From what I understand, scumbling was developed, in Victorian times or possibly before, as a way of transforming cheaper timbers I to more expensive ones, in the days when lower orders sought to emulate their “ superiors”. Thus, pine could be painted to look like oak, mahogany or other expensive hardwoods. Most of the cabins from working days were softwood, painted to look rather more expensive, often oak, sometimes with added mahogany details, though the boat yard men who did this were not highly skilled grainers who produced top class work. One, Kershaw if memory serves, exhibited grained panels at the Great Exhibition at Crystal Palace. He had to demonstrate his skills, the public not believing that it wasn’t the real thing. I’ve never aspired to such heights, although there are still those today with similar skills. Google wood grainers to see more.