coats as the final top coat of the paint system. In older refinishing systems, the paint was what you got-and that was it. The color coats of paint carried all of the color, sheen, and gloss of the finish, a system now referred to as a "single-stage" paint system. This is the type of paint finish that was original to all older production cars, including classic Corvettes.