After polishing your bangles, I rubbed a thin layer of wax on them. This is not a sealer, but should keep the bangles shiny for some time. You can keep them looking bright longer by keeping them in an air tight bag (such as a Zip Loc bag) when you are not wearing them. Adding an anti-tarnish strip, or one of those “oxygen eating” packets that come in many things you purchase, will help.
Over time however, the wax will wear off and even in the best of conditions, copper and bronze will darken. Many people like this patina; you can use a jewelry polishing cloth to gently shine them without removing the patina. Be sure to wash the bangles with gentle dish soap and water after using the polishing cloth.
If you would like to have your bangles look closer to new copper or bronze, you can try rubbing a little bit of ketchup into the metal – this works especially well with copper. Wash and use a polishing cloth to shine it up. Another option is to make a paste with lemon juice and baking soda and rub that into the metal (this may work better than ketchup on bronze). Again, finish by polishing with a polishing cloth and washing.
You can rub a thin coat of high quality paste wax after cleaning to protect it. I use Renaissance wax which can be purchased on Amazon, but any good quality paste wax should work.
I hope you enjoy your bangles for many years!