This picture turned out a bit blurry, but you get the idea. I had these brass jewelry tags made for my necklaces and they came to me really shiny. I put a little vinegar in a small jar, attached a square of mesh over the top with a rubber band, put the tags on top of the mesh and closed the lid. I let the jar sit for 1/2 hour and they are perfectly tarnished. You can adjust the time accordingly for your own project, but just know that the tarnish will be uneven with this vinegar method. That's what I was going for, but if you want an even tarnish you will need to look into chemical usage.