I used this deglosser (liquid sandpaper) to paint the spindles. Then I painted the spindles with a good quality trim paint. Painted over a year ago and I still smile when I see them. Good luck!
We did the same thing like Baxter with some spindles many years ago. The only thing that I might do is to use a separate coat of primer if they are in a place where people will put their hands on the constantly. Wishing you the best.
Just lightly sand gloss off and wash with TSP. Prime and paint with oil based primer. Our so far look new 20 years later. The secret is in the oil.
When I painted mine, it was the DIY method of sanding, priming and painting.