I'm going to try a little kodak retouching fluid, applied with a cottons swab, to the base side where the dust voids are and then use a very sharp, No. 2 pencil to build some density.
It is difficult to retouch with a #2 pencil as it does not allow itself to become sharp enough using a mechanical sharpener. Individual drafting leads available at an art supply store are what is needed. The majority of my negatives are done with an HB lead. To properly sharpen it you make an envelope of folded 400 grit sand paper. Tape the 2 sides with masking tape to keep the ground graphite off of everything. Using a Lead holder an adjustable drafting pencil (also available from the art store ) extend the lead out about 21/2 to 3 inches, place the extended tip of lead into your sand paper envelope.
With a pumping and twisting motion shape the lead into a long tapered (2 inches or more) needle shape. The long tapered lead delivers a very fine point of lead to the negative. The correct retouching motion is much like a tiny figure eight. The long tapered lead not only applies the lead controled by your steady hand, but serves as a pressure gauge as to how much pressure your hand applies to the negative. If the tiny sharpened tip breaks off, you have applied too much pressure. Re sharpen and begin again.
Use a very small amount of the retouching fluid most everyone at first applies to much. You know when you have too much, as the strings of the cotten ball begin to
pull out and deposit them selves on your negative. The fluid from the bottle usually has been in there for awhile so the viscosity is way heavier than is needed and should for best results be thinned. Apply a tiny drop on the cotten ball and apply it in a smooth circular motion as thin as possible, the fluid creates the tooth necessary for the lead to grab the neg.
The weight of the lead holder and lead are about the correct amount of pressure need to retouch a neg.
Charlie............................