I'd just sanded down the lacquer from my guitar, which worked pretty well. After a control of the surface I saw some white rough spots as you can see in the following pictures:
As far as I know it's ash wood. The spots only appeared after longer sanding these areas.
Now I have two questions:
1. What have I done wrong?
2. How can I remove these spots?
I looked at this question but it didn't really help me... Thanks for you help!