I have been asked to clean a new house for the first time, The window cleaning is straight forward, but she also asked me if I could clean the plaster off her window frames inside. They are stained wooden frames. The rough plaster comes off fine with a scraper, however it leaves a stain. If I rub it with a damp cloth or windolene type stuff, it disappears briefly but comes back when it dries. Any ideas? I am tempted to tell her to get the painter to sand the frames and re-stain them as I don't really want to be bothered with it, but if there's an easy solution I'll give it a go. I've attached a picture (I hope !).