I am researching medieval graffiti and I need to enhance some photo that show some graffiti, however I don't seem to be able to really bring out the scratches. I have tried brightness/contrast, black&white, and various sharpens but nothing seems to help. The scratches are whiter than the stone, but the stone can be various shades of cream/grey/black. Can anyone give me some tips for this? This is an example of one of the worse ones...
The question is - are they your own photos? In that case, this is done with lighting. Go back and do it over.
If you have to work with other people's (poor) photos, there simply is no magic trick to this. You need to think differently. Start by setting the black and white endpoints to bring it up to full dynamic range. Even out the lighting with soft-masked adjustment layers.
That's just to get a workable baseline image. Next, identify the features in question. If you can't see it, it's not there, and no tricks can bring out something that isn't there to begin with.
If this is getting you anywhere, make selections. That's something Photoshop can work with.