I have installed a Trolla 109 in my house. It burns great. It's covered in surface rust, with no signs of paint or polish. I like the way it looks but I want to protect it for the future. I haven't been able to find any stove polishes that don't add a black color. What can I use to prevent continual rusting but not change the dark brown color? I tested some insulator wax (used for cars) on the back, and it's made a light brown spot, which I don't really like. Can I try some brown shoe polish? What else gets used on cast iron?