Digital BW, The Print

Try spotting the spot with your choice of ink like one would with  
traditional photo prints. Or try Faber-Castell 6 set Pitt artist pen  
shades of grey (brush tips). These are India ink (pig), waterproof,  
smudge-proof and lightfast and acid-free, part #167104, about $12./17.  
They have worked for me.

Regards,
Marvin