How do you know this? For example, there is a wikipedia page section entitled "Origin of use in the English language"...
https://en.wikipedia.org/wiki/Knocking_on_wood#Origin_of_use...
but the contents of that section make it extremely clear that no relevant facts are known to wikipedia.
But is is important to mention that a ctrl-f on that page for "unpainted" is proof that you didn't spend much time looking.