I am working on an E. Howard N size gilt movement that was covered with what might be dried grease or oil. I have run the movement through an ultrasonic cleaner and soaked the affected parts in Naptha when they were still dirty, but to no avail. Because it is a gilt movement, I cannot use a hard abrasive. I am hoping that someone in this group has had the same experience and may have some suggestions on what I can do.

main plate

Tat is a toughie. I had a French clock come in for repair that had gilt plates with a similar problem. I was never able to find anything that would clean it. A little judicious scraping in a hidden spot, and a look-see under a 40x stereo microscope seemed to indicate that the gilt finish was gone under those spots, but I was never sure. I documented the problem with photographs and told the client. I returned the clock repaired and mechanically good, but was unable to do anything about the discoloration.