Tiger striping on balsa during engraving

Q: what causes these areas of no darkening on balsa wood? Glue?

Could there be some sort of residue on the wood from processing? Perhaps try sanding the wood before burning.

It’s hard to tell from the photo, but could that be the original grain of the wood itself? Balsa has fairly strong grain color.

The lightened areas don’t appear to have a grain type look … ?