What a fantastic idea to shoot rust ; )
I like this a lot, very simple and well textured. The curly bits in the top corner look really interesting, would like to see a shot of that area too. Great shot, well done.
Awesome texture! This would have been even better if the bottom left and top right corner had been full in focus as well. Good idea though and of course it meets the challenge.
It's "oxidation".. I understand your plan to show rust as an effect of weather, but I don't think it's effective because the crop is too tight. I can't see that it's oxidation from this photo. Kinda looks like tree bark.