Very good work on removing the scratches from the blade so far Detlef. It should look great after you have finished both sides. The damage itself looks like a previous owner used a wire wheel on a grinder (most likely to remove rust) without realizing just how much damage it would do the metal. I am not sure what has caused more damage to blades, wire wheels or dremels.
If you would, please post more photos of this piece when it is finished for future reference. Congratulations on being able to add this most unusual piece to your ever growing collection.
Best,
Robert