In my last update we explored the corrosion problem plaguing the 1952 Cunningham C-4RK and we left off with the exciting possibility that sealing the C-4RK from oxygen might halt the corrosion altogether. In this post we are going to take a closer look at the external finish of the vehicle, a lacquer, and why that solution may not be so simple.
The term ‘lacquer’ is fascinating for my research because it is not so much a substance as it is a window of time. It refers to a coating made up of a substance, usually a polymer, dissolved in a volatile liquid that dries upon application. This creates a durable layer, capable of insulating an object from outside forces.
Lacquer has been used for centuries and is still heavily relied upon due to its ease of use and ability to protect different types of surfaces. A helpful way to visualize lacquer is to consider it as a bowl of spaghetti. The spaghetti noodles represent the polymers (long carbon chains) within the lacquer. The polymers give the lacquer rigidity and have a hard, brittle consistency when dried. The spaghetti sauce represents additives known as plasticizers and fillers, which consist of ethers and other chemicals that allow the lacquer to bend and form to the surface to which it is applied. Plasticizers increase the lacquer’s durability, allowing it to bend without cracking. The exact ratio of polymer-to-plasticizer defines the physical characteristics of the lacquer -- the more plasticizers a lacquer has, the softer and more malleable the lacquer will be.
The most notable feature of lacquer is that it doesn’t cure -- it merely dries. Curing refers to an irreversible chemical reaction where the molecules in a coating crosslink to form a solid surface. However, in lacquer no reaction takes place. Instead, the solvent molecules slowly evaporate, leaving a hard shell of polymers and plasticizers behind. This hard shell can be re-solvated or “re-wetted” by solvents, resulting in lacquer’s ability to be easily repaired when chipped. One simply adds new lacquer to the damaged area and the solvents in the wet lacquer dissolve the area around the chip resulting in a perfectly integrated repair.
Since lacquer can be repaired so easily one might ask, “Why not repair the chips in the C-4RK with lacquer?” In the case of the C-4RK, the catch is that there is no known original solvated lacquer left, so repairing the lacquer would require incorporating new material into an old finish. Not only does this have ethical implications as to what preserving a car and originality mean, but from a chemical standpoint it is very difficult to match the exact composition of the original mixture. Even small variances in lacquer composition result in differences in color and hue. It is also nearly impossible to match the characteristics of the existing lacquer due to the UV damage that has occurred.
The passenger door of the C-4RK is a perfect example of the difficulties of matching lacquer. It is believed that the door was repainted after a crash that occurred under 5 years after the car was built. The team made an attempt to match the lacquer perfectly, but as the picture below shows, the team was unsuccessful in matching the finish.
While it may not be possible to repair the chips in the C-4RK, I’ve taken another look at the idea of sealing the lacquer to prevent corrosion and protecting the surface from further damage. Malcolm Collum, head conservator at the Smithsonian Air and Space Museum, provided us expert advice on how such a task could be done. In museums, conservators like Collum use specifically engineered polymers that are capable of sealing an artifact from corrosive forces. The most important function of these sealants is to protect the artifact without altering its appearance. To protect lacquered surfaces it is common to use a microcrystalline wax that is very difficult to apply but it has the benefit of being removable. In the case of the C-4RK, Collum suggests against applying microcrystalline wax due to the fact that applying the wax could result in further damage to the lacquer.
In my next update, I’ll discuss the effects of common cleaning products on aged lacquer surfaces.End