Hope someone can help. We have white walls in our kitchen, but they are quite grey in the corners due to soot from the wood burner. I am going to repaint, but feel I should remove the soot first. I've googled Soot Remover, and Amazon sell a sponge which is supposed to do the job. Has anyone used one and do they work (there were only 2 reviews), or should I just wash down with sugar soap? Thanks guys.