I'm not sure what finish you're after, but I met a custom blacksmith from the Czech Republic, who had an interesting technique. He would spray paint the iron w/ flat black paint, and while it was still tacky, sprinkle powdered graphite on it so it stuck to the paint. After it dried, he would rub it, concentrating on normal wear areas, so it would look like it had worn that way naturally. Wrought iron would tend to get shiny where it was touched, such as a handrail. I never actually saw him do it, but the results were great. I don't know off-hand where he got powdered graphite from.

Heat works also, but be careful! About fifteen years ago, the company I used to work for had a furniture store business with several branches among its holdings.

I wasn't directly involved in the furniture side of things, but they'd occasionally bring by pieces for repair since we had a fully-equipped shop to handle our equipment rental business.

One of the more common repairs, was to broken dining sets. The decorative wrought iron chair backs and legs took a beating, and needed welding. Even though the parts were fairly stout, they were often joined only by several small tack welds. Once the parts were cleaned up with a scotchbrite pad or sandpaper, they were either MIG welded, or gas welded if the parts were smaller. While the metal was still pretty hot after welding, the parts were spritzed with flat black spray paint. The heat crinkled the first coat of paint, and the texture/finish could be manipulated fairly easily with some practice.

The repairs were nearly invisible when done. If you can find something of similar size and density to the parts you're refinishing, you can practice a bit before committing to anything. Heat the pieces up with a propane torch or something similar, and fog on a coat of paint while the metal is still hot. If the metal is too hot, the paint will bubble and crinkle too much.....just experiment a little.

No- powder coat is a process where paint powder is electrostatically deposited, then baked on in an oven to a tough, but boring finish. This blacksmith's technique was decidedly low-tech. Graphite powder is used as a dry lubricant, among other things. He would just use spray cans of paint, then dust the graphite on by hand, and hand rub the normal wear areas. I've never tried it myself, but now you have me inspired to experiment!

You can also try touch up blue for firearms.
Depending on the metal aloy and surface prep the color can range from a deep black to the classic 'blue' color of a gun.
With the metal stripped of all oils and wearing gloves to avoid fingerprints you can heat with a hot air gun and swab on the blue.

Sounds like I need to do some experimenting myself...