Original dial, ZentRa Manta. German made 17 J watch, steel case, ca. early 1970s. Final result below.
Dial after preparation. Dial removed. Paint was stripped with paint remover. I thought the hour indices were glued-on metal bars, and would fall off. Instead, they were part of the metal dial itself, molded with the dial as raised bars! These had to be taken down with sandpaper. After the photo above was taken, it was smoothed further with smaller grain paper.
Dial after painting. First picture is after a coat of primer, followed by white paint. Next, the blue ring was painted on. Ordinary enamel spraypaint was used. Masking of the dial for the blue and red paint used improvised household round items, admittedly imperfect (some bleeding resulted at the paint juctions.) Finally, a red circle in the center was painted. There is something called Frisket film, used by graphic artists, which provides a much better mask with a good seal, so there is no bleeding. I have not tried Frisket yet. Three finished pictures below.
I think the result is not bad for a first attempt. There is mild irregularity at the margins of the paint colors. If I try tomething like this again, I need to use better masking material, like this Frisket film I have heard about.
Strange footnote: in order to obtain spraypaint in Chicago you have to show your ID, and sign a some kind of waiver affirming that you don't plan on ubran vandalism. Some stores simply didn't stock spraypaint. These are the life and times of any modern day hobbyist. It is said that 90% of the items needed for a dirty bomb could be found at Jo-Ann Fabrics.