In this initial photo you can see just how rusted the bolt is.
Step 1: Remove That Rust!
Step 2: More Prep
The tops of the bolts were rough, so I put them into an electric drill and spun them on a sheet of sandpaper. First a rough grit, and moving up in finer grits until it was smooth.
Step 3: Electroplating!
It's pretty simple. I use a 5VDC adapter with the ends cut off. The solution is vinegar. The metal is a sheet of zinc. I got this piece from the same sheet metal fabricator I got the sacrificial piece from step 1. They used to use zinc sheets on slate roofs, so this could be a possible source. I was asked if a galvanized piece of metal would work, but I do not believe there isn't enough zinc present.
I let the piece of zinc sit in the vinegar for about an hour to make sure the solution was saturated with zinc. Then connected the positive terminal of the adapter to the zinc, and an alligator clip clips to the piece to be plated.
Once submerged, bubbles will form by the thousands - that's the water in the vinegar being broken down into hydrogen and oxygen. You can see the piece being plated in zinc very quickly! It should take you mere moments to cover. I plate once, wipe down with a rag and plate again.
You could then take a metal polish (like Brasso) and shine the bolt up to a mirror finish, but I was looking for an original finish, so...
Step 4: Blacken Those Bolts!
There are two methods of bluing...cold and hot. Cold involves a solution that gets wiped onto the piece. It contains selenium dioxide. Hot bluing involves dangerous temperatures and chemicals, neither of which I wanted to get into in my home.