Dear Jerry, As a test, try one drop of laundry bleach placed in such a way as to overlap the paint and the surrounding (I assume unfinished since it's the back) oak. If the paint is oil, the bleach will not remove it. The bleach will clean the wood and the paint, as well, increasing the contrast between the two. If this works, do the entire area and then seal it with Wood Elixir which will bring back the natural color of the wood and make permanent the definition. Dr Woodwell