You are reminding me of the many years I have on me. A long long time ago, when I was a wee lad in school, we did a project in shop using a similiar method. We made a lamp out of a large board about 6X8 or larger (can't remember for sure the size). We took a section about a foot or more long and threw it in a camp like fire and let it burn a few minutes before removing it and letting it cool. After cool, we took a wire brush and brushed out the grain and lose ash etc. Afterward we drilled the center and wired for a lamp and shade. I have no idea of the finish we used, but I would be willing to bet it was plain old varnish of some type being that long ago. I used that lamp for a very long time and was so proud of it. I wonder what ever happened to it over the years.
I may have to go out to the shop and make another someday now that you brought this reminder about.
Hope you and everyone here are having a great hoiliday