I used a regular black craft paint. I didn’t water it down at all, but you could if you feel like it’s too thick. I loosely painted over the lighter color with the darker, being sure to get it in the crevices.
You will need to work a bit quickly before it dries, and if you’re doing a large piece, just do one section at a time.
In the end, these look like they came from an old house in the middle of a prairie somewhere. They look like they have a story to tell. And, in a way, I suppose they do.