That is really neat, Roger! Beautiful subject… beautiful result! Fantastic!
I’ve been playing with my laser a bit more as well… trying to branch out into different materials and processes. I’ve played around with jumbo craft sticks before… but decided to see what engravings on painted and “white-washed” wood (birch?) might look like. So, I did a comparison between “white-washed” (left), painted (center), and bare wood (right). Same gcode, same 2.5 watt laser…
The “white-washed” is wood wetted with paint thinner, sprayed with flat-white paint, allowed to sit for a couple of minutes, and then wiped of most paint, and allowed to dry… ala @Bulldog 
Painted is just simple light coat of flat-white paint (same as I used with the ceramic tile), allowed to dry. And, of course, bare is totally untreated, just as it comes out of the package.
The paint definitely seems to give a “grainy” look to the image.
I have light air-assist running and you can see a bit of soot above the engraving on the painted piece (center)… maybe I need to roll it with a lint roller…
That definitely helps with the contrast and “grainy-ness”… now you can even see the “whites of their eyes”.
– David