Bronze is a copper alloy; therefore, when exposed to the elements it will naturally oxidise and form a green surface. While aged bronze is a style in itself, you may prefer to retain the pristine, shiny appearance your plaque originally had when you bought it.
This simple cleaning process will restore even the most weathered bronze plaques.
Remove the plaque from its mount (if it has one). Use a cotton cloth to wipe off any loose dirt or debris. Wipe between the engravings and crevices with a cotton swab to remove gunk from those hard-to-reach areas – alternatively, you could use a folded piece of sandpaper. Avoid touching the bronze directly with your hands after you've wiped it clean as the oils could cause further oxidation.
Mix together one part flour and one part salt – a few tablespoons should suffice. Add white distilled vinegar one drop at a time, while mixing the solution together. When it forms a composition with a similar consistency to toothpaste, it is ready to apply. If you don't have the ingredients to make your own cleaning solution, use a small amount of regular dish soap instead.
Use a clean cotton cloth to apply a thin layer of paste to the surface of the bronze. Rub in a circular motion with the cloth until the shine starts to return – you may blacken several cloths before you finally reach the surface! Again, use a cotton swab to get between the engravings and crevices. Leave the paste to dry, and then wipe it off with fresh cloths and cotton swabs – you may need to repeat this step several times.
Apply a thin layer of paste wax or leather dye to the bronze, leave it to dry, and then buff with a clean cloth – you may also need to repeat this step several times. For the best result, use a wax that has UV inhibitors as this will provide an added layer of protection.
When you're satisfied with the results, mount the bronze plaque back onto its base. Remember to wear gloves to avoid smudging it with finger prints!
Check the plaque frequently. When the wax starts to wear off, repeat this entire process. If you live in a humid area, you may have to apply the wax several times per year. Otherwise, once should be fine.