I googled how to clean bronze and there are two ways; lemon juice/baking soda or vinegar/salt/flour.
I didn't have any lemon juice so I went with the vinegar method. Basically, you mix equal parts of flour and salt then pour in just enough vinegar to make your flour and sugar a paste. Then rub it on your bronze piece.
I was in the process of putting "the stuff" onto the vase to clean it when I suddenly remembered I needed a picture!
My Honeypie to the rescue! He snapped me a photo:
[caption id="attachment_594" align="aligncenter" width="300" caption="Before"][/caption]
The site said to leave the paste on for 30 minutes, but for me, it didn't take that long. I was still rubbing the paste on when I started to see a noticeable difference. Being the impatient person I am I washed it all off before the thirty minute mark Probably at 15 minutes.
[caption id="attachment_593" align="aligncenter" width="200" caption="After"][/caption]
Viola! I wish I had a picture of My Honeypie's face when I showed him the after. I am super impressed with the vinegar/salt/flour method. You don't even have to wear gloves!