Here's an etch fill technique I've been trying out with mixed results; using wood filler to fill in the heavy etch on woods and plastics.
I've used it to fill in text on acrylic and it seemed to work pretty well; as long as the etch to be filled is not too large. On bamboo as shown below it's ends up thin enough you can see the grain underneath but you have a completely smooth surface. From my testing this doesn't work great on the veneers as you have to sand down the face some and the veneers don't give you much depth to work with.
Step One: I started by cleaning the smoke residue that is on bamboo pieces after laser cutting. I've found that you sometimes get it mixed into the white if you leave it on. If you have backing paper, it's better to leave it on until the final step.
Step Two: Apply enough wood filler to over fill your etch.
Step Three: I then used some acrylic scrap to spread the filler over the entire etch and put it aside to dry completely. The more you can get off the sides the less cleanup you'll have later.
Step Four: Once the filler dried I started sanding down the surface, trying not to round over the edges to much and not sanding too deep into the wider letters like the 'P'.
Step Five: I finished up by applying some wax/mineral oil to the wood, helping clean away any dust left from the sanding process.
As you might notice my second try didn't come out as cleanly. (bottom one) Above the 'k' you can see a small amount of over sanding and in the 'P' you can make out some of the letter has a thin spot.
Notes: On a glossy surface like hardboard, it might be possible to just use a damp cloth etches before the filler dries completely to remove excess filler. For acrylic I leave the protective paper on both sides and take it off once the filler is dry.
The brand of wood filler I used is Elmer's wood filler, it comes in white as well as darker colors like 'walnut'.