The most common is fine pointed pencils. Negative retouchers generally had a selection from about 4b to 4h depending on how much was needed or how fine it had to be. The thick emulsion films of the past had a lot of 'tooth' on the emulsion to grab pencil, but the modern thin emulsion films have very little. The back side can also be retouched and the film thickness will provide some separation from the image to help blur the pencil work. It is a little harder to do because of the shiny surface. Use a cotton ball to apply a thin even coat of retouching fluid on the side you intend to do pencil retouching. It will help provide something to grab the pencil.
You need a light box of some sort to backlight the negative and a good magnifier to look through - a 4 inch diameter glass is better on the eyes than a loupe.
Do as much of your retouching on the base side rather than the emulsion especially if you are contact printing. Lopaka touches on the reasons why. Retouching on the emulsion side for contact prints places the pencil work exactly on the same plane as the grain in the emulsion thus it prints and shows the same degree of sharpness as each individual grain. If possible you do not want your pencil retouching to show in your final print.
Photrio.com contains affiliate links to products. We may receive a commission for purchases made through these links. To read our full affiliate disclosure statement please click Here.