So grinding can be forgotten. I can't get into the rough structure with the abrasive.
Solvent doesn't really do anything. Little visible effect.
I tried a brush for the angle grinder. Doesn't work. It does get lighter, but I just pull the dark veil onto the surrounding area.
I tried the flame from the Bunsen burner. The effect is that some spots chip off very thinly and then look like new in that spot, but nothing happens to most of the surface. Too much gas consumption for too little solution.
My next approach would be an electric or pneumatic chisel. I ordered one for the Bosch hammer, but I suspect the cheap 20 euro chisels from Amazon won't withstand granite. (even though it says they are suitable for it)
I'll try it out. Maybe you can see an effect and then I'll buy a good chisel.
According to the information, even the chisels from brand manufacturers like Bosch are too soft for granite. According to the data sheet, they are only intended for concrete and tiles.
Are there possibly decent chisels from stonemason supplies?
Maybe someone knows something.