Q. My company manufactures a line of musical instruments, and I am the engineer in charge of finishing at our plant. One of our new lines of instruments has a polished brass dial face and we want a mirror-like finish on the face. We are trying to use a clear nitrocellulose lacquer to finish these faces. We are applying the lacquer with a manual air spray gun in our water wash spray booth. No matter how carefully we apply it, we have been getting bubbles and surface irregularities in the coating. What is the best way to coat these brass metal dial faces to get a mirror-like finish? M.J.
A. There are many possible causes of bubbles and surface defects in nitrocellulose lacquer finishes, including moisture in the atomizing air, excessive moisture from a water wash spray booth, gel particles in the lacquer, dry spray, and excessive film thickness. Other causes of bubbles are surface contamination due to improper cleaning, and airborne contamination drawn into the spray booth. I suggest you investigate each of these possibilities.
Although air spraying polished brass surfaces such as dial faces using nitrocellulose lacquer is a time-proven method, you may want to consider the use of other clear coatings. These would include materials such as acrylics, acrylic/urethanes epoxies, urethanes, vinyls, etc.