Can I repaint a mantel with a nitrocellulose base?

As for painting over mantels, the paint is a nitrocellulose base, so any lacquer based material would work. However, do not prime it but instead scuff sand and finish. A poly finish over scuffed nitrocellulose base can usually give good results. Additionally, an oil based finish would definitely work. The key is to make sure the surface is prepped and ready to receive whatever finish is selected. Scuff sanding with a fine grit paper to get the surface prepped. A primer like Kilz will work and comes in a variety of paint compatible versions. A local paint shop confirmed that a good “gripper” primer that is water-based will work fine. The paint shop suggested a product called Adhero or Zinsser 123. Call your local paint professional and they will be able to recommend a primer that is water based that would go over the lacquer nitrocellulose based finish that is presently on the mantel.