I would just antique/stain over the gold paint with a waterbased acrylic. There is a color of Patio Paint (found at any craft store) called 'wrought iron black' which is a shade between a true black and a true brown. It would probably be perfect for your project.

All you need to do is brush on your paint(be generous), let it sit for about a minute, then with a soft rag rub the excess off. You might have to thin the paint a little to a stain consistency for a smoother application. Let it dry and if you need it darker repeat the process again. It is best to do several light coats instead of one heavy one because you will have more control over the end result. Repeat the process until you achieve the look you want.

*It's always best to do a small test area first before diving in to your project.

Thanks! I looked at Michaels and barely found any paints. I'll check at Hobby Lobby.

I lightly brushed a gold frame with a reddish paint, using a small foam brush, not worrying about coverage at all. After it was dry, which was pretty quick, I used a sponge to apply a rich dark paint, covering it mostly, with bare hints of the red coming thru. Worked great. I used little bottles of acrylic craft paint, purchased at michaels. I thought I might have to spray it with something but it's fine as is.

There are those rub-on metallic paste type paints that come in gold, silver, pewter, etc. If it fits the look you're going for, you might use your finger and rub some of that onto the painted frame to give it highlights. Then, buff it with a soft cloth (like and old t-shirt).