Before we can understand how to care for vehicles, we must understand the object before us. Central to our research is the 1952 Cunningham C-4RK, an aluminum-bodied race car with a nitrocellulose lacquer coating. The car was built by legendary racer and entrepreneur Briggs Cunningham with the goal of creating an American-built sports car capable of winning the 24-hour race at Le Mans.
The C-4RK performed beautifully at Le Mans, but ended up finishing 11th overall due to a crash during the 5th hour of the race. Regardless of its performance, the C-4RK proved that an American-built coupe could compete with its European counterparts. To this day, the car remains an icon in American racing history and its unique design influenced many cars that came after it.
Unfortunately, the C-4RK has begun to corrode due to a small layer of moisture trapped between the car’s aluminum body and its protective layer of nitrocellulose lacquer. While detailed studies of the corrosion of aluminum exist, there is a gap in the scientific literature concerning the preservation of a lacquered aluminum surface. In most cases, it is advisable to strip the lacquer from the aluminum surface in order to apply a newer, more durable protective coating. With an historic vehicle, however, there is clearly an interest in preserving its exterior finish.
To better understand the exact chemistry of the corrosion reaction occurring, it was necessary to find non-destructive ways to analyze the lacquer and the aluminum body of the race car. An x-ray fluorescence analyzer (XRF analyzer) proved capable of determining the chemical compositions of both the aluminum and the lacquer. With this information, it was discovered that the specific type of aluminum used to build the C-4RK corrodes at an exponentially decreasing rate, meaning that the car would take literally thousands of years to fully corrode. It also has become clear that devices like the XRF analyzer can be utilized to create large databases of readings that collectors can use to authenticate materials and predict how those materials would react to chemicals such as cleaning products.
Once it was discovered that the aluminum body of the race car was safe from severe damage, the focus of the research turned toward understanding the reactivity of the lacquer. As lacquer ages, it begins to “dry out”: this leads to microscopic cracks in the finish. These cracks are responsible for letting oxygen from the atmosphere penetrate through the protective coating and fuel the ongoing corrosion reaction. When researching what causes lacquer to dry out it, was discovered that many of the cleaning products that are advertised as safe to use on lacquer actually increase the rate at which lacquer degrades. By preferentially dissolving the plasticizers that give the lacquer its durability, these cleaning products cause the lacquer to become brittle and crack.
We are currently consulting with experts at the Smithsonian Air and Space Museum and investigating ways to seal the lacquer in order to stop the corrosion and preserve the race car.End