You can use white titanium gouache and a #000 Windsor Newton No. 7 fine sable brush. Use the back of a piece of resin coated paper as a mixing pallet and mix enough water so that you can get a smooth stroke on the neg. You might need a shot of good whiskey first.
Left out part 2: use the same brush to spot the gaping white area resulting from the first step. Similar process, mix your Spotone on the back of a piece of RC paper to match the tone of your paper, then re-recreate the grain pattern to match adjacent areas. I always had the best luck with a semi-dry brush - pull the brush along the pallet until most of the liquid is gone, turning the tip.