I learned from one of the best. It's definitely an art within itself to emulate the grain structure with the proper density. A lot of factors have to be considered such as the brush, ink, dilution, paper base tint, etc. I found myself oddly enjoying spotting and thus, became very good at it and spent many hours doing it. It's one of the few things in photography I know I can do very well ...not trying to rub it in or anything.